Henry informational online course manage the moisture in exterior walls

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Henry Company
300 Industrial Drive
Fernley, NV 89408
Tel: 775-333-6400
Fax: 775-333-6411
Toll-Free: 800-773-4777
Email: scfhenry@henry.com
Web: www.henry.com
Manage the Moisture: Solutions for Exterior Walls

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Purpose and Learning Objectives
Purpose: Problems associated with moisture in construction are common and wide-ranging—from mold and rot, to
corrosion and degradation, to leakage and staining—and affect not just the durability, appearance, and functioning of the
building, but the health of the building’s occupants. This course addresses the materials and techniques that help to
manage moisture in exterior walls and includes examples of common mistakes that lead to failures.
Learning Objectives:
At the end of this program, participants will be able to:
• define moisture management and discuss its importance to occupant health, building durability, and lower costs
• describe the forms of moisture and how it moves in and around the exterior wall
• identify the building envelope materials that contribute to effective moisture management in exterior walls, and restate
the applicable testing and standards, and
• detect and avoid common failures in material selection and installation, and describe proper methods for both that will
mitigate future damaging and harmful moisture issues.

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Table of Contents
Introduction to Moisture Management
Moisture Management Materials for Exterior Walls
Installation Guidance and Methods
Epic Fails
Summary and Resources
Click on title to view

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Introduction to Moisture Management

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What Is Moisture Management?
The most important role of the building enclosure is to manage the
migration of moisture. Problems associated with moisture are common
and wide-ranging—from mold and rot, to corrosion and degradation, to
leakage and staining—and affect not just the durability, appearance,
and functioning of the building, but the health of the building’s
occupants. Industry data shows that 69% of construction litigation is
associated with moisture-related defects in building envelope
systems.1
No cladding system is 100% impenetrable 100% of the time; it is
impossible to keep all unwanted moisture out of building components.
That is why moisture is “managed,” not “eliminated,” and why “dry
enough” is the objective instead of “dry.” To this end, assemblies must
be designed for water to find a way out when it gets in, and for
components to dry quickly when they get wet.
1Grosskopf, K.R. et al. “Preventing Defect Claims in Hot, Humid Climates.” ASHRAE Journal, July 2008, pp. 40‒52.

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How Does Moisture Move?
A successful building design manages moisture in all its forms: solid, liquid, or gas. Of particular concern to building
designers is water in its most predominant states of liquid and gas.
Liquid water, also called bulk water, includes rain, snowmelt, groundwater, and condensed water vapor. Liquid water
moves via gravity, as well as along the bottom or sides of materials. It also moves from higher pressure to lower pressure,
and by capillary action that draws water up through tube-like spaces or voids. This wicking force acting on wood or wood-
based material is a common source of deterioration.
Water vapor is the gas form of water and is always present in the air. It moves where the air moves, from higher pressure
to lower pressure areas and from hot to cold; air leakage into or out of a building carries moisture with it. The movement of
water vapor with the air is the fastest and largest means of water vapor transport.
Water vapor also moves through materials by diffusion—even when materials appear solid and when nothing appears to
be wet, vapor molecules can move through materials from higher vapor concentrations to lower.

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How Does Moisture Move?
Water changes states from liquid to gas (the process of evaporation) and from gas to liquid (the process of condensation)
depending on factors such as the temperature of the water and the relative humidity of the air. Evaporated water takes the
form of water vapor, which then condenses on a surface as liquid water.
Air moving across a wet surface causes evaporation. An important consideration for selecting building materials is the fact
that once water has entered porous materials via capillary forces, it does not easily evaporate because the molecules are
very tightly bound together. The behavior of water to move from hot to cold is also an important factor in building design.
Water vapor condenses on cooler surfaces (those below the dew point of the surrounding air) and becomes liquid.
Indoor/outdoor pressure differences carry large amounts of moisture through building materials, and when wall cavities
contain the cooler surfaces, moisture accumulation remains hidden from view. The exact point at which this condensation
occurs in the assembly varies seasonally, with accumulation on the interior face of the exterior sheathing in colder
seasons, and on the exterior face of the vapor control layer in warmer seasons.
Those involved in construction and maintenance of the building enclosure must understand how material selection and
installation impacts moisture management in any climate or season. Poor specification, design, and construction have
potentially serious impacts on a building’s durability and performance.

