1 29

September 2010
Page 1 of 40
ROOF DECK SECUREMENT AND ABOVE-DECK ROOF COMPONENTS
Note to Insureds of Factory Mutual Insurance Company: Contact the local
FM Global office before beginning any roofing work.
Table of Contents
Page
1.0 SCOPE ................................................................................................................................................... 3
1.1 Changes ............................................................................................................................................ 3
2.0 LOSS PREVENTION RECOMMENDATIONS ....................................................................................... 3
2.1 Introduction ...................................................................................................................................... 3
2.2 Construction and Location ............................................................................................................... 3
2.2.1 General .................................................................................................................................. 3
2.2.2 Vapor Retarders (Barriers)—Design and Installation Recommendations ............................. 8
2.2.3 Roof Insulation .................................................................................................................... 10
2.2.4 Insulation and Roof Cover Fasteners .................................................................................. 11
2.2.5 Recover and Reroof Construction—Design and Installation Recommendations ............... 16
2.2.6 Structural Concrete, FM Approved Fiber Reinforced Cement and Lightweight
Insulating Concrete (LWIC) Decks: Design and Installation Recommendations ................ 17
2.2.7 Single-Ply Membrane Covers and Multi-Ply covers with Mechanically Attached Base
Sheets ................................................................................................................................. 18
2.2.8 Asphalt and BUR Installation Recommendations ............................................................... 22
2.2.9 Roof Covers Adhered to Mechanically Attached Base Sheets—Fastener
Installation Recommendations ............................................................................................ 22
2.2.10 Liquid Applied Roof Covers—Installation Recommendations ........................................... 23
2.2.11 Mechanically Fastened Base Sheet Assemblies Over Wood Decks—Design and
Installation Recommendations ........................................................................................... 23
2.2.13 Roof Deck Span and Securement for Wind Loads ............................................................ 25
2.2.14 Lightweight Insulating Concrete Roof Decks .................................................................... 29
2.2.15 Cementitious Wood Fiber Roof Deck Recommendations ................................................. 30
2.2.16 Lumber and Plywood Deck ................................................................................................ 30
2.2.17 Structural Concrete Roof Deck Recommendations ........................................................... 31
2.2.18 Torch Application of Modified Bitumen Roof Covers ......................................................... 31
2.2.19 Field Wind Uplift Tests ....................................................................................................... 32
2.2.20 Cold-Process Adhesives .................................................................................................... 32
2.2.21 Fiberglass Reinforced Plastic (FRP) Roof Deck ................................................................ 32
3.0 SUPPORT FOR RECOMMENDATIONS ............................................................................................. 33
3.1 Supplemental Information .............................................................................................................. 33
3.1.1 Class 1 and 2 Roof Decks .................................................................................................. 33
3.1.2 Wind Uplift Resistance, Non-Ballasted Roof Covers .......................................................... 33
3.1.3 Wind Uplift Resistance, Ballasted Systems ........................................................................ 35
3.1.4 Compatibility With Substrate ............................................................................................... 35
3.1.5 External Combustibility ........................................................................................................ 35
3.1.6 Recover Construction .......................................................................................................... 35
3.1.7 Wind Uplift ........................................................................................................................... 36
3.1.8 Wind Damage ....................................................................................................................... 37
3.1.9 Inferior Construction ............................................................................................................ 37
3.1.10 Steel Deck ......................................................................................................................... 37
FM Global
Property Loss Prevention Data Sheets 1-29
©2009 Factory Mutual Insurance Company. All rights reserved. No part of this document may be reproduced,
stored in a retrieval system, or transmitted, in whole or in part, in any form or by any means, electronic, mechanical,
photocopying, recording, or otherwise, without written permission of Factory Mutual Insurance Company.

4.0 REFERENCES ..................................................................................................................................... 39
4.1 FM Global ...................................................................................................................................... 39
4.2 Others ............................................................................................................................................ 39
APPENDIX A GLOSSARY OF TERMS ..................................................................................................... 39
APPENDIX B DOCUMENT REVISION HISTORY ..................................................................................... 40
List of Figures
Fig. 1. Hailstorm hazard map for United States (areas between dashed lines subject to severe hailstorms
and need an SH hail rated roof). ........................................................................................................ 9
Fig. 2. Insulation and vapor barrier mechanically fastened to steel deck. .................................................. 10
Fig. 3. Fastener placement 2 × 4 ft (0.6 × 1.2 m) boards. .......................................................................... 13
Fig. 7. Alternate corner increase for mechanically attached single-ply membranes. ................................ 19
Fig. 8. Fastener layout for 36 in. (914 mm) wide base sheet. ................................................................... 24
Fig. 9a. Side lap fastening: interlocking seam. ............................................................................................ 28
Fig. 9b. Side lap fastening: overlap seam. .................................................................................................. 28
Fig. 10. Two deck fasteners per support, one into each bar joist top flange. ............................................. 29
Fig. 11. Torch application of upper ply to a mechanically fastened base sheet — Note adhesive pooling
at the leading edge of the roll. ......................................................................................................... 32
Fig. 12a/12b. 4 × 4 ft (1.2 × 1.2 m) insulation boards secured with nine fasteners per board. ................ 34
List of Tables
Table 1. Recommended Rating of Field, Perimeter, and Corner Areas (Zones 1, 2, and 3) for
Enclosed Buildings ............................................................................................................................ 5
Table 2. Weight Needed of No. 3 Round Stone Ballast, Parapet ≤ 36 in. (914 mm) ............................... 21
Table 3. Weight Needed of No. 3 Round Stone Ballast, Parapet > 36 in. (914 mm) ................................ 21
Table 4. Weight Needed of Paver Blocks—not T&G, Beveled or Strapped to Each Other,
Parapet ≤ 36 in. (914 mm) ............................................................................................................ 21
Table 5. Weight Needed of Paver Blocks—not T&G, Beveled or Strapped to Each Other,
Parapet > 36 in. (914 mm). ........................................................................................................... 22
Table 6. Weight Needed of Paver Blocks—T&G, Beveled or Strapped to Each Other,
Parapet ≤ 36 in. (914 mm) ............................................................................................................ 22
Table 7. Weight Needed of Paver Blocks—T&G Beveled or Strapped to Each Other,
Parapet > 36 in. (914 mm) ............................................................................................................ 22
Table 8. Base Sheet Fastener Coverage for Non-FM Approved Combinations, ft2
per Fastener .......... 23
Table 9. Standard 36 in. (0.9 m) Base Sheet Fastening (Non-FM Approved Components). (See Fig. 8.) . 24
Table 10. Minimum Metal Disk or Fastener Head Size (Base Sheet Fasteners) ....................................... 25
Table 11. Allowable2
Uniform Uplift Pressure .............................................................................................. 26
Table 12. Nail pullout strength per in. (25 mm) of penetration .................................................................... 31
1-29 Roof Deck Securement and Above-Deck Roof Components
Page 2 FM Global Property Loss Prevention Data Sheets
©2009 Factory Mutual Insurance Company. All rights reserved.

1.0 SCOPE
This data sheet provides recommendations for the proper securement of various roof decks to supporting
members, and for the proper design and installation of above-deck roof components. Items covered include
roof covers, insulation, vapor retarders, fasteners, and recover assemblies. This data sheet is intended to
be used in conjunction with Data Sheet 1-28, Wind Design.
Prefabricated panel roofs, lap seam, and standing seam roofs are covered in Data Sheet 1-31, Metal Roof
Systems. Other data sheets with information on roofing include:
Data Sheet 1-28, Wind Design
Data Sheet 1-30, Repair of Wind Damaged Roof Systems
Data Sheet 1-32, Existing PVC Roof Covers
Data Sheet 1-33, Safeguarding Torch-Applied Roof Installations
Data Sheet 1-49, Perimeter Flashing
Data Sheet 1-52, Field Uplift Tests
Data Sheet 1-54, Roof Loads For New Construction (which covers positive [snow, ponding] loads)
For roofs of buildings divided by maximum foreseeable loss (MFL) fire walls, refer to Data Sheet 1-22, Criteria
for Maximum Foreseeable Loss Fire Walls and Space Separation.
1.1 Changes
September 2010. Minor editorial changes were made for this revision.
2.0 LOSS PREVENTION RECOMMENDATIONS
2.1 Introduction
The recommendations provided in this document are not intended to supersede the requirements of any
FM Approval (see Appendix A for definition). FM Approval listings outline the field-of-roof securement
requirements. Some listings also may contain specific roof corner/perimeter fastening methods. This data
sheet outlines other roof perimeter/corner fastening methods. Use the recommendations to supplement the
listings in the Approval Guide, a publication of FM Approvals. Where appropriate, recommendations are
grouped in each section as ‘‘Design,’’ ‘‘Installation,’’ and ‘‘Maintenance.’’
Roof systems are FM Approved only for certain wind uplift ratings. All recommendations are for systems
used within their FM Approval limits. Generally, recommendations regarding internal fire ratings (Class 1 or
2) are not applicable to structural concrete and gypsum roof decks, as these decks are rated noncombustible
(internally) regardless of the above-deck components due to the substantial thermal barrier offered by the deck
itself. Form boards used with gypsum decks may themselves be combustible.
2.2 Construction and Location
2.2.1 General
These recommendations are applicable to all systems except as noted.
2.2.1.1 Design Recommendations
2.2.1.1.1 Except for ballasted systems that are not FM Approved, ensure all installations use components
and systems (roof deck, insulation, fasteners, roof cover, etc.) that are FM Approved for use together on the
particular deck. Use of individually FM Approved components, not FM Approved for use together, does not
Roof Deck Securement and Above-Deck Roof Components 1-29
FM Global Property Loss Prevention Data Sheets Page 3

