Type IV or heavy timber construction uses large dimensional lumber for structural elements like walls, floors, and roofs to provide fire resistance. It was commonly used in the late 19th/early 20th century for industrial and commercial buildings. Key features include wood columns no less than 8 inches thick, wood girders at least 6 inches thick, and floor/roof planks at least 2 inches thick. Interior walls are also fire-resistant. This construction type is beneficial as it is stable during early-stage fires and the large timber sizes allow it to burn longer before collapse compared to other materials like steel.

1. Type IV
Building
Construction
By:
Manuel S.
Steven E.
Bryan W.
Jon M.

2. Type IV Building Construction
• Some times is called “mill construction” because
it was the type of construction used at the turn of
the century.
– Was used on New England mills to house heavy
equipment.
• These structures are manly used in
manufacturing centers, churches, and/or schools.
• Buildings have masonry walls like type III
buildings but the interior wood consists of large
timbers.
• The floor and roof are plank board

3. • In a heavy-timber building a wood column
cannot be less than eight inches thick in any
dimension and a wood girder cannot be less
than six inches thick.
• One difference between
a heavy timber building
and ordinary construction
is that a heavy-timber
building does not have
plaster walls and ceilings
covering the interior
wood framework.

4. • In heavy timber type of construction fire
resistance is attained by putting limitations of
minimum sizes on the wood structural
members and on minimum thickness and
composition of wood floors and roofs; by
avoiding of concealed spaces under floors and
roofs; by use of approved fastenings,
construction details, and adhesives; and
providing the required degree of fire
resistance in exterior and interior walls.

5. • Interior load-bearing walls will be of noncombustible
materials similar to the exterior walls and play a critical
role both in fire separation
• Typically, the walls are 24 to 36 inches thick at ground
level
• Heavy-Timber or Type IV buildings will have four
bearing exterior walls made from noncombustible
materials.

6. Types of Failures/Precautions
• Masonry Wall Collapse - which consist of…
• Inward/Outward

7. • 90 degree outward

8. • Curtain Wall

9. • Parapet Wall Collapse(s)

10. Floor Failures….
• Pancake

11. • V-shaped

12. • Lean-to

13. • ….and Tent.

14. • Roof Collapse

15. • Interior Wall Collapse

16. • Ceiling Collapse

17. • Use of unprotected
steel
– Unprotected steel can
fail early and trap
firefighters
• You must always
recognize the size,
use and age of the
building.

18. • Always respect the COLLAPSE ZONES.
– If the fire is suspected of collapsing then a
collapse zone must be established.

19. • Beams
– Penetrated for conduit and pipes.
– Long bolts and nuts are used.
– Metal can create a path for heat to reach the interior.
– Watch for spliced timber with overlapping joints and
metal connectors.

20. • This type of construction does not collapse during the early stages
of a fire when interior firefighting is taking place. However, after
several hours, its floors will collapse and the free-standing walls will
fall into the street and on to the roofs of lower buildings nearby.
• Conflagration breeder
– Structure that presents severe exposure problem that are capable of
starting a large, multiple building fires
• Characteristics of a conflagration breeder are radiant heat and fire brands,
large collapse zones, and fire spread.
• Expect the fight of your life

21. • Heavy timber is benefited by extended time of burning
and the lack of voids spaces.
• Heavy timbers perform well and do not fail early in a
fire, and is considered “slow burning”
– “slow burning” means “collapse resistant”
– Statement is only true when a fire department can
maintain an interior offensive operation.

22. When it was used
Developed since that time, the building method was
brought to North America in the 17th century by
European settlers.
Started in the 18th century, in the US, on the east
coast, and still stand to this day
The first completely self-supporting timber frame
structure is believed to have been constructed during
the 10th century.
The advancement of technology and design
improvements helped to revive North American heavy
timber framing in the 1970s.
In Europe, there is timber framed buildings
constructed over 500 years ago that are still standing
today.