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What Are the Effects of Excessive Moisture?
Mold spores waft through the indoor and
outdoor air continually. When they land on a
damp spot indoors, they may begin growing
and digesting whatever they are on in order to
survive. Mold will not grow if moisture is not
present.
Mold stains and odors are the outward signs of
what is likely a much more severe problem
underneath. Exposure to mold may cause a
variety of health effects: allergy and sinus
problems, asthma, and headaches.
As the EPA states, there is no practical way to
eliminate all mold and mold spores in the indoor
environment; the way to control indoor mold
growth is to control moisture. Images: Environmental Protection Agency

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What Are the Effects of Excessive Moisture?
Moisture has devastating effects on building materials. It can cause rot, swelling, or warping that results in irreversibly
damaged materials, shortening their durability and potentially leading to dangerous structural weaknesses.
The costs of moisture in buildings accrue in multiple ways:
• When a business experiences problems with mold, employee absenteeism and reduced productivity due to illness and
discomfort affect the bottom line.
• Building owners face increased insurance and litigation costs due to damage claims.
• Costs for callbacks and the repair and replacement of building components add up quickly.
• The loss of materials, contents, and the use of space while damage is repaired is a significant expense.
Preventing excess moisture in buildings is accomplished with careful design and construction procedures that address
ventilation, HVAC systems, roofing systems, site drainage, and exterior walls. This course focuses on the last aspect. To
that end, how do the building codes address moisture management in exterior walls?

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Importance of Moisture Management: 2018 IRC
Presented here are the relevant sections of the 2018 International Residential Code. The IRC refers to requirements for
detached one- and two-family dwellings and townhouses not more than three stories above grade.
Chapter 7 Wall Covering
R703.1 General.
Exterior walls shall provide the building with a weather-resistant exterior wall envelope. The exterior wall envelope shall
include flashing as described in Section R703.4.
R703.1.1 Water resistance.
The exterior wall envelope shall be designed and constructed in a manner that prevents the accumulation of water
within the wall assembly by providing a water-resistant barrier behind the exterior veneer as required by Section R703.2
and a means of draining to the exterior water that enters the assembly…

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R703.2 Water-resistive barrier.
One layer of No. 15 asphalt felt, free from holes and breaks, complying with ASTM D226 for Type I felt or other
approved water-resistive barrier shall be applied over studs or sheathing of all exterior walls. Such felt or material shall
be applied horizontally, with the upper layer lapped over the lower layer not less than 2 inches (51mm). Where joints
occur, felt shall be lapped not less than 6 inches (152mm). The felt or other approved material shall be continuous to
the top of walls and terminated at penetrations and building appendages in a manner to meet the requirements of the
exterior wall envelope as described in Section R703.1.
R703.4 Flashing.
Approved corrosion-resistant flashing shall be applied shingle-fashion in a manner to prevent entry of water into the wall
cavity or penetration of water to the building structural framing components. Self-adhered membranes used as flashing
shall comply with AAMA (American Architectural Manufacturers Association) 711. Fluid-applied membranes used as
flashing in exterior walls shall comply with AAMA 714. The flashing shall extend to the surface of the exterior wall finish.
Approved corrosion-resistant flashings shall be installed at:
1. Exterior window and door openings. Flashing at exterior window and door openings shall extend to the surface of the
exterior wall finish or to the water-resistive barrier complying with Section R703.2 for subsequent drainage.
Mechanically attached flexible flashings shall comply with AAMA 712.

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For Exterior Plaster/Stucco:
R703.7.3 Water-resistive barriers.
Water-resistive barriers shall be installed as required in Section R703.2 and, where applied over wood-based
sheathing, shall include a water-resistive vapor-permeable barrier with a performance at least equivalent to two layers
of Grade D paper. The individual layers shall be installed independently such that each layer provides a separate
continuous plane and any flashing (installed in accordance with Section R703.4) intended to drain to the water-resistive
barrier is directed between the layers.
Exception: Where the water-resistive barrier that is applied over wood-based sheathing has a water resistance equal to
or greater than that of 60-minute Grade D paper and is separated from the stucco by an intervening, substantially non-
water-absorbing layer or designed drainage space.
States vary in which year of the IRC they have adopted. In addition, many states or local authorities amend the code with
specific revisions. For example, Oregon requires a minimum ⅛″ space between the water-resistive barrier and the exterior
veneer (with exceptions addressing remodeling, tested assemblies, pan flashings, and weather-resistive barriers with
enhanced drainage). It’s important to keep in mind that final code decisions rest with the local authority having jurisdiction.