constitute an FM Approved or recommended assembly. Use of FM Approved systems is universally
recommended and is implied for all applicable assemblies whether or not specifically stated in the
recommendation.
2.2.1.1.2 All FM Approved materials are required to have the FM Approval mark on the packaging or the
material itself. Materials without proper labeling are not FM Approved and cannot be accepted.
2.2.1.1.3 Ensure the roof deck design and installation are in accordance with the Approval Guide, RoofNav
and Data Sheets 1-28, Wind Design, 1-49, Perimeter Flashing (and 1-31, Metal Roof Systems, where
applicable).
2.2.1.1.4 Use FM Approved perimeter flashing systems, where available. Secure wood nailers in accordance
with Data Sheet 1-49, Perimeter Flashing, and follow other guidelines in that document where FM Approved
flashings are not available.
2.2.1.1.5 Ensure roof slope is a minimum of 1° (1⁄4 in./ft, 21 mm/m). This can be accomplished by varying
the column heights or using an FM Approved tapered insulation system. Refer to Data Sheet 1-54, Roof Loads
for New Construction.
2.2.1.2 Installation Recommendations
2.2.1.2.1 It is essential that thorough supervision by the building owner’s qualified representative is provided
during all roof construction to ensure quality of workmanship and adherence to FM Approval standards and
project specifications.
2.2.1.2.2 When installing ‘‘torch-applied’’ roof covers, follow the recommendations in Data Sheet 1-33,
Safeguarding Torch-Applied Roof Installation, and recommendation 2.2.18.
2.2.1.2.3 Do not store combustible roofing materials in buildings under construction unless an adequate
sprinkler system is in service. Use combustible adhesives and solvents with caution. Use FM Approved safety
cans where appropriate. Do not allow smoking on roofs at any time. Do not allow ignitable liquids or solvents
to enter confined spaces. Ensure the facility’s emergency response team oversees all roofing work.
2.2.1.2.4 Make a minimum of two 10 lb (4.5 kg) ABC fire extinguishers available on the roof during roof
construction and repairs.
2.2.1.2.5 Due to possible high concentrated loads from the rolls of membrane and gravel carts, caution is
needed when moving these materials across the roof. To prevent over-stressing the deck when the weight
of individual rolls of single-ply membrane exceeds 1100 lb (500 kg), use precautions such as shorter deck
spans or plywood sheets over steel deck to reduce point loads.
2.2.1.2.6 Fill the space between nailers in roof expansion joints with noncombustible, compressible insulation
such as glass, mineral, or ceramic fiber type.
2.2.1.2.7 Provide adequate separation and/or noncombustible insulation between hot exhaust stacks and
combustible roof deck and above deck roof components. See DS 1-13, Chimneys, for details.
2.2.1.2.8 Ensure roof insulation or cover boards are dry and surfaces are free of debris or dirt prior to adhering
roof covers to them. This will help ensure complete adhesion of the cover to its substrate.
2.2.1.3 Maintenance Recommendation
2.2.1.3.1 Inspect roof systems and flashing semi-annually and after storms. During inspection, note and repair
any holes or deterioration of the covering, opened seams, backed-out fasteners, loose anchorages, loose
flashing, membrane shrinkage, etc. Replace any wet insulation when making roof repairs. Inspect and clean
drains as needed. Maintain written records.
2.2.1.4 Wind Uplift Resistance: Design Recommendations
2.2.1.4.1 Determine the roof wind uplift design pressure and recommended FM Approvals wind uplift ratings
for roof assemblies (decks and above-deck components) per Data Sheet 1-28, Wind Design or RoofNav
Ratings Calculator. Do not use any system beyond its FM Approval rating, except where enhancements are
allowed by this document.

2.2.1.4.2 Ensure all new, re-roof, and recover construction uses an appropriate wind-uplift-rated FM Approved
roof system where available. Ensure the roof field fastening is per FM Approvals RoofNav listing.
Note: For ballasted systems, see sections 2.2.7.4 to 2.2.7.6.
2.2.1.4.3 Because there are higher uplift forces on the roof corners and perimeter, these areas need
additional securement over that, which is FM Approved for the field of the roof. Refer to Data Sheet
1-28 for corner/perimeter definitions and dimensions. Ensure any whole or partial insulation board or roof
cover/base sheet width (when the roll is parallel to the building edge) that falls within the calculated perimeter
or corner has the increased securement applied over the entire board or roof cover/base sheet width. There
are several acceptable methods for increasing the uplift resistance of the roof in the corners and perimeters.
Do one of the following:
• Where the FM Approvals RoofNav listing includes a roof perimeter and/or corner fastening method, it can
be used.
• Use a roof system with the appropriate FM Approval wind uplift rating in each area per Table 1.
• Use the appropriate prescriptive recommendation noted in section 2.2.1.5, within the limits of acceptability.
• An alternative is to use an adhered roof cover (adhered across the entire roof) that is adequately wind
rated for the field of the roof and, in the perimeter and corner areas, use a mechanically attached roof
cover (see Table 1 and 2.2.7.2) that is either:
a) FM Approved for wind pressures in the perimeter and corner areas, or
b) FM Approved for the field of roof pressure per Table 1 and enhanced in the perimeter and corner areas
per recommendation 2.2.7.2.1 by reducing the distance between rows of fasteners.
In either case a) or b) above, fasten a termination bar over the cover or base sheet (with suitable
weatherproofing provided) and into the deck every 6 in. (150 mm) on center. Use minimum no. 15 screws
at the junction of the fully adhered areas with the adhered and mechanically fastened areas.
Table 1. Recommended Rating of Field, Perimeter, and Corner Areas (Zones 1, 2, and 3) for Enclosed Buildings
Roof Field Area Design
Pressure, p, (psf)2
Minimum Wind Rating for FM Approved Deck/Above-Deck/Entire1
Assembly
Roof Field Area Enclosed
Bldg.
Roof Perimeter Area
Enclosed Bldg.
Roof Corner Area
Enclosed Bldg.
p ≤ 30 60 105 150
30 < p ≤ 37.5 75 120 180
37.5 < p ≤ 45 90 150 225
45 < p ≤ 52.5 105 180 270
52.5 < p ≤ 60 120 195 300
60 < p ≤ 67.5 135 225 330
67.5 < p ≤ 75 150 255 360
75 < p ≤ 82.5 165 270 405
82.5 < p ≤ 90 180 300 435
90 < p ≤ 97.5 195 315 480
97.5 < p ≤ 105 210 345 510
105 < p ≤ 112.5 225 360 540
112.5 < p ≤ 120 240 390 585
120 < p ≤ 127.5 255 420 615
127.5 < p ≤ 135 270 435 660
1
Base the minimum wind rating on the roof field area rating when perimeter/corner areas are enhanced per this data sheet and other pertinent
FM Global Data Sheets (1-29, 1-31, etc.). Base the minimum wind rating on the respective area rating when perimeter/corner area
enhancements are not done, or are not acceptable.
2
For roofs with higher field area design pressures, or to interpolate needed perimeter and corner ratings when the field requirements are
between levels, multiply the needed field area design pressure from Table 3, 4 or 5 (of D.S. 1-28) by a safety factor of 2.0 and the respective
pressure coefficient per Table 6 of D.S. 1-28, and round up to the next highest 15 psf rating interval.
3
Ratings above apply to enclosed buildings, with roof slopes ≤ 7° and roof heights ≤ 60 ft (18 m).

2.2.1.5 Prescriptive Enhancement Options: Perimeter and Corner
2.2.1.5.1
a) For all deck types, where roof covers are adhered to some combination of mechanically fastened
insulation, cover board, or thermal barriers, prescriptive enhancements may be used for securement of
the perimeter and corner areas, as long as one of the conditions below applies:
1. The building is in a non-hurricane prone region where the design wind speed does not exceed 90
mph and the roof height does not exceed 75 ft (23 m). Note the roof height is limited to 30 ft (9.1 m) if
the building is located in surface roughness exposure D (see DS 1-28) and the building is partially
enclosed.
Or,
2. The recommended field of roof rating needed per DS 1-28 does not exceed Class 1-75 (3.6 kPa).
Or,
3. The building is in a non-hurricane-prone region (see Appendix A) and the recommended field of
roof rating per DS 1-28 does not exceed Class 1-90 (4.3 kPa).
For any of the three conditions above, increase the number of fasteners per board over the FM
Approved field-of-roof spacing by the following:
• 50% minimum in the roof perimeter, but at least one fastener per 2 ft2
(1 per 0.19 m2
). It is not
necessary to install fasteners closer than one per 1 ft2
(1 per 0.09 m2
).
• One fastener per 1 ft2
(1 per 0.09 m2
) in corner areas.
• Round up to the next whole number of fasteners, if necessary
b) For all locations (including hurricane-prone regions), where a Class 1-90 wind rated system is needed
for the field-of-roof, use the following generic assemblies in the perimeter and corner areas to provide
acceptable wind resistance in those areas:
Option 1
Minimum 11⁄2 in. (38 mm) thick, FM Approved, Class 1 insulation laid loose directly on the deck.
Minimum 1⁄2 in. (12. 7 mm) thick, FM Approved, water resistant, primed (factory or field primed) gypsum
cover board over the insulation. Primer can be omitted if roof cover / coverboard combination meets a
Class 1-225 or greater without a primer.
Through-fasten both layers to the steel deck with FM Approved minimum No. 14 (1⁄4 in., 6.4 mm) screws
and flat-bottom metal stress plates. Use 24 fasteners per 4 by 8 ft (1.2 by 2.4 m) board in the perimeter,
and 32 fasteners per 4 by 8 ft (1.2 by 2.4 m) board in the corners.
Roof cover – a fully mopped, minimum 3-ply BUR; or a minimum 2-ply mod bit system with all plies fully
mopped and/or torch applied per FM Approval requirements.
Option 2
Minimum 2 in. (50 mm) thick, FM Approved, Class 1 insulation laid loose directly on the deck. Note: a
lesser insulation thickness may be used if included in any Class 1 fire-rated assembly with the other
components above it, but not less than 1-1⁄2 in. (38 mm) thick.
Minimum 7⁄16 in. (11.1 mm) thick, oriented strand board (OSB) cover board over the insulation. Ensure
the OSB is APA (American Plywood Association) rated for Exposure 1, with exterior type adhesive.
Through-fasten both layers to the steel deck with FM Approved minimum No. 14 (1⁄4 in., 6.4 mm) screws
and flat-bottom metal stress plates. Note: if screws have oversized heads and are specifically approved
for OSB or OSB composite boards, stress plates are not required. Use 24 fasteners per 4 by 8 ft (1.2
by 2.4 m) board in the perimeter, and 32 fasteners per 4 by 8 ft (1.2 by 2.4 m) board in the corners.
Roof cover – a minimum 3-ply BUR or minimum 2-ply mod bit system with all plies fully mopped, per
FM Approval requirements.

c) For areas where the criteria in the recommendations above are exceeded, ensure the roof system used
in the perimeter and corner areas is FM Approved for the specific wind rating recommended in the
perimeter and corner areas (see Table 1). Alternatively, install either a mechanically attached single-ply
membrane, or a multi-ply roof cover with a mechanically attached base sheet in accordance with 2.2.7.2.
Note: Insulation and thermal barriers under mechanically fastened roof covers in assemblies that DO NOT
incorporate air or vapor retarders do not have to increase the insulation fastening over the field of roof
spacing.
2.2.1.5.2 For components adhered with urethane-based adhesives, asphalt, or other adhesives in ribbons,
spots, etc., reduce the spacing between ribbons or spots over the FM Approved field-of-roof spacing as noted
below (round down to a dimension that is practical with respect to board sizes, etc.):
• In the roof perimeter, not more than 60% of the field-of-roof spacing between rows or area
• In the roof corners, not more than 40% of the field-of-roof spacing between rows or area
Note: If the FM Approval rating for wind meets the criteria in Table 1 for the perimeter or corner area, no
further reduction is needed in those areas.
Example: A particular roof cover as FM Approved is adhered with a urethane-based adhesive in ribbons at
1 ft (0.3 m) on center in the field of the roof. The perimeter would need a ribbon spacing of 6 in. (150 mm)
and the corners would need a ribbon spacing equal to 4 in. (100 mm) on-center. Note: these spacings were
rounded down slightly for practicality.
2.2.1.5.3 For mechanically attached single-ply membranes, and multi-ply covers with a mechanically attached
base sheet, refer to section 2.2.7.2.
2.2.1.5.4 For mechanically attached base sheets, refer to section 2.2.9 or 2.2.11 if the base sheet is fastened
directly to a wood deck.
2.2.1.5.5 For ballasted systems, refer to section 2.2.7.4.
2.2.1.5.6 For steel decks, increase the number of deck fasteners at each joist or purlin support over the
field-of-roof FM Approvals RoofNav listing in accordance with 2.2.13. Shorter spans that yield an equivalent
increase in deck securement strength are acceptable, but may not always be practical.
2.2.1.6 External Fire Resistance—Design Recommendations
2.2.1.6.1 Assemblies having an American Society for Testing and Materials (ASTM) E108 Class A rating are
preferred in all cases, and are specifically recommended as follows:
a) Where the exterior fire exposure to the roof is severe.
b) On the entire roof of buildings subdivided by MFL fire walls. Refer to Data Sheet 1-22, Criteria for
Maximum Foreseeable Loss Fire Walls and Space Separation, for details on additional surface protection
needed adjacent to the wall and roof protection for buildings where MFL space separation is a factor.
c) For occupancies particularly susceptible to smoke or water damage.
2.2.1.6.2 ASTM E108 Class C rated assemblies are not recommended on any roofs >10,000 ft2
(930 m2
).
2.2.1.6.3 The use of pea gravel surfacing installed in accordance with 2.2.1.7.1 is considered to provide a
Class A exterior fire exposure rating. While not normally recommended in hurricane-prone regions due to
its potential to become windborne debris, it may be accepted in hurricane-prone regions (such as where
required adjacent to fire subdivisions), provided that all gravel remaining at the end of the installation is fully
embedded into the bitumen and there is no loose gravel nested on top. The following method will provide
such compliance:
a) Aggregate is applied into a flood coat of hot bitumen, and allowed to cool and harden.
b) Loose aggregate is pushed away, a second flood coat is applied, and the loose gravel is applied back
into the second flood coat and allowed to cool and harden.
c) Any remaining loose gravel is removed from the site .