23. Why is Type IV used?
• Positive aspect of these
buildings is that they are built
for strength, with heavy-
timber supports for the floor
and roof structure, providing a
strong and stable building in
the early stages of a fire.
• One advantage of this method
of construction was that very
little of the structure was
enclosed to create voids.
• Heavy timber construction is
known to be extremely stable
under fire conditions due to
the size of the load bearing
members with large columns
and roof support trusses

24. • The heavy timber building was a multistory building,
designed and originally used for storage and industrial
purposes.
• The thickness of heavy timber is built for strength,
which makes it able to burn for longer periods of time
• Large diameter wood components hold longer than
steel .
• Used in building moderate-priced factories,
warehouses, business blocks, and dwelling houses
because of its simplicity, strength, and the rapidity with
which it may be erected, and also because of its
adaptability to very fine architecture if the designer
uses judgment and skill.

25. How is it
used?
Roof Framing
— Wood-frame or glued-laminated arches for roof construction,
which spring from the floor line or from grade and do not
support floor loads, members not less than 6” nominal in
width and have less than 8“nominal in depth for the lower half
of the height and not less than 6“ nominal in depth for the
upper half. Framed or glued laminated arches for roof
construction that spring from the top of walls or wall
abutments, framed timber trusses and other roof framing,
which do not support floor loads, shall have members not less
than 4” nominal in width and not less than 6” nominal in
depth. Spaced members shall be permitted to be composed of
two or more pieces not less than 3“ nominal in thickness
where blocked solidly throughout their intervening spaces or
where spaces are tightly closed by a continuous wood cover
plate of not less than 2” nominal in thickness secured to the
underside of the members. Splice plates shall be not less than
3” nominal in thickness. Where protected by approved
automatic sprinklers under the roof deck, framing members
shall be not less than 3” nominal in width.

26. Floor Framing
— Wood beams and girders shall be of
sawn or glued-laminated timber and
shall be not less than 6” nominal in
width and not less than 10” nominal in
depth. Framed sawn or glued-laminated
timber arches, which spring from the
floor line and support floor loads, shall
be not less than 8” nominal in any
dimension. Framed timber trusses
supporting floor loads shall have
members of not less than 8” nominal in
any dimension.

27. • Floors
– Floors shall be without concealed spaces. Wood floors
shall be of sawn or glued-laminated planks, splined or
tongue-and-groove, of not less than 3” nominal in
thickness covered with 1” nominal dimension tongue-
and-groove flooring, laid crosswise or diagonally, or 0.5”
particleboard or planks not less than 4” nominal in width
set on edge close together and well spiked and covered
with 1” nominal dimension flooring or 15/32” wood
structural panel or 0.5” particleboard. The lumber shall
be laid so that no continuous line of joints will occur
except at points of support. Floors shall not extend closer
than 0.5” walls. Such 0.5” space shall be covered by a
molding fastened to the wall and so arranged that it will
not obstruct the swelling or shrinkage movements of the
floor. Corbeling of masonry walls under the floor shall be
permitted to be used in place of molding.
• Roofs
– Roofs shall be without concealed spaces and wood roof
decks shall be sawn or glued laminated, splined or
tongue-and-groove plank, not less than 2” thick, 1⅛”
thick wood structural panel (exterior glue), or of planks
not less than 3” nominal in width, set on edge close
together and laid as required for floors. Other types of
decking shall be permitted to be used if providing
equivalent fire resistance and structural properties.
• Columns
– Wood columns shall be sawn or glued laminated and
shall not be less than 8” nominal in any dimension where
supporting floor loads and not less than 6 inches (152
mm) nominal in width and not less than 8” nominal in
depth where supporting roof and ceiling loads only.
Columns shall be continuous or superimposed and
connected in an approved manner.
• Partitions(Walls)
– Partitions shall be of solid wood construction formed by
not less than two layers of 1” matched boards or
laminated construction 4” thick, or of 1-hour fire-
resistance-rated construction.
• Exterior structural members
– A horizontal separation of 20’ or more is provided, wood
columns and arches conforming to heavy timber sizes
shall be permitted to be used externally

28. • Lintels or arches to
transfer loads over
openings made from
materials of substantial
strength.

29. • Exterior wall construction are
usually noncombustible,
commonly brick, block, or
stone
• Common walls between
buildings and floor supports
seldom are used in heavy-
timber construction

30. End