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Importance of Moisture Management: 2018 IBC
Similar language is found in the 2018 International Building Code:
Chapter 14 Exterior Walls
1402.2 Weather protection.
Exterior walls shall provide the building with a weather-resistant exterior wall envelope. The exterior wall envelope shall
include flashing, as described in Section 1404.4. The exterior wall envelope shall be designed and constructed in such
a manner as to prevent the accumulation of water within the wall assembly by providing a water-resistive barrier behind
the exterior veneer, as described in Section 1403.2, and a means for draining water that enters the assembly to the
exterior. Protection against condensation in the exterior wall assembly shall be provided in accordance with Section
1404.3.
1403.2 Water-resistive barrier.
Not fewer than one layer of No. 15 asphalt felt, complying with ASTM D226 for Type I felt or other approved materials,
shall be attached to the studs or sheathing, with flashing as described in Section 1404.4, in such a manner as to
provide a continuous water-resistive barrier behind the exterior wall veneer.

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Importance of Moisture Management: 2018 IBC
1404.4 Flashing.
Flashing shall be installed in such a manner so as to prevent moisture from entering the wall or to redirect that moisture
to the exterior. Flashing shall be installed at the perimeters of exterior door and window assemblies, penetrations and
terminations of exterior wall assemblies, exterior wall intersections with roofs, chimneys, porches…
For Cement Plaster/Stucco:
2510.6 Water-resistive barriers.
Water-resistive barriers shall be installed as required in Section 1403.2 and, where applied over wood-based sheathing,
shall include a water-resistive vapor-permeable barrier with a performance at least equivalent to two layers of water-
resistive barrier complying with ASTM E2556, Type I. The individual layers shall be installed independently such that
each layer provides a separate continuous plane and any flashing (installed in accordance with Section 1404.4)
intended to drain to the water-resistive barrier is directed between the layers.
Exception: Where the water-resistive barrier that is applied over wood-based sheathing has a water resistance equal to
or greater than that of a water-resistive barrier complying with ASTM E2556, Type II and is separated from the stucco
by an intervening, substantially non-water-absorbing layer or drainage space.

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Moisture Management Strategies
Moisture management strategies typically follow what is often referred to as the four Ds:
• Deflection: Minimize the moisture exposure of materials by deflecting water away from them.
• Drainage: Develop paths to drain away any moisture that does penetrate the assembly.
• Drying: Ensure means of ventilation and evaporation to remove residual moisture.
• Durability: Select materials that can withstand exposure to periodic wetting without compromising their performance.
Different materials vary in their tolerances for both amount of moisture and length of time they can be wet.
Because it is practically impossible to eliminate moisture sources, paths, and movement forces, the choice of material,
arrangement, and proper installation and detailing is paramount.

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Moisture Management Strategies
The exterior wall type addressed in this course is composed of the:
• exterior cladding, which manages rainwater intrusion and is the first
line of defense against bulk water penetration
• continuous drainage plane, drainage space, flashings, and weep
holes; the drainage plane is at the line between wet and dry zones
and includes heat, air, and moisture control layers
• insulating elements (inboard or outboard of the drainage plane layer
depending on the region and climate), which regulate heat loss and
gain, and
• structural elements, which control dead and live loads.
We’ll now investigate the materials that form the components of the
continuous drainage plane: water-resistive barriers (WRBs) that also
offer air and vapor barrier capabilities, flexible flashings, sealants, and
primers.
WRB

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Review
Question
Why is building moisture
management best summed
up as a four Ds strategy?

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Answer
Because it’s impossible to
keep all unwanted moisture
out of building components,
the four Ds present the best
methods of managing it.
Deflect water away from materials.
Drain any moisture that
penetrates.
Dry residual moisture through
ventilation and evaporation.
Durable materials that can
withstand exposure to periodic
wetting should be specified.