2.2.1.7 Hail Resistance: Design Recommendations
2.2.1.7.1 Use only FM Approved roof cover systems meeting the severe hail (SH) criteria in the hail storm
hazard area shown in Figure 1. Unless specifically FM Approved with other surface treatments, built-up roofs
(BUR) may be used in SH and MH areas, provided:
• they are covered with gravel at a minimum of 400 lb per square (19.5 kg/m2
) or slag at a minimum of 300 lb
per square (14.6 kg/m2
). (See Appendix A, Glossary, for definition of square.)
• aggregate is in accordance with ASTM D1863.
• aggregate is applied into a minimum 60 lb per square (2.9 kg/m2
) bitumen flood coat.
Note: Do not use pea gravel in regions prone to hurricanes, typhoons ancd tropical cyclones except where
installed in accordance with section 2.2.1.6.3. Otherwise, use FM Approved coatings in lieu of pea gravel.
2.2.1.7.2 For U.S. locations outside the hail area, MH or SH rated systems can be used.
2.2.1.7.3 At locations outside the U.S., MH rated systems can be used unless local weather records indicate
the need for greater hail resistance. Generally, consider SH rated systems for locations with an average of
three or more hail storms per year.
2.2.1.8 Internal Fire Resistance—Noncombustible, Class 1, and Class 2 Assemblies—Design and
Installation Recommendations
2.2.1.8.1 As all FM Approved roof systems are Class 1 or noncombustible, Class 1 or noncombustible
assemblies are recommended in all cases. When there is an existing Class 2 deck and an unsprinklered
concealed space below the deck, refer to Data Sheet 1-12, Ceilings and Concealed Spaces, for fire protection
guidance.
2.2.1.8.2 Class 2 steel roof decks can be converted to Class 1 by applying an FM Approved undercoating.
If this is done, adhere to the following recommendations:
• Ensure the underside of the deck is clean before coatings are applied.
• Ensure FM Approved coatings are applied by applicators licensed by the coating manufacturer.
• Do not use cellulose-based undercoatings in high humidity occupancies as the fire retardant chemicals
are water soluble and can leach out of the coating.
• Do not use steel deck undercoatings where combustible residue can accumulate on the surface.
2.2.2 Vapor Retarders (Barriers)—Design and Installation Recommendations
These recommendations outline vapor retarder applications that maintain Class 1 and appropriate wind uplift
ratings.
2.2.2.1 If a vapor retarder is used, ensure it is FM Approved and applied in a single layer placed directly
on the deck. Side and end laps are sealed using FM Approved adhesive. The remaining roof components
are then installed with fasteners driven through the retarder into the deck (Fig. 2). The components above the
FM Approved vapor retarder can be any combination of materials FM Approved for use together on
the particular deck. Some systems are FM Approved with the retarder installed above a base layer of
insulation; see section 2.2.2.3 below.
2.2.2.2 On panel-type decks (decks with seams such as steel, wood, pre-cast planks, etc.), if a vapor retarder
is installed below the insulation or coverboard of a mechanically secured single-ply membrane (per
recommendation 2.2.2.1 above), secure the insulation or coverboard with FM Approved insulation fasteners
and plates using one of the following options:
1. A rate of 1 per 2 ft2
(1 per 0.19 m2
) throughout the entire roof area, OR
2. A rate throughout the entire roof area that will obtain a minimum 1-90 uplift FM Approval with an
adhered single-ply roofing membrane as specified in a RoofNav listing. The insulation/coverboard type
used below the mechanically secured membrane must match that specified by the RoofNav listing
for the adhered membrane, and the thickness of the insulation/coverboard must be equal to or greater
than that specified by the RoofNav listing.
A vapor retarder is located on the “warm side” of the roof or sandwiched between insulation layers. The vapor
retarder is sealed to the exterior walls of the building, but not necessarily to the underside of the roof cover.

©2009FactoryMutualInsuranceCompany.Allrightsreserved
Fig. 1. Hailstorm hazard map for United States (areas subject to severe hailstorms and need an SH hail rated roof)
FMGlobalPropertyLossPreventionDataSheetsPage9
RoofDeckSecurementandAbove-DeckRoofComponents1-29
Chattanooga
Concord
Nashville
Bangor
Memphis
Ludington
Louisville
Kapuskasing
Sault St Marie
Providence
Buffalo
Montpelier
Knoxville
Huntsville
Ottawa
Toronto
Montreal
BostonMarquette
Hartford
Green Bay
Kahoka
Chicago
Indianapolis
Albany
Milwaukee
Moline
Springfield
Saint Louis
Fort Wayne
Detroit
London
Saranac
Lake
NEWFOUNDLAND
Buchans
St. Johns
Montgomery
Gander
Mobile
Columbia
Charleston
Savannah
Atlanta
Jacksonville
Tampa
Ashville
RaleighWytheville
Norfolk
Richmond
Charleston
Cincinnati
Columbus
Cleveland
Pittsburgh
Harrisburg
Philadelphia
Little Rock
Sidney
Jackson
Charlottetown
Miami
Chatham
Amherst
Quebec
Shreveport
Baltimore
New Orleans
Washington DC
Trenton
Birmingham
Halifax
Port Arthur
Churchill
Saskatoon
The Pas
Winnipeg
Sioux Lookout
Souix City
Des Moines
Minneapolis
Regina
Pierre
Duluth
Fargo
Bismarck
Aberdeen
Kansas
City
Sioux
Falls
North Platte
International
Falls
Prince
Albert
Medicine
Hat
Calgary
Edmonton
Cranbrook
Vancouver
Penticton
NelsonVictoria
Clayoquot
Kamloops
Prince
George
Prince
Rupert
Havre
San Diego
Fort Smith
Springfield
MEXICO
Joplin
CANADA
Houston
Fresno
Baker City
Denver
Williston
San Antonio
Pueblo
Dallas
Las Vegas
Boise
Oklahoma City
Portland
Cheyenne
Tucson
Los Angeles
Phoenix
Wichita
Santa Fe
Spokane
El Paso
Topeka
Amarillo
Seattle
Sacramento
Eureka
San Francisco
Red Bluff
Pocatello
Reno
Salt Lake City
Sheridan
Lander
Helena
Billings
Pacific
Ocean
Atlantic
Ocean
Gulf of Mexico
Gulf
of
California
H ecate
Strait
Ja mes
Bay
Gulf of
St. Lawrence
Gulf of
Maine
Lake
Huron
Lake
Michigan
Lake Superior
Hudson Bay
200 0 200 400 Kilometers600
0 200 400 Miles200
Exposure to
Damaging Hailstorms
Moderate
Severe
No Data
25°
55°
50°
45°
40°
35°
30°
75°80°85°90°95°100°105°110°115°120°

An air barrier is used with a mechanically fastened roof cover and is located directly above the roof deck.
The air barrier is sealed to the underside of the roof cover, but not necessarily to the exterior walls of the
building. In theory, an air barrier improves wind uplift resistance of the roof assembly by preventing air flow into
the space below the roof cover and transferring a portion of the uplift load to the insulation. It should be noted
that even for properly installed air barrier systems, roof penetrations made after the installation of an air
barrier system can hamper the wind performance of an air barrier system if the air barrier is not sealed to
the underside of the roof cover after the penetration cut is made. Consequently, there are special FM
Approval restrictions on air barrier systems.
2.2.2.3 Fastener penetration of the vapor retarder can be avoided by using an FM Approved fastened/adhered
assembly. Ensure all materials are FM Approved for use in combination. Ensure substitution of
materials is not made.
2.2.2.4 Do not mop asphalt/felt vapor retarders directly on to any deck (this would result in a Class 2 roof)
except structural concrete.
2.2.3 Roof Insulation
2.2.3.1.1 Ensure insulation boards are FM Approved for the specific application, including specific roof cover,
fasten/mop construction, multiple layers, etc. Using assemblies that are not FM Approved can result in a
Class 2 and/or inferior roof construction. However, combinations that may not be FM Approved but can be
accepted are noted in sections 2.2.3.1.2, 2.2.3.1.3, and 2.2.3.1.4.
2.2.3.1.2 It is acceptable to use multiple layers of FM Approved insulation, mechanically secured through
all layers, provided all of the following are true:
• All layers are the same insulation.
• The total insulation thickness is not greater than the maximum FM Approved thickness of the insulation.
• The mechanical fastening and wind uplift rating are per the FM Approval of the top layer.
• The roof cover/insulation/fastener combination is FM Approved.
2.2.3.1.3 Insulation board sizes listed in the Approval Guide are the minimum FM Approved sizes. Boards
up to 4 × 8 ft (1.2 × 2.4 m) can be used except as noted in section 2.2.3.1.4 (with a proportional increase
in fasteners, adhesive ribbons, etc. rounding up to the next whole number). Do not use boards smaller than
FM Approved except per section 2.2.3.2.2.
Fig. 2. Insulation and vapor barrier mechanically fastened to steel deck.

2.2.3.1.4 The maximum recommended insulation board size, if the board is adhered with asphalt or adhesive,
is 4 × 4 ft (1.2 × 1.2 m). Exception: Flexible boards such as maximum 1⁄2 in. (13 mm) thick wood fiber or
5⁄8 in. (16 mm) gypsum board may be adhered at board sizes up to 4 × 8 ft (1.2 × 2.4 m).
2.2.3.2.1 Stagger insulation board joints in one direction (the shorter sides staggered if boards are not square).
Support the two opposite sides of each board on steel deck flanges, as close as practical to the center of
the flange with a minimum bearing width of 1 in. (25 mm). Trim board edges if they veer off the flange center.
2.2.3.2.2 When insulation boards are cut, as is common at the roof edge to produce staggered joints, secure
each piece with the appropriate number of fasteners, adhesive ribbons, etc. for the full board times the
percentage area of the piece, rounding up to the next whole number.
2.2.3.2.3 Install only as much insulation or gypsum-based board as can be covered each working day. Seal
loose roof cover edges at the end of each day to minimize moisture damage. Do not allow water to run in
steel deck ribs under completed roof sections.
2.2.3.2.4 Ensure insulation is set on pallets or dunnage and protected from the weather and sunlight prior
to installation. Do not allow plastic to cover the insulation as it can allow condensation. A breathable material,
such as canvas, is recommended.
2.2.3.2.5 Ensure FM Approved job-mixed material (like LWIC) is installed by applicators licensed by the
manufacturer. Steel deck that meets the insulation manufacturer’s span and gauge requirements is necessary
to support the application equipment. Such systems are a possible option when penetration of the deck with
mechanical fasteners is not desired.
2.2.3.2.6 Provide preliminary securement of insulation boards when mechanically fastened roof covers are
used (single-plies or multi-plies with fastened base sheets). Install a minimum of two fasteners per 4 x 4 ft (1.2
x 1.2 m) board or four fasteners per 4 x 8 ft (1.2 x 2.4 m) board, unless the manufacturer requires a greater
number. Additional insulation fastening is not required in the perimeter and corner areas. Where a vapor
retarder is used below a mechanically fastened roof cover, see section 2.2.2.2.
2.2.4 Insulation and Roof Cover Fasteners
2.2.4.1.1 FM Approved insulation fasteners are the only FM Approved and recommended method of securing
insulation boards or other boardstock materials to steel deck. Some fasteners are FM Approved for other
deck materials.
2.2.4.1.2 When fastener pull-out tests are performed on new construction to evaluate the deck integrity
or evaluate decks that are not FM Approved, run a minimum of five tests and use the average value. See
section 2.2.5.2.6 for the number of tests for recover/reroof construction.
2.2.4.1.3 When pull-out tests are done, base the fastener density on the more conservative of either the
FM Approved spacing for the fastener plate/insulation/roof cover combination, or the spacing needed based
on the average pull-out performance.
Example: An existing deck is oriented strand board (OSB). The fastener/insulation/roof cover combination
is FM Approved for 4 fasteners per 4 × 4 ft (1.2 × 1.2 m) board for Class 1-90 on steel deck. The calculated
load per fastener would be 360 lb (1600 N) ([4 ft2
/fastener][90 psf] = 360 lb/fastener). If the proposed fastener
achieved a pull-out resistance of 360 lb (1600 N) or more in the deck, the FM Approved spacing would be
used. If the fastener achieved a resistance of less than 360 lb (1600 N), for example 300 lb (1335 N), calculate
the spacing as follows: (16 ft2
)(90 psf)/(300 lb) = 4.8 fasteners per board; use five fasteners per board in
the roof field. Additional fasteners would be needed in the corners and perimeter per section 2.2.1.4.3. The
percentage increase would be applied to five fasteners per board, not four.
2.2.4.2.1 Install fasteners only through dry substrates. Wet constructions can cause deterioration of fasteners,
including FM Approved corrosion-resistant fasteners. Exception: Fasteners FM Approved for use in new
lightweight insulating concrete decks are designed to be tolerant of the moisture present at the time of
installation.

2.2.4.2.2 Use only FM Approved fastener/plate combinations. Do not install stress distribution plates from
one manufacturer with another manufacturer’s fastener unless the combination is FM Approved.
2.2.4.2.3 Fasteners must be driven perpendicular to the deck to be effective. Particular caution is needed
with tapered insulations.
2.2.4.2.4 Use the manufacturer’s proprietary installation tool. A less desirable option is a properly adjusted
screw gun, having a depth-sensing clutch, to avoid over-driving or under-driving screw-type fasteners.
2.2.4.2.5 Recommended Fastener Embedment:
Sructural concrete: 1 to 11⁄2 in. (25-38 mm),
Wood decks: Minimum 1 in. (25 mm). Note: For 3⁄4 in. (19 mm) thick plywood deck, approximately 1⁄4 in.
(6 mm) of the screw will protrude through the deck underside.
Steel deck: For screw-type fasteners in new construction, use the shortest screw that is at least 3⁄4 in.
(19 mm) longer than the assembly being secured. Ensure fasteners engage the deck top flange. For recover
steel deck construction, the fastener must be long enough to be driven through the existing roof system and
into the deck at least 3⁄4 in. (19 mm). While top flange engagement is recommended in all cases, for recover
construction, it is acceptable for insulation fasteners to engage the bottom flange of the deck. Ensure
fasteners securing mechanically attached roof covers engage the top flange of the deck in all constructions.
For other deck types: Follow the FM Approval requirements and manufacturers’ specifications.
2.2.4.2.6 Ensure insulation fastener placement is per Figures 3, 4, 5, and 6. If a particular insulation has a
different required FM Approved fastener pattern, use that. Each fastener must engage the intended deck
flange. This results in a spacing tolerance of approximately ± 1.5 in. (± 38 mm) for wide-rib deck if the edge
of the board was at the centerline of the deck top flange. For smooth decks, such as plywood or concrete and
steel deck in the direction of deck ribs, a maximum tolerance of ± 1.5 in. (± 38 mm) is acceptable.

Fig. 3. Fastener placement 2 × 4 ft (0.6 × 1.2 m) boards.

For fastening densities not shown, the following guidelines apply:
• Ensure edge fasteners are 6 in. (152 mm) from the board edges, with tolerance as above.
• Ensure fasteners are evenly distributed over the board area.
• Ensure all fasteners engage the top flange of steel deck. (See note for recover construction, section
2.2.4.2.5 above.)
2.2.5 Recover and Reroof Construction—Design and Installation Recommendations
This section covers planned recover and reroof operations. For repairs after wind damage has occurred,
refer to Data Sheet 1-30, Repair of Wind Damaged Roof Systems.
2.2.5.1 Reroof Construction—Removal and Replacement of Above-Deck Components
2.2.5.1.1 Reroof construction is generally preferred to recover construction due to the potential for moisture
damage with recover construction from existing wet insulation inadvertently left in place.

2.2.5.1.2 When reroofing, inspect the existing deck securement and, if necessary, fasten the deck per Data
Sheet 1-28, Wind Design, prior to installation of the above-deck components.
2.2.5.1.3 When reroofing over a steel deck where the original assembly had been adhered with asphalt, do
one of the following:
• Use an insulation specifically FM Approved for reroofing; that allows up to 15 lb per square (72 kg/100 m2
)
of asphalt to remain on the deck.
• Remove all asphalt from the deck and install a system FM Approved for new construction.
2.2.5.2 Recover Construction—Existing Components Remain
All recover recommendations and FM Approvals are based on the assumption that there is only one existing
roof system. If more than one roof system is in place (building has already been recovered), use reroof
construction.
2.2.5.2.1 If recover construction is considered, perform the following actions:
• Remove all wet materials prior to application of the new roof system, with wet insulation being replaced
with dry material.
• Cut out blisters.
Roof cover blistering or rusting deck may be an indication that the existing insulation is wet. When this is
observed, take one of the following steps:
• Reroof, as opposed to recover. See section 2.2.5.1.
• Conduct an infrared or nuclear examination to detect any high-moisture content.
If moisture is detected with one of these nondestructive methods, confirm the results by cutting out 1 × 1 ft
(0.3 × 0.3 m) samples or roof cores as needed to determine the extent of wet insulation.
2.2.5.2.2 Recover—mechanically attached recover systems. If the existing construction is dry, an
FM Approved recover system can be applied over it. Ensure the entire assembly (insulation, fasteners,
and roof cover) is FM Approved in combination for recover construction on the particular deck.
2.2.5.2.3 Ensure the thickness of the recover system is within the FM Approval limits. Most systems are limited
to a maximum 1 in. (25 mm) thick roof insulation. A greater thickness may affect the Class 1 fire rating of
the completed system. Installation of an FM Approved Class 1 recover assembly over an existing Class 2 roof
system will not upgrade the assembly to Class 1. However, it would be possible to upgrade the external
fire resistance rating (E108) with the addition of an FM Approved roof cover system.
2.2.5.2.4 When brooming gravel from the roof, do not pile it in one area. This can overload structural members
causing collapse.
2.2.5.2.5 Do not use recover constructions using additional plies adhered directly to an existing BUR unless
the entire assembly is FM Approved. This would essentially result in a 6- or 7-ply BUR over the insulation
(3- or 4-ply existing BUR plus 3 plies added), most likely creating a Class 2 roof assembly.
2.2.5.2.6 When reroofing or recovering over gypsum, cementitious wood fiber, or lightweight insulating
concrete decks, verify fastener pull-out performance with field tests. Perform 5 pull-out tests per 50,000 ft2
(4650 m2
) using FM Approved fastening or a minimum of 5 tests. Run additional tests if inconsistent results
are obtained. On larger roofs, the number of tests above the minimum can be reduced if consistent results
are obtained. Fastener spacing is calculated per section 2.2.4.1.3. It is not necessary to run pull-out tests
of fasteners FM Approved for installation in steel deck, structural concrete, nominal 3⁄4 in. (19 mm) plywood,
or nominal 2 in. (51 mm) lumber decks, unless the condition of the deck is in question.
2.2.6 Structural Concrete, FM Approved Fiber Reinforced Cement and Lightweight Insulating
Concrete (LWIC) Decks: Design and Installation Recommendations
NOTE: also see section 2.2.14 for LWIC and 2.2.17 for Structural Concrete Decks
2.2.6.1 When an FM Approved asphaltic adhesive or asphalt is used to secure components to these decks,
prime the deck with an FM Approved primer at the FM Approved rate, or with an ASTM D-41 asphalt cut-back
primer at 0.75 to 1.25 gal per square (3.0 to 5.1 L/10 m2
).