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Moisture Management Materials for Exterior Walls

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Water-Resistive Barriers
Water-resistive barriers, WRBs, form a drainage plane on a
building’s exterior wall, repelling and shedding water from the back
side of the drainage space behind the cladding. The use of WRBs
in a wall system recognizes that some amount of water will pass
through the surface of the building envelope; WRBs provide a
redundancy in the assembly. WRBs may be designed to also act
as an air and/or vapor barrier.
A WRB should perform for the life of the building, so it must be
strong enough to handle installation, and compatible with and able
to integrate with adjacent materials. Advanced performance WRBs
may also provide a means of directing water out of the wall cavity
and may offer surfactant and extended UV resistance.

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WRB Types: Asphalt-Saturated Felt
Asphalt-saturated felt approved for walls in the building codes is that which
meets ASTM D226, “Standard Specification for Asphalt-Saturated Organic Felt
Used in Roofing and Waterproofing.” Type I is commonly called No. 15, and
Type II is commonly called No. 30.
Felt consists of multiple layers of loosely laid cellulose fibers. The fiber source is
unbleached softwood pulp and contains a high percentage of recycled fibers.
The felt’s short fiber length makes it brittle; it requires greater thickness than
other materials to achieve the necessary strength.

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WRB Types: Asphalt-Saturated Kraft Paper
Asphalt-saturated kraft, or building, paper is composed of a
single layer of cellulose fibers. The fiber source is mostly
virgin, unbleached softwood pulp and may include a small
percentage of recycled fiber. Longer fibers allow asphalt-
saturated kraft paper to be thinner and less brittle than felt, so
it is less likely to tear during installation around corners and in
tight conditions. It typically comes in rolls that allow easy
storage and installation.
Options include single-ply Grade D, meeting the minimum
water resistance time of 10 minutes as required by the
building codes, as well as papers that pass 20-, 30-, and
more than 60-minute tests. Also available are two-ply options,
so that when two layers are required, only one installation
pass is needed. Dual layers result in better sealing around
fasteners and better building envelope integration. Some
manufacturers offer such two-ply products with 150 minutes
of water resistance.

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WRB Types: Woven Polymeric
Woven polymeric housewraps are one type of mechanically attached WRB.
These economical products are made of plastic tapes woven in two
directions and coated with a waterproofing film. Woven WRBs protect against
water intrusion and air infiltration from the outside and are usually micro-
perforated to allow moisture vapor to pass through the film from the inside.
A cross-woven polypropylene fabric provides solid tensile strength and can
be combined with a UV-resistant polyolefin coating that provides up to 120
days of exposure time. Some manufacturers offer a semitransluscent product
that installs quickly since the studs are easy to locate through the
housewrap.

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WRB Types: Nonwoven Polymeric
Another type of mechanically attached WRB is a nonwoven, nonperforated
polymeric material that includes spunbonded fabric-like polymers and coated film
products. The appearance of the spunbonded material is dependent on the heat-
pressing or embossing of the fabric. The formulations are typically trade secrets
and may include many kinds of polymer resins.
The upper, yellow photo shows the noncoated side of a spunbonded fabric WRB.
The black and white picture shows a heat-pressed spunbonded WRB. The fibers
on both faces melt together and flatten while the fibers in the center remain similar
to the yellow picture. The webs in the fabric prevent liquid water from passing
through the fabric.
Some nonwoven polymeric WRBs offer surfactant resistance to chemicals
encountered on the job site or used by homeowners in the form of power washing
solutions and detergents.

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WRB Types: Drainable
Drainable WRBs direct moisture down to the
ground. The near right example is of a woven
material with directional fibers; the far right
shows a WRB with integrated filament.
Embossed
bumps
Embossed products are made by heat-pressing spunbonded polymeric fabric over rollers to
produce a pattern. The raised bumps provide a separation from adjacent materials and channel
moisture away from the wall assembly to the ground. The nonperforated breathable barrier
layer is durable and UV stable, and resists tears, abrasions, and punctures.

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WRB Types: Two-Ply Hybrid
A two-ply hybrid system provides a
built-in drainage space between the
layers. Asphalt-saturated Grade D
kraft sheathing paper is backed by a
nonwoven, spunbonded polymeric
layer. This nonperforated breathable
barrier channels water away from
the wall assembly, providing an
extra layer of protection and
durability in one installation.
This drainable solution saves the
considerable labor of wrapping the
building twice and adds the benefits
of a single source and warranty.