2.2.7 Single-Ply Membrane Covers and Multi-Ply covers with Mechanically Attached Base Sheets
Loss experience has shown that even properly secured single-ply roof covers can be damaged by windborne
debris such as metal panels and broken glass. In areas prone to hurricanes, typhoons and tropical cyclones
(see DS 1-28), use more durable roof covers. This would include multi-ply roof covers or single-ply
membranes that are considerably thicker than the FM Approved minimum. Many single-ply membranes are
manufactured in thicknesses up to 0.080 to 0.090 in. vs. the minimum FM Approved thickness of 0.045 to
0.060 in.
2.2.7.1 General
2.2.7.1.1 Single-ply membranes can deteriorate when exposed to certain materials commonly discharged
onto the roof. Also separate these membranes from incompatible substrate materials. In particular, ensure
single-ply membranes do not come into contact with asphalt or coal tar-based materials. Ensure EPDM
membranes are not exposed to gasoline, oil, solvents, or animal fats. Ensure PVC membranes are not in
direct contact with EPS. Follow the manufacturer’s recommendations for protection or separation.
2.2.7.1.2 Some FM Approved single-ply membranes are formulated with fire retardants on the top side only.
Install these systems with that surface up. Membranes with this requirement are labeled on the underside
‘‘THIS SIDE DOWN/IN.’’
2.2.7.2 Mechanically Attached Single-ply Membranes and Multi-Ply Covers with Mechanically
Attached Base Sheets: Design Recommendations
2.2.7.2.1 In the roof corners and perimeter, ensure the distance between rows of roof cover fasteners or
batten bars are the following maximum percentages of the FM Approved spacing. Use the reduced spacing
in all FM Approval classifications:
Roof Perimeter: Distance between rows is ≤ 60% of the FM Approved roof field spacing, or one row of
intermediate fasteners is provided in between.
Roof Corners: Distance between rows is ≤ 40% of the FM Approved roof field spacing or two rows of
intermediate fasteners are provided in between. An alternative for Class 1-75 and below (on steel deck) is
to install perimeter fastener rows (60% of roof field as above) in both directions in the corners (any wind class
acceptable for other types of decks). Refer to Figure 7. When the cover overlaps in the corner areas, install
these fasteners from above the uppermost cover layer.
• For single-plies fastened along the side laps:
Increased fastening density for single-ply membranes is often obtained by using narrower sheets. For
single-ply membranes or base sheets, intermediate rows of fasteners may be installed through the sheet
with a cover strip or additional plies applied over the fasteners, in accordance with the manufacturer’s
instructions. Use one intermediate row in the perimeter and two intermediate rows in the corners. Fastening
increase is not always obtained by increasing the number of fasteners along each row, unless substantiated
by FM Approval test data or otherwise done to provide a more practical spacing and distribution of wind
loads. In some cases, such as over wood decks (see 2.2.11) or LWIC, or with mod bit base sheets in high
wind areas, enhanced securement for base sheets is provided by reducing the fastener spacing within and
between rows in order to provide a uniform distribution (see section 3.1.2.1 for examples). When steel deck
is used, the fastener spacing across the deck ribs must be in even multiples of the deck rib spacing (6 in. or
150 mm for 11⁄2 in. or 38 mm deep deck) to ensure the fastener engages the top deck flange. See Example 1.
• For point-attached membranes:
Increased fastening density is obtained by decreasing the spacing between fastener points in one or both
directions. Ensure total tributary area to each fastener is no more than 60% and 40% in the perimeter and
corners, respectively, of the FM Approved roof field spacing. See Example 2.
Example 1: A batten-attached system with FM Approved fastener spacing for Class 1-60 of rows 6 ft (1.8 m)
on center and screws 6 in. (152 mm) on center would use 3.6 ft (1.1 m) maximum on center row spacing,
with 6 in. (152 mm) on-center screw spacing in the perimeter and 2.4 ft (0.7 m) maximum on-center row
spacing with 6 in. (152 mm) on-center screw spacing in the corners. In this case, rows of roof cover fasteners
should extend across the deck ribs in all areas to properly distribute the load to points of deck securement.
Since the needed wind uplift rating is limited, an option would be to use row spacing of 3 ft (0.9 m) maximum
in both directions in the corners per Figure 7, and 2.2.7.3.2.

Fig. 7. Alternate corner increase for mechanically attached single-ply membranes.
Note: Fastener spacing along all rows is the same as field spacing.
Notes: 1. Fastener spacing along all rows is the same as field spacing.
2. See section 2.2.7.3.2. for restrictions on fastener rows parallel to steel deck ribs.
3. If two layers of membrane are installed in the corner areas, all fasteners must secure the top
layer.

Example 2: A point-attached system with FM Approved fastener spacing for Class 1-90 of 24 × 24 in.
(610 × 610 mm) could use a spacing of 14 × 24 in. (356 × 610 mm) in the perimeter. A 12 × 24 in.
(305 × 610 mm) spacing may be needed for steel deck applications depending on deck rib direction.
A spacing of 10 × 24 in. (256 × 610 mm) in the corners could be used. A 12 × 18 in. (305 × 457 mm) may
be needed for steel deck applications depending on deck rib direction.
2.2.7.3 Mechanically Attached Single-Ply Membranes and Multi-Ply Covers with Mechanically
Attached Base Plies—Installation Recommendations
2.2.7.3.1 Ensure all roof cover fasteners engage the top flanges of steel deck.
2.2.7.3.2 Install batten bars and fastener rows perpendicular to steel deck ribs. Exception: for Class 1-75
and below, fastener rows and batten bars can be installed parallel to the building edge within the defined
building perimeter width if:
a) the distance between fastener rows in this area is ≤ 3 ft (0.9 m), and
b) two FM Approved deck fasteners or minimum 5⁄8 in. (16 mm) diameter welds are installed through each
lower deck flange (every 6 in., 150 mm on center)
2.2.7.3.3 Where acceptable to the roof cover manufacturer, in lieu of seaming numerous partial single-ply
membrane sheets in the rake areas, an FM Approved batten bar may extend across the perimeter width,
midway between rows of fasteners and be fastened to the deck. Adhere a membrane strip of a minimum width
as recommended by the manufacturer over the batten bar and the edges caulked to maintain water-tightness,
if needed. Similar enhancements may be provided in the corner areas using two intermediate batten bars.
2.2.7.3.4 Provide deck securement as follows when the FM Approved (field-of-roof) spacing between rows of
roof cover fasteners exceeds 6 ft (1.8 m):
a) Use only FM Approved deck fasteners to secure the deck. Ensure the spacing within rows of deck
fasteners in the field-of-roof does not exceed the spacing within rows of roof cover fasteners.
b) Double the deck fastening in the roof perimeter. For example, if roof cover fasteners are 12 in. (300
mm) on center in the field, provide deck fasteners 12 in. on center in the field (per a.) and provide deck
fasteners at 6 in. (150 mm) centers in the perimeter. If cover fasteners are 6 in. (150 mm) on center in
the field, provide deck fasteners at 6 in. centers in the field (per a.) and provide two deck fasteners at 6
in. (150 mm) centers in the perimeter.
c) In corner areas, use the same number of deck fasteners as for the perimeter, but with ¾ in. diameter
washers. Ensure washers are carbon steel with a 0.328 in. (8.4 mm) center hole and are minimum 0.065
in. (1.6 mm) thick.
2.2.7.4 Ballasted Single-Ply Membrane: Design Recommendations
2.2.7.4.1 Do not use stone-ballasted roofs on buildings taller than 150 ft (46 m) high, or in areas with design
wind speeds ≥ 100 mph (45 m/s) (See Data Sheet 1-28, Wind Design) or beyond the acceptable limits of
Tables 2 or 3. These limitations do not apply to paver ballasted systems.
2.2.7.4.2 To ensure the quality of the materials, component compatibility, and Class 1 undeside fire exposure
ratings, ensure individual components in ballasted systems are FM Approved for use in combination.
Typically, the combination would be FM Approved for adhered or mechanically attached applications. Use only
FM Approved membranes in ballasted applications.
2.2.7.4.3 Ensure stone ballast in loose-laid systems is clean, smooth, well-rounded gravel meeting the
gradation requirements of Standard Size No. 3 for Coarse Aggregate per ASTM D448 (nominal 1 to 2 in.
[25 to 50 mm] diameter).
2.2.7.4.4 Ensure the density of stone ballast is approximately 165 pcf (2650 kg/m3
). Do not use lightweight
stone such as limestone.
2.2.7.4.5 Apply stone ballast per Table 2 or 3. Install paver blocks per Tables 4 to 7. Ensure square edge
pavers are a minimum of 1 ft2
(0.1 m2
). Ensure beveled/strapped pavers are a minimum of 0.89 ft2
(0.08 m2
)
(8 × 16 in., [203 × 404 mm]). All weights are the minimum recommended weights.

2.2.7.4.6 For ballast application only, the roof perimeter and corners are subject to a minimum dimension
of 8.5 ft (2.6 m) rather than 4 ft (1.2 m) as defined in Data Sheet 1-28, Wind Design. Also, the 10% lesser
building plan dimension limit is not applied in determining the corner dimension. The 4 ft (1.2 m) minimum
and the 10% limit still apply to roof deck securement.
2.2.7.4.7 The structure must be capable of supporting the dead weight of the roof system and ballast without
encroaching on live load capacity or creating or aggravating a ponding problem. Have the load capacity of
the roof verified by a registered civil or structural engineer.
2.2.7.4.8 The roof slope should be ≤ 10°, 2 in./ft (167 mm/m).
2.2.7.4.9 Stone ballast can be used in the roof field with pavers used at the perimeter and corners, provided
the appropriate weights of stone and pavers are used in each area.
2.2.7.4.10 Ensure flashing systems used with pavers secure the pavers at the building edge.
2.2.7.5 Ballasted Single-Ply Membrane—Installation Recommendation
2.2.7.5.1 Extreme care is needed when transporting ballast to the roof. Stop the conveying machine if ballast
begins to pile up. Distribute ballast to the specified weight before restarting the conveying machine.
2.2.7.6 Ballasted Single-Ply Membrane—Maintenance Recommendation
2.2.7.6.1 Inspect ballasted roofs semi-annually and after storms. Redistribute scoured ballast. Gravel scour
greater than 50 ft2
(5 m2
) is considered excessive. See Data Sheet 1-30, Repair of Wind Damaged Roof
Systems, for action to be taken if this type of damage occurs.
Table 2. Weight Needed of No. 3 Round Stone Ballast, Parapet ≤ 36 in. (914 mm)
Uplift Pressure
(psf) Data
Sheet 1-28
Ballast Weight, (psf)
Steel or Pre-Cast Panel Deck Cementitious Wet Fill Deck
Field Peri. Cors. Field Peri. Cors.
≤ 20 10 12 15 10 10 10
21 to 25 12 15 15 10 12 12
26 to 30 12 15 18 12 12 15
31 to 35 Use FM Approved 1-90 System 12 15 18
36 to 45 Use FM Approved 1-90 System Use FM Approved 1-90 System
Table 3. Weight Needed of No. 3 Round Stone Ballast, Parapet > 36 in. (914 mm)
Uplift Pressure
(psf) Data
Sheet 1-28
Ballast Weight, psf
≤ 20 10 10 12 10 10 10
21 to 25 12 12 12 10 10 12
26 to 30 12 12 15 12 12 12
31 to 35 12 15 18 12 12 15
Table 4. Weight Needed of Paver Blocks—not T&G, Beveled or Strapped to Each Other, Parapet ≤ 36 in. (914 mm)
Uplift Pressure
(psf) Data
Sheet 1-28
Paver Weight, psf
≤ 15 12 12 15 12 12 12
16 to 20 12 15 20 12 12 15
21 to 25 12 18 23 12 15 18
26 to 30 15 23 30 12 18 21

Table 5. Weight Needed of Paver Blocks—not T&G, Beveled or Strapped to Each Other, Parapet > 36 in. (914 mm).
Uplift Pressure
(psf) Data
Sheet 1-28
Paver Weight, psf
≤ 15 12 12 12 12 12 12
16 to 20 12 12 15 12 12 12
21 to 25 12 15 18 12 12 15
26 to 30 15 18 21 12 15 18
Table 6. Weight Needed of Paver Blocks—T&G, Beveled or Strapped to Each Other, Parapet ≤ 36 in. (914 mm)
Uplift Pressure
(psf) Data
Sheet 1-28
Paver Weight, psf
≤ 15 12 12 12 12 12 12
16 to 20 12 12 15 12 12 12
21 to 25 12 15 15 12 12 12
26 to 30 12 15 18 12 12 15
31 to 35 15 18 18 12 15 18
Table 7. Weight Needed of Paver Blocks—T&G Beveled or Strapped to Each Other, Parapet > 36 in. (914 mm)
Uplift Pressure
(psf) Data
Sheet 1-28
Paver Weight (psf)
≤ 15 12 12 12 12 12 12
16 to 20 12 12 12 12 12 12
21 to 25 12 12 12 12 12 12
26 to 30 12 12 12 12 12 12
31 to 35 15 15 18 12 12 12
36 to 45 15 18 18 12 12 12
Notes:
1. For all tables, to convert to kg/m2
, multiply by 4.88.
2. Uplift pressure is that determined from Data Sheet 1-28, Wind Design, and is not factored.
2.2.8 Asphalt and BUR Installation Recommendations
2.2.8.1 Locate heating kettles so that buildings and combustibles will not be exposed.
2.2.8.2 Apply asphalt at the equiviscous temperature (EVT) ± 25°F (± 14°C). Ensure asphalt is not
continuously heated to or above the blowing temperature. These temperature limits are generally supplied
by the manufacturer.
2.2.8.3 Immediately roll felt into the asphalt. If the roll veers off line, cut it and start again. Broom organic
felts in place.
2.2.8.4 Keep rolls of felts dry and store on end.
2.2.9 Roof Covers Adhered to Mechanically Attached Base Sheets—Fastener Installation
Recommendations
2.2.9.1 Increase the number of fasteners securing the base sheet over the FM Approved roof field spacing
by 70% in the perimeter and 160% in the corners. For mod bit base plies secured to steel deck roofs, see
recommendation 2.2.7.3. For other deck types and uniformly reinforced base plies, determine fastening
density on a unit area per fastener basis.

2.2.9.2 Ensure fasteners for lightweight insulating concrete are not closer than 4 in. (102 mm) on-center, to
avoid cracking the deck.
2.2.9.3 For base sheets only, fastening increases can be obtained by adding rows of fasteners and/or
additional fasteners along each row.
2.2.10 Liquid Applied Roof Covers—Installation Recommendations
2.2.10.1 At the end of each work day, spray-in-place polyurethane must be protected with the coating. At a
minimum, apply the base coat at the end of each day. The foam will be degraded by UV radiation without
the coating.
2.2.10.2 Ensure the roof surface is clean and dry prior to applying polyurethane foam or coating.
2.2.11 Mechanically Fastened Base Sheet Assemblies Over Wood Decks—Design and Installation
Recommendations
Currently, there are no FM Approved combinations of a base sheet mechanically fastened directly to a wood
deck followed by a BUR or modified bitumen cover. These assemblies are popular in some regions. They
are considered Class 2 and need automatic sprinkler protection regardless of the FM Approval status of the
deck. They can be acceptable from a wind resistance viewpoint if installed in accordance with this section.
Table 8. Base Sheet Fastener Coverage for Non-FM Approved Combinations, ft2
per Fastener
Field of
Uplift
Pressure
(Data
Sheet
1-28
< 21 psf
(< 1.0 kPa)
21-30 psf
(1.0-1.4 kPa)
31-45 psf
1.48-2.15 kPa)
Roof Area Field Peri. Cors. Field Peri. Cors. Field Peri. Cors.
Fastener
Strength,
lb(N)
30(135)
40(180)
50(220)
60(265)
70(310)
80(355)
90(400)
100(445)
110(490)
120(535)
140(625)
160(710)
0.75
1.00
1.25
1.50
1.75
2.00
2.00
2.00
2.00
2.00
2.00
2.00
0.43
0.57
0.71
0.86
1.00
1.14
1.29
1.43
1.57
1.71
2.00
2.00
0.29
0.38
0.48
0.57
0.67
0.76
0.86
0.95
1.05
1.14
1.33
1.52
—
—
—
1.00
1.16
1.33
1.50
1.67
1.83
2.00
2.00
2.00
—
—
—
0.57
0.67
0.76
0.86
0.95
1.05
1.14
1.33
1.52
—
—
—
0.39
0.45
0.52
0.58
0.65
0.71
0.77
0.90
1.03
—
—
—
—
—
—
1.00
1.11
1.22
1.33
1.56
1.78
—
—
—
—
—
—
0.56
0.63
0.69
0.75
0.86
1.00
—
—
—
—
—
—
0.38
0.43
0.47
0.51
0.60
0.68
1. To convert to m2
per fastener, multiply by 0.0929.
2. When coverage is less than 0.50, a stronger fastener is suggested. Ensure coverage does not exceed 2.00 unless FM Approved.
3. Less than 40 lb (180 N) pull-out per fastener may indicate unsound deck or improper fastener. Consult manufacturer’s specifications.
4. If the building has a minimum 3 ft (0.9 m) high continuous parapet and the roof slope is ≤ 10° (167 mm/m), the corner areas may be
fastened in the same manner as the perimeter.

Table 9. Standard 36 in. (0.9 m) Base Sheet Fastening (Non-FM Approved Components). (See Fig. 8.)
Fastener Coverage,
ft2
/fastener
(Table 8)
Maximum Fastener Spacing, in. (mm) On Center
One Intermediate Row Two Intermediate Rows
At Laps Between Laps At Laps Between Laps
0.30-0.50
0.51-0.70
0.71-0.90
0.91-1.10
1.11-1.30
1.31-1.50
1.51-1.75
1.76-2.00
2.01-2.50
2.51-3.00
3.01-4.00
—
4 (102)
5 (127)
6 (152)
8 (203)
10 (254)
12 (305)
12 (305)
12 (305)
12 (305)
12 (305)
—
7 (179)
12 (305)
14 (356)
14 (356)
14 (356)
16 (406)
20 (508)
24 (609)
24 (609)
24 (609)
4 (102)
5 (127)
7 (179)
8 (203)
10 (254)
12 (305)
12 (305)
—
—
—
—
6 (179)
11 (279)
13 (330)
16 (406)
20 (508)
22 (559)
22 (609)
—
—
—
—
Fig. 8. Fastener layout for 36 in. (914 mm) wide base sheet.

Table 10. Minimum Metal Disk or Fastener Head Size (Base Sheet Fasteners)
Fastener Pull-Out Strength, lb (N) Minimum Disk/Head Diameter, in. (mm)
< 45 (200)
45-60 (200-265)
61-70 (270-310)
71-80 (315-355)
81-100 (360-445)
101-120 (450-535)
> 120 (535)
1.00 (25)
1.25 (32)
1.50 (38)
1.75 (44)
2.00 (51)
2.50 (64)
3.00 (76)
2.2.11.1 Perform field pull-out tests of the proposed base sheet fastener to determine pull-out performance.
Base sheet fastener spacing and head or disk size is then determined per Tables 8, 9, and 10. An example
calculation is given below.
2.2.11.2 Ensure base sheet fasteners have metal heads or disks.
2.2.11.3 Where non-FM Approved wood roof decks have been used and an FM Approved roof system
(above-deck components) is installed, roof system fastening can be in accordance with the Approval Guide
listings for FR-treated wood decks, provided the deck is nominal 3⁄4 in. (19 mm) thick plywood or nominal
2 in. (51 mm) thick lumber. If a thinner deck is used, fastener pull-out tests are needed. Determine the fastener
density per section 2.2.4.1.3.
Example Problem: Wood Deck, Nailed Base Sheet:
Given: The field-of-roof uplift pressure (See Data Sheet 1-28, Wind Design) is 28 psf (1.35 kPa) and the
fastener pull-out strength is 120 lb (535 N). From Table 8, 10th line (120 lb, 535 N), select maximum coverage
area per fastener as follows:
Roof field = 2.00 ft2
(0.2 m2
) Roof perimeter = 1.14 ft2
(0.1 m2
) Roof corners = 0.77 ft2
(0.07 m2
)
From Table 9, select base sheet fastener spacing:
Area At Laps Between Laps
Roof field 12 in. (305 mm) 20 in. (508 mm)
Perimeters 8 in. (203 mm) 14 in. (356 mm)
Corners 5 in. (127 mm) 12 in. (305 mm)
Per Table 10, the fastener head or disk size needs to be at least 2.5 in. (64 mm) in diameter.
2.2.13 Roof Deck Span and Securement for Wind Loads
2.2.13.1.1 Use FM Approved steel deck for all insulated steel deck roofs. Do not use the deck at spans greater
than FM Approved. The FM Approved spans are measured center-to-center. For new construction, ensure
the deck span is adequate for wind pressures in all roof areas, including the perimeter and corner areas (see
DS 1-28 and examples in section 3.1.10), taking into consideration the following (unless specifically tested
and FM Approved):
• For roofs with proposed spans and wind design pressures exceeding Table 11, or where a large spacing
between rows of fasteners for mechanically fastened roof covers results in large concentrated loads (as
noted below or defined by the RoofNav listing), this may necessitate the use of steel deck with higher yield
strength or spans less than the FM Approved maximum limit as noted below may be necessary.
• Use Grade 80 (FY = 80,000 psi), wide rib, minimum 22 ga. (0.0295 in., 0.749 mm) steel deck with a
maximum span of 6 ft (1.8 m) when roof systems need an FM Approval rating higher than 1-90, or when
the spacing between rows of roof cover fasteners is greater than 6 ft (1.8 m).
• When the FM Approval rating needed for the field of the roof is higher than 1-135, use minimum 22 ga.
(0.0295 in., 0.749 mm), Grade 80 (FY = 80,000 psi), wide rib steel deck. Also, in corner areas, either use
spans less than 6 ft (1.8 m), or 20 ga. (0.0358 in., 0.909 mm) or 18 ga. (0.0474 in., 1.204 mm) deck as
needed per Table 11 and as adjusted to reflect the higher grade of steel.

• Use Table 11 to ensure the allowable wind uplift pressure resistance of the deck is not exceeded.
• Use enhanced deck securement for areas with higher wind design pressures as defined by 2.2.13.1.4.
Table 11. Allowable2
Uniform Uplift Pressure (Notes 1,3,4,5)
ALLOWABLE UNIFORM UPLIFT PRESSURE (psf) FOR GRADE 33 (Fy = 33,000 psi) STEEL ROOF DECK
1.5″ Type B — WIDE RIB (WR)
Span
Type
Gage SPAN
4’-0’’ 4’-6‘‘ 5’-0’’ 5’-6‘‘ 6’-0’’ 6’-6‘‘ 7’-0’’ 7’-5’
SINGLE 22 207 164 132 109 92
20 267 211 171 141 119 101
18 356 281 228 188 158 135 116 103
DOUBLE 22 205 162 131 108 91
20 254 201 163 134 113 96
18 345 273 221 183 154 131 113 100
TRIPLE 22 256 202 164 135 114
20 318 251 203 168 141 120
18 432 341 276 228 192 163 141 125
1.5‘‘ Type F- INTERMEDIATE RIB (IR)
Span
Type
Gage SPAN
4’-0’’ 4’-6‘‘ 4’-11’’ 5’-0‘‘ 5’-5’’ 5’-6‘‘ 5’-9’’ 6’-0’ 6’-3‘‘
SINGLE 22 124 98 82
20 151 119 100 96 82
18 199 157 132 127 108 105 96 89 82
DOUBLE 22 115 91 76
20 143 113 94 91 78
18 195 154 129 125 106 103 94 87 80
THREE
OR
MORE
22 143 113 95
20 179 141 118 114 97
18 243 192 161 156 133 129 118 108 100
1.5’’ Type A – NARROW RIB (NR)
SPAN
TYPE
Gage SPAN
4’-0‘‘ 4’-3’’ 4’-6‘‘ 4’-9’’ 5’-0‘‘ 5’-3’’ 5’-6‘‘ 5’-9’ 6’-0’’
SINGLE 22 110 98 87 78
20 133 118 105 94 85 77
18 177 156 140 125 113 103 93 85 79
DOUBLE 22 100 89 79 71
20 125 111 99 89 80 72
18 171 151 135 121 109 99 90 83 76
THREE
OR
MORE
22 125 111 99 89
20 156 138 123 111 100 91
18 214 189 169 152 137 124 113 103 95