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Self-adhesive WRBs typically come in rolls and consist of an adhesive polymeric sheet
on a release paper. They are available as permeable (allowed for wood-based
construction) and nonpermeable. A self-adhesive WRB is typically self-sealing and
performs as an air barrier that can improve the energy efficiency of a structure.
Liquid-applied WRBs are offered in both permeable and impermeable formulations and
may provide some degree of nail sealability. Issues include expansion and contraction
and building movement, and they are more expensive than other methods.
Composite WRBs consist of OSB or an insulating board and a laminated WRB. These
systems must rely on taped seams to prevent water intrusion; if not taped perfectly,
water is directed between the panel seams because there is no lapping of the WRB.
WRB Types: Self-Adhesive, Liquid-Applied, and Composite
Self-adhesive WRB
Composite WRB

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WRB Applicable Testing and Standards
Depending on the type and features of WRB selected, there are several applicable standards and test methods:
• ASTM D779: Standard Test Method for Water Resistance of Paper, Paperboard, and Other Sheet Materials by the Dry
Indicator Method
• ASTM D5034: Standard Test Method for Breaking Strength and Elongation of Textile Fabrics (Grab Test)
• ASTM E96: Standard Test Method for Water Vapor Transmission of Materials
• ASTM D882: Standard Test Method for Tensile Properties of Thin Plastic Sheeting
• ASTM D828: Tensile Properties of Paper and Paperboard Using Constant-Rate-of-Elongation Apparatus
• ASTM D4533: 11 Standard Test Method for Trapezoid Tearing Strength of Geotextiles
• AATCC-127 (American Association of Textile Chemists and Colorists) Method 127 Water Resistance: Hydrostatic
Pressure Test
• ASTM E 2556: Standard Specification for Vapor Permeable Flexible Sheet Water-Resistive Barriers Intended for
Mechanical Attachment

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WRB Additional Testing
Some products are tested for additional performance qualities:
Air permeance testing is used when designing an air barrier assembly on the building, which includes not only walls, but
also the floor and roof.
• ASTM E1677: Standard Specification for an Air Barrier Material or System for Low-Rise Framed Building Walls
• ASTM E2178: Standard Test Method for Air Permeance of Building Materials
• ASTM E2357: Standard Test Method for Determining Air Leakage of Air Barrier Assemblies
Fire Testing:
• ASTM E84: Standard Test Method for Surface Burning Characteristics of Building Materials
• Class A flame spread standard 0‒25; smoke development standard 0‒450
• NFPA 285: Standard Fire Test Method for Evaluation of Fire Propagation Characteristics of Exterior Wall Assemblies
Containing Combustible Components
Drainage Efficiency
• ASTM E2273: Standard Test Method for Determining the Drainage Efficiency of Exterior Insulation and Finish Systems
(EIFS) Clad Wall Assemblies

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Flashings
WRBs must be interconnected with flashings to manage
moisture effectively. Flashings are integral to moisture
management because transitions between materials and
components exist in almost all buildings; flashings serve to
bridge these transitions to prevent weak points where
moisture may cause damage. The image here shows
locations where flashings are necessary for a window
installation.
Again, the idea is not to absolutely prevent water from
entering, but to convey it away before it results in
deterioration.
Flashings must be compatible with the products they come in
contact with. The sequencing of the flashing is critical for
proper deflection.

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Flashing Types: Self-Adhesive
SBS Modified Asphalt Self-Adhesive Flashing
The elastomeric compound styrene-butadiene-styrene (SBS) is added to asphalt. Physical
properties such as adhesion at low temperatures, the upper softening point, and general
adhesion can be modified by adjusting the percentage of SBS and the adhesive formulation.
Some materials are not compatible with asphalt flashing.
Butyl Self-Adhesive Flashing
Butyl rubber is a synthetic rubber compound. This type is typically offered at a higher price
than SBS asphalt but usually has better chemical compatibility with other materials. It offers a
broader range of application temperatures and a higher service temperature range.
Asphalt Butyl Blend Self-Adhesive Flashing
Butyl rubber is blended or placed in alternating layers with SBS modified asphalt. Usually
priced between SBS asphalt and butyl flashing, this blend may increase adhesion or other
performance characteristics, but compatibility with other materials still needs to be verified.

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Flashing Types: Self-Adhesive
Acrylic Self-Adhesive Flashing
This flashing provides resistance to many solvents, UV light, elevated
temperatures, and plasticizers. It generally has a low to moderate
initial tack and adhesion; it does not adhere well to low-surface energy
substrates such as polyethylene and polypropylene—common
materials for WRBs.
Foil-Faced Self-Adhesive Flashing
Foil-faced flashing comes with great variety in the type of adhesive
and has a high UV resistance.
Advances in Adhesives
New adhesive formulations like block copolymers broaden the
application temperature range (in some cases as low as 0º F) and
provide aggressive adhesion.
Asphalt Butyl Blend
Foil-Faced

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Primer
When installing self-adhesive flashing, good adhesion is essential. Substrate materials, surface contamination, and low-
temperature conditions can all interfere with proper adhesion. A primer is sometimes needed to help the self-adhesive
flashing material bond to the substrate, improving adhesion by filling gaps and adding a tacky surface.
A polymer emulsion-based primer works with masonry, concrete, non-treated wood, drywall, metal, and fiberglass mat
gypsum board, and is easily applied by brush, roller, or spray equipment. Once applied, it sets to a tacky film that provides
increased adhesion. Look for a water-based, low-VOC formulation that is nonflammable while wet and contains no harsh
solvents.

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Flashing Types: Mechanically Attached
Mechanically attached flashing does not have an adhesive backing but instead is affixed with fasteners installed behind
where the window mounting flange and sealant will cover the fasteners. A line of sealant at the head is required to seal the
flashing to the substrate.

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Flashing Types: Flexible and Liquid-Applied
A flexible, self-adhering waterproof flashing is applied on
curved or arched window or door openings, and molded
for one-piece sill pans and around penetrations. It is
made of a butyl compound and a cross-laminated
polymeric film that features exceptional stretch and
durability in one or two directions. It is ideal for plywood,
OSB, aluminum, and wood and vinyl windows.
Liquid-applied flashing is a relatively new product that is
painted on or trowel-applied. The membrane coating can be
used in conjunction with other flashings and is particularly
useful for recessed openings, round penetrations, or other
types of complicated openings. Experience is necessary to
achieve proper application.

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Flashing Types: Specialty
Specialty flashing is used around difficult areas such as
electrical boxes, window corners, and pipes and is
easily integrated with the WRB and other flashing
products.
A pre-sized polymeric membrane boot is used for
flashing pipe penetrations and comes in a wide range
of sizes (lower left and center photos).

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Sealants
Sealants must be compatible with all the different components that
work together. Applied with an ordinary caulking gun, a continuous
bead of sealant on the window nail flange gives long-lasting
protection against moisture infiltration. Some sealants can also
take paint in visible application areas.
Applicable standards:
ASTM C920: Standard Specification for Elastomeric Joint
Sealants
• Type S, Grade NS, Class 25, Use NT, Use A, Use M, Use
G, Use O
AAMA 808.3 Exterior Perimeter Sealing Compound

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Flashing Applicable Testing and Standards
Compatibility is critical among sealants, primers, and flashing and other adhesives. When sealants are used with self-
adhered flashing and not tested for compatibility, there is opportunity for catastrophic waterproofing failures.
• AAMA 711: Voluntary Specification for Self Adhering Flashing Used for Installation of Exterior Wall Fenestration Products
• AAMA 712: Voluntary Specification for Mechanically Attached Flexible Flashing
• AAMA 713: Voluntary Test Method to Determine Chemical Compatibility of Sealants and Self-Adhered Flexible Flashings
• AAMA 714: Voluntary Specification for Liquid Applied Flashing Used to Create a Water-Resistive Seal around Exterior Wall
Openings in Buildings
• ASTM D779: Standard Test Method for Water Resistance of Paper, Paperboard and Other Sheet Materials by the Dry Indicator
Test Method
• AATCC Test Method 127: Water Resistance: Hydrostatic Pressure Test
• ASTM D882: Standard Test Method for Tensile Properties of Thin Plastic Sheeting
• ASTM D5034: Standard Test Method for Breaking Strength and Elongation of Textile Fabrics (Grab Test)
• ASTM D1970: Standard Specification for Self-Adhering Polymer Modified Bituminous Sheet Materials Used as Steep Roofing
Underlayment for Ice Dam Protection
• ASTM E311: Standard Test Method for Water Penetration of Exterior Windows, Skylights, Doors, and Curtain Walls by Uniform
Static Air Pressure Difference
• ASTM E96: Standard Test Methods for Water Vapor Transmission of Materials

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ICC Acceptance Criteria
ICC Acceptance Criteria define the testing
methods and performance requirements for
materials to be accepted in the building code.
• ICC AC-38 for Water-Resistive Barriers
• ICC AC-148 for Flashing Materials
• ICC AC-356 Drainage Systems for Plaster or
Masonry Veneer
Replace with “Raleigh WSmart4-07 008”

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Review
Question
What is the difference
between these two woven
WRBs?

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Answer
Both WRBs are mechanically
attached polymeric material.
The green WRB includes
directional fibers that drain
moisture by sending it down
to the ground.

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Installation Guidance and Methods

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Choosing the Right Materials
The success of a moisture management system depends on all of the components in the building envelope performing
equally well. It is essential to use products that are compatible. Selection is simplified by using a single-source
manufacturer of WRBs, flashings, sealants, and tapes that have all been tested and rated as individual components and
verified to work together as a system.
Service temperature is another important consideration. The exterior of wall assemblies can become quite hot—especially
under dark-colored cladding, in hot regions, or with a western/southern exposure. Be sure to choose material suitable for
the expected service temperatures.
The appropriate flashing is determined by factors such as budget, local practices, or job site sequencing.

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Choosing the Right Materials
Material choice is also based on cladding type. Polymeric WRBs are appropriate for fiber cement siding, wood, and vinyl.
Stucco, masonry, and brick generally require two layers of WRB, with the most outward layer being Grade D paper.
Drainable WRBs are an excellent choice for locations with wetter conditions, or where high performance is desirable. Be
sure the drainage channels do not compress during installation or they will be rendered ineffective.
Warranties are about more than just length of time—be sure to check the details. Many warranties apply only if a complete
system from a single manufacturer is used, or are valid only to the initial purchaser.

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Installation Guidance
The WRB can be installed before the windows or after. Install the WRB starting from the bottom of the wall—consider that
a drop of water running downward will enter gaps that result if lower levels overlap higher levels. Lap each course over the
top of the lower course in shingle fashion.
Because wind pressure can drive water sideways or upwards, a sufficient overlap must be installed.
• 6″ minimum vertical overlap
• 2″ minimum horizontal overlap (3″ recommended)

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Accessories
Sealants, tapes, backer rods, transition membranes,
primers, and fasteners can all be used to fasten
WRBs to the structure of the building and/or to
maintain air tightness between air barrier
components and assemblies.
Sheathing tape prevents water intrusion at seams
and helps reduce damage from winds getting behind
the WRB at lapped seams. Sheathing tape is
required for an air barrier installation.
Specialty products are available for sealing around
various through-wall penetrations, boxes, and vents.
Liquid flashing can seal the penetration to the WRB.
Special detailing is required when using drainable
wraps and rainscreens.

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Fasteners and Furring Strips
Fasteners such as cap staples, cap nails, or
roofing nails must be exterior grade and
corrosion resistant. They should be spaced
as needed to secure the WRB until the
exterior cladding is installed. Distance
between fasteners is specified by the
manufacturer or the codes.
Another method of securing the WRB to the
exterior sheathing is with continuous furring
strips installed vertically along stud lines. Use
the minimum number of fasteners to hold the
WRB in place until furring strips are applied.
Furring strips provide an air gap between the
siding and the WRB that contributes to
improved drainage.
Fasteners Furring Strips

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WRB Installation Example
Presented here is a general WRB
installation example; always follow
manufacturer instructions. Compliance
with the building code and proper
installation are critical in reducing
potential water intrusion. It is the
responsibility of the architect or builder
to ensure that these standards are met.
Install housewrap over an approved
exterior sheathing (1). Starting at the
bottom of one end of the wall, place the
housewrap roll horizontally and roll out
the first course evenly, covering rough
window and door openings. When
starting at a corner, overlap by a
minimum of 12″.
1)

< >
WRB Installation Example
Fasten the membrane