ALLOWABLE UNIFORM UPLIFT PRESSURE (psf) FOR GRADE 33 (Fy = 33,000 psi) STEEL ROOF DECK
3‘‘ Type N – DEEP RIB (3DR)
SPAN
TYPE
Gage SPAN
7’-0’’ 7’-6‘‘ 8’-0’’ 8’-6‘‘ 9’-0’’ 9’-6‘‘ 10’-0’’ 10’-6’ 11’-0‘‘
SINGLE 22 136 118 104 92 82 74 66 60 55
20 165 144 126 112 100 90 81 73 67
18 218 190 167 148 132 118 107 97 88
DOUBLE 22 118 103 90 80 71 64 58 52 48
20 147 128 113 100 89 80 72 65 60
18 202 176 155 137 122 110 99 90 82
THREE
OR
MORE
22 147 128 113 100 89 80 72 66 60
20 184 160 141 125 111 100 90 82 74
18 253 220 193 171 153 137 124 112 102
Notes for Table 11:
1. This table includes a 1⁄3 increase in normal allowable stress. It should be used specifically for wind and should not be used to determine
gravity load resistance.
2. Compare the values in this table to design pressures per DS 1-28. Do not apply a safety factor to the design pressures as one is
included in this table.
3. Table 11 is based on a yield stress (Fy) of 33,000 psi. For higher strength steels the allowable wind uplift pressure may be determined
by multiplying the values in Table 11 by 1.15 when Fy = 40,000 psi (276 mPa), by 1.35 when Fy = 50,000 psi (345 mPa) and by 1.55 when
Fy ≥ 60,000 psi (415 mPa). These multipliers take into consideration both the increase in strength due to Fy and the decrease in strength
due to deformation at higher stresses, so the relationship between yield strength and allowable pressure is not linear.
4. Interpolation by proportioning the square of the spans is most accurate; however, linear interpolation is reasonably accurate for these
span increments.
5. Where the recommended deck design pressure exceeds the capacity shown in Table 11, assemblies in which the combination of
above-deck components and securement act compositely with the deck may be accepted provided they have been satisfactorily tested.
In addition to the recommendations below, for mechanically attached single-ply membranes and
multi-ply covers with mechanically attached base sheets, also refer to section 2.2.7.3.
2.2.13.1.2 Secure steel deck to supports for Class 1-90 and below, (unfactored design pressure ≤ 45 psf)
as follows:
• Space FM Approved deck fasteners or welds a maximum of 12 in. (305 mm) on center (every other rib
for 11⁄2 in. [38 mm] deck) at all supports in the field of the roof.
• Space FM Approved deck fasteners or welds a maximum of 6 in. (152 mm) on center (every rib for 11⁄2 in.
[38 mm] deck) at all supports in the roof corners and perimeter.
• For Class 1-75 and 1-90 (field rated) construction, use FM Approved deck fasteners or minimum 5⁄8 in.
(16 mm) diameter welds in the field and perimeter; and use either one FM Approved deck fastener or two
welds in each rib in the corner area.
• For Class 1-60 (field rated) construction, use FM Approved deck fasteners or minimum 1⁄2 in. (13 mm)
diameter welds in the field and perimeter, and use FM Approved deck fasteners or minimum 5⁄8 in. (16 mm)
diameter welds in the corners.
• Secure the deck to supporting members at each deck side lap, regardless of resultant weld spacing.
• For interlocking-type side laps (Fig. 9a), secure both sides of the lap (upper and lower).
• For overlap-type side laps (Fig. 9b), ensure securement penetrates all deck panels at the laps.
2.2.13.1.3 When Steel Deck Institute (SDI) deck-weld patterns are specified for use with 11⁄2 in. (38 mm)
deck, 24/3 or 36/4 patterns are acceptable where a maximum 12 in. (300 mm) weld spacing is recommended
and 24/5, 24/7, 30/6, 30/8, 36/7 or 36/9 patterns are acceptable where a maximum 6 in. (150 mm) weld
spacing is recommended.

2.2.13.1.4 If the recommended field of roof wind rating exceeds Class 1-90 (unfactored design pressure >
45 psf), or if the FM Approved field-of-roof deck fastening requires fasteners/welds at every rib, secure each
rib in the field of the roof. For corner and perimeter areas, enhance deck securement using one or more
of the following:
• Two FM Approved deck fasteners per rib (see Fig. 10)
• Shorter spans, yielding an equivalent increased fastening density
• Use 3⁄4 in. (19 mm) diameter, (0.328 in. [8.4 mm] diameter center hole; 0.065 in. [1.6 mm] minimum
thickness), carbon steel washers with deck fasteners in corner areas whenever the recommended field of
roof rating exceeds 1-135, or when the combination of needed wind rating and roof cover fastener row
spacing for mechanically fastened single plies (MFSP) warrants it. When this method is used, and the
thickness of the steel purlin is less than 1⁄8 in. (3.5 mm) the designer should ensure fastener pullout
resistance from the purlin is not exceeded.
See Section 3.1.10 for an example.
2.2.13.1.5 Provide mechanical fastening at all deck side laps as follows, unless the specific FM Approval
listing requires a closer spacing:
• Class 1-90 or lower: Ensure spacing between each side lap fastener or side lap fasteners and supports
is no more than 36 in. (0.9 m) in the field of the roof and no more than 30 in. (0.76 m) on center in the
perimeter and corner areas.
• Class 1-105 through 1-120: Ensure side lap fastening is no more than 30 in. (0.76 m) on center in the
field of the roof, and no more than 15 in. (0.38 m) on center in the perimeter and corners.
• Class 1-135 and higher: ensure side lap fastening is no more than 24 in. (0.61 m) on center in the field
of the roof, and no more than 15 in. (0.38 m) on center in the perimeter and corners.
• Fasten overlap-type side laps with FM Approved side lap fasteners.
• Interlocking-type laps can be fastened by button punching in Class 1-90 and lower.
• Do not weld side laps.
2.2.13.1.6 Ensure steel deck end laps are a minimum of 2 in. (51 mm). No additional fastening over that
noted above is needed for end laps. Consider specifying wider (4 in., 102 mm) end laps in the design. This
will make proper field installation easier by compensating for manufacturing and construction tolerances.
Fig. 9a. Side lap fastening: interlocking seam.
Fig. 9b. Side lap fastening: overlap seam.

2.2.13.1.7 For new construction, the structural design engineer of record is responsible for determining if
more stringent design criteria is needed with regard to the deck type and securement, such as providing
design diaphragm resistance in conjunction with wind uplift resistance.
2.2.13.2.1 Place steel deck true and straight so edges of insulation boards will not gradually ‘‘move off’’ the
deck flanges as the boards are installed.
2.2.13.2.2 Ensure workers stand on the upper deck panel when fastening laps, otherwise permanent
deflection can occur. See Figures 9a and 9b.
2.2.14 Lightweight Insulating Concrete Roof Decks
2.2.14.1.1 When a lightweight insulating concrete (LWIC) roof assembly is to be used as part of a new roof
or re-roof in non-hurricane prone regions, ensure it is FM Approved for the specific wind pressure
recommended in the field of the roof, with prescriptive enhancements provided for the securement of base
sheets in the perimeter and corner areas in accordance with recommendation 2.2.7.2.1. For regions prone to
hurricanes, typhoons and tropical cyclones, ensure the entire LWIC system is FM Approved for the specific
wind pressure rating needed for the field, perimeter, and corner areas as noted in Table 1.
2.2.14.1.2 Ensure form deck securement is as follows:
• For FM Approved installations using 1.5 in. (38 mm) deep steel deck as the form deck, ensure it is
FM Approved steel deck, designed and installed in accordance with the Approval Guide listing,
FM Approvals RoofNav, and section 2.2.13.
Fig. 10. Two deck fasteners per support, one into each bar joist top flange.

• For installations using different form-deck profiles, ensure the deck is secured in the field of the roof in
accordance with the FM Approvals RoofNav listing. If form deck perimeter and corner fastener density
is not specified in the FM Approvals RoofNav then ensure it is in accordance with section 2.2.1.5.6. In
addition, for roof corners in all construction and roof perimeters in Class 1-75 and above, ensure the
maximum distance between welds or fasteners at each supporting member is 4 in. (102 mm), regardless
of the load per weld.
2.2.14.1.3 Ensure all welding on deck less than 22 ga. (0.0295 in., 0.749 mm) incorporates minimum 3⁄8 in.
(9.5 mm) hole weld washers.
2.2.14.1.4 Ensure all form decks are of galvanized steel. Do not use aluminum alloy coatings.
2.2.14.1.5 Provide mechanical fastening at all form deck side laps. Ensure side lap fastener spacing is in
accordance with section 2.2.13.1.5.
2.2.14.2 Installation Recommendation
2.2.14.2.1 When installing lightweight insulating concrete on the form deck, the thickness of the initial slurry,
prior to placing the expanded polystyrene (EPS) insulation, is critical. There must be sufficient lightweight
insulating concrete to ensure an adequate bond. Refer to the FM Approvals RoofNav.
2.2.14.2.2 Ensure the following is done in regions prone to hurricanes, typhoons, and tropical cyclones:
a) Have a waste container at the job site. Initial flow of LWIC should be into the waste container until it is
flowing properly and is free of excess water.
b) Pour samples for wet density, dry density, and compression tests just prior to pouring the actual LWIC
deck. Compare wet density results to manufacturer’s data immediately, and compare other test results
later when they become available.
c) For mechanically fastened (MF) base sheets, conduct pull-out tests on base sheet fasteners after the
deck has set (2-3 days), but just before the base sheet is secured.
2.2.14.2.3 Ensure fasteners driven into lightweight insulating concrete are not closer than 4 in. (102 mm)
on center, to avoid cracking the deck.
2.2.15 Cementitious Wood Fiber Roof Deck Recommendations
2.2.15.1 Ensure deck securement in the field of the roof is in accordance with the RoofNav listing.
2.2.15.2 For decks that are through-fastened to supports, increase the number of fasteners securing the
deck in the perimeter and corners in accordance with, section 2.2.1.5.6.
2.2.15.3 For decks secured with clips at the side laps, use one of the following methods to increase fastening
at the corner and perimeter areas:
• The number of clips can be increased in accordance with section 2.2.1.5.6 by installing additional supports
to accommodate the additional clips.
• Additional securement can be obtained by installing through-fasteners in the corners and perimeter in
accordance with section 2.2.15.2 above. Determine the number of additional fasteners assuming the deck
was secured with these fasteners in the field of the roof.
2.2.16 Lumber and Plywood Deck
2.2.16.1 Recommendations
2.2.16.1.1 Use FM Approved fire-retardant (FR) treated lumber and plywood for all new wood roof deck
construction. FM Approved lumber is minimum 1.5 in. (38 mm) thick (nominal 2 in. [51 mm]) and FM Approved
plywood is minimum 23/32 in. (18 mm) thick (nominal 3⁄4 in. [19 mm]).
2.2.16.1.2 Where non-FM Approved wood roof decks have been used, roof deck fastening to resist anticipated
wind loads can be as outlined below.

Note: If the deck is thinner than the minimum FM Approved thicknesses, above-deck fastener pullout tests
are needed, as all above-deck fastening Approvals are based on the minimum FM Approved thickness. Refer
to section 2.2.5.2.6 for details on fastener pullout tests. In no case should plywood roof deck be thinner than
19⁄32 in. (15 mm) [nominal 5⁄8 in. (16 mm)].
2.2.16.1.3 Above-deck components on wood decks are currently FM Approved only for up to Class 1-90.
Hence, deck fastening recommendations are for these uplift ratings only.
2.2.16.1.4 Ensure plywood fastening is as follows:
• Deck panels are staggered in one direction.
• Fastening is based on 2 ft (0.6 m) span, with panel ends supported. Refer to RoofNav for guidance on
FM Approved plywood deck fasteners. Where not available nail per guidelines below.
• For nominal 5⁄8 in. (16 mm) thick deck, minimum 8d nails are used. For thicker decks, minimum 10d nails
are used.
• Smooth shank nails are acceptable for all fastening except roof corners in Class 1-75 and 1-90, where
ring shank nails are needed.
• For Class 1-60, field-of-roof nails are installed 6 in. (152 mm) on center at plywood panel end supports,
and 12 in. (304 mm) on center at all intermediate supports.
• For Class 1-60 perimeter and corners, and Class 1-75 and 1-90 across the entire roof, nails are installed
6 in. (152 mm) on center at all supports.
2.2.16.1.5 Ensure nominal 2 in. (51 mm) lumber fastening is as follows:
• Determine the design wind load and multiply by the tributary area of the nail, to determine the design load
on the nail.
• Determine nail penetration into support.
• Determine nail pullout strength by multiplying penetration length by appropriate value in Table 12 below.
Table 12. Nail pullout strength per in. (25 mm) of penetration
Nail Size (pennyweight) Pullout Resistance per in. (25 mm) of embedment, lb (N)
12d 28 (125)
16d 31 (138)
20d 36 (160)
30d 39 (173)
• Ensure pullout strength is at least twice the design load for the nail.
• Increase fastening at the roof perimeter and corners per section 2.2.1.5.6.
2.2.17 Structural Concrete Roof Deck Recommendations
2.2.17.1 Cast-in-place and precast structural concrete decks are acceptable in all wind exposures provided
the appropriate above-deck system is used (See Table 1). Use assemblies that are FM Approved over
concrete deck with wind uplift pressure ratings adequate for all areas including the perimeter and corners.
For roof systems using mechanically fastened insulation, see 2.2.1.5.1.
2.2.17.2 Ensure securement of precast structural concrete panels is designed by a professional civil or
structural engineer (PE). Deduct no more than 90% of the dead weight of the panels when calculating the
fastening needed for wind uplift resistance.
2.2.18 Torch Application of Modified Bitumen Roof Covers
2.2.18.1 Safely install torch-applied roof covers to prevent ignition of the roof assembly. Follow guidelines
in FM Global DS 1-33, Safeguard Torch-Applied Roof Installations.
2.2.18.2 Install torch-applied covers properly to ensure adequate adhesion and wind uplift resistance.
Consider the following where practical and safe:

a) The torch applicator should face the leading edge of the roll and pull the roll toward them. Walking
behind the roll and pushing the roll results in an improper angle for torch flame impingement onto the roll,
and results in damage to the cover from walking on the heated and softened sheet layer.
b) Pass the torch flame back and forth across the leading edge of the roll, with most of the flame impinging
on the leading edge of the roll, and only slight heating of the substrate below.
c) Do not overheat the roll, such as to cause excessive smoke.
d) Allow the bitumen to pool slightly at the leading edge of the roll across its entire width, allowing the
pool to flow very slightly beyond the edge of the roll as the sheet is unrolled (see Fig. 11).
2.2.19 Field Wind Uplift Tests
2.2.19.1 Conduct field uplift tests at FM Global insured client locations where practical, on all new, re-roofed
or re-covered roof installations in hurricane-prone regions where the basic wind speed is at least 100 mph
(45 m/s), except where otherwise noted in DS 1-52, Field Uplift Tests. Conduct tests in accordance with
DS 1-52.
2.2.20 Cold-Process Adhesives
2.2.20.1 Plan roof installations in locations that are prone to hurricanes or tropical cyclones and that use
cold-process adhesives to allow adequate curing time prior to potential exposure from a tropical cyclone. Also,
see section 3.1.2.2.
2.2.21 Fiberglass Reinforced Plastic (FRP) Roof Deck
2.2.21.1 Recommendations
2.2.21.1.1 Ensure the deck is secured in the field of the roof in accordance with the FM Approvals RoofNav
listing.
Fig. 11. Torch application of upper ply to a mechanically fastened base sheet — Note adhesive pooling at the leading
edge of the roll.

2.2.21.1.2 If deck perimeter and corner fastener density is not specified in the FM Approvals RoofNav, then
ensure it is in accordance with section 2.2.1.5.6.
3.0 SUPPORT FOR RECOMMENDATIONS
3.1 Supplemental Information
3.1.1 Class 1 and 2 Roof Decks
In 1953, a serious fire occurred in which fire spread along the underside of the insulated steel roof deck of
a large industrial facility. There were few combustibles in the building. The fire started at floor level and
heated the underside of the deck. Hot gases (from combustible above-deck components) were forced down
through the deck joints and became ignited. The fire continued to feed on the hot gases and spread along
the underside of the roof throughout the building. The entire building and contents were lost.
Such losses led to the development of the FM Approved Class 1 insulated steel deck roof, in which only
insulations of relatively low combustibility, used with restricted quantities of adhesive, were recommended.
As a result, fire losses from the burning of insulated steel deck roofs have decreased significantly.
The use of mechanical fasteners, as opposed to adhesives, to secure materials to the deck, further decreases
the fire hazard of newly constructed roofs. It should be noted that many Class 2 roofs are still in existence.
Loss experience involving Class 2 insulated steel deck in recent years has been favorable because most
are protected with sprinklers.
While flammable gases are liberated from both Class 1 and 2 roof decks, there are sufficient combustibles
only in Class 2 roof decks to produce a self-propagating fire across the roof underside. The fire propagates
without additional heat input from the occupancy fire. This can result in complete destruction of the building
contents. Sprinkler protection or an FM Approved roof deck undercoating is needed to prevent fire spread
under Class 2 roofs.
Class 2 steel deck roofs can be upgraded to Class 1 by one of two methods:
(1) Remove all above-deck components, including asphalt, down to the deck and mechanically fasten a roof
system that is FM Approved for new construction on the deck.
(2) Apply an FM Approved roof deck undercoating to the entire steel deck underside. These coatings enable
Class 2 roof decks to meet the heat release rate limits of Class 1 roofs. Under-coatings are only FM Approved
and recommended for use on steel decks.
If the combustibility of an existing roof deck is not known, a Class 1 or 2 rating can be determined by cutting
out a sample for testing. For details, refer to Data Sheet 1-5, Removal and Shipping Roof Deck Samples
for Calorimeter Testing.
3.1.2 Wind Uplift Resistance, Non-Ballasted Roof Covers
3.1.2.1 Perimeter and Corner Enhancements for Mechanically Fastened, Multi-Ply Roof Covers
For a mechanically attached roof ensure cover the spacing between rows of fasteners does not exceed
60% of the spacing (of that FM Approved for the field of roof [FOR] rating) in the perimeter and 40% in the
corners. This accounts for the higher pressure coefficients in those areas (1/0.6 = 1.67, 1/0.4 = 2.5). From
a practical standpoint, for a multi-ply cover that is FM Approved when fastened in or through the seams only,
that would relate to adding one intermediate row of roof cover fasteners in the perimeter and two intermediate
rows in the corners. Rows of fasteners should run across the deck ribs to evenly distribute the wind loads
to points of deck securement. Spacing within rows can be the same throughout.
When the FOR FM Approved system already has one intermediate row and the spacing is 12 in. (300 mm)
in the seams and 12 in. (300 mm) in one staggered intermediate row. The average fastener spacing is about
1.5 ft2
(0.14 m2
) for the field, and should be no more than 0.90 ft2
(0.084) and 0.60 ft2
(0.056 m2
) in the
perimeter and corners, respectively. The spacing between fasteners in rows should be in multiples of 6 in.
in order to hit the top flanges of 1-1⁄2 in. (38 mm) deep steel deck. For the perimeter, the fasteners could
be placed 6 in. (150 mm) OC in the seams and 6 in. (150 mm) OC in the intermediate row (0.75 ft2
,
0.07 m2
). For the corners, the fasteners could be placed 6 in. OC (150 mm) in the seams and 6 in. (150
mm) OC in two intermediate rows (0.50 ft2
or 0.05 m2
per fastener).

When the FM Approved system to be used in the field of the roof already requires one or more intermediate
rows of roof cover fasteners, this becomes a little more complicated.
If the FOR FM Approved system already has two intermediate rows and the Approved spacing is 12 in. (300
mm) in the seams and 18 in. (450 mm) in two staggered intermediate rows, the average fastener spacing
is about 1.25 ft2
(0.12 m2
) for the field, and should be not exceed 0.75 ft2
(0.07 m2
) and 0.50 ft2
(0.05 m2
) in
the perimeter and corners, respectively. The spacing between fasteners in rows should be in multiples of
6 in. (150 mm) in order to hit the top flanges of 1-1⁄2 in. (38 mm) deep steel deck. For the perimeter, the
fasteners could be placed 6 in. OC (150 mm) in the seams and 12 in. (300 mm) OC in two staggered
intermediate rows, or 12 in. (300 mm) OC in the seams and in three staggered intermediate rows (0.75
ft2
or 0.07 m2
/fastener). If fasteners go thru both layers at the seam, then the latter alternative is
recommended. For the corners, the fasteners should be placed 6 in. (150 mm) OC in the seams and
6 in. (150 mm) OC in two intermediate rows (0.50 ft2
or 0.05 m2
per fastener).
An adhered roof covering obtains its uplift resistance from the tensile strength of the adhesive bond between
the roof cover and insulation. When failure occurs, the result will be separation from the material below, or
fractured insulation boards. Continuing uplift forces lead to peeling of the cover, which can result in the rapid
delamination of large areas of the roof covering.
FM Global research testing has shown that fastener placement on the insulation board has a significant effect
on the ultimate strength of the assembly. For example, research conducted with 4 × 4 ft × 1.5 in.
(1.2 × 1.2 m × 38 mm) polyisocyanurate insulation covered with a BUR showed a dramatic change in
performance simply by rearranging the fasteners on the boards. For both tests, the fastening density was
1 fastener per 1.78 ft2
(0.17 m2
). Figures 12a and 12b show the fastener placement for each test.
The test of pattern 12a failed at 105 psf (5.0 kPa) by fracture of the insulation board. The test of pattern
12b failed at 160 psf (7.6 kPa) by screws pulling out of the deck.
Mechanically attached single-ply membranes are secured by fasteners that directly engage the deck. This
results in a concentration of forces that are transmitted into the fastener. There also are high stresses in the
membrane at the fastener. If one fastener fails, the load will be transferred to adjacent fasteners, usually
causing these fasteners to be overstressed.
If fasteners are driven into the bottom flange of steel deck, the moment arm is at least 1.5 in. (38 mm) longer
(the depth of steel deck) than with top flange engagement. This longer moment arm can result in increased
fastener back-out and failure.
3.1.2.2 Cold Process Adhesives in Tropical Cyclone Exposed Areas
Fig. 12a/12b. 4 × 4 ft (1.2 × 1.2 m) insulation boards secured with nine fasteners per board.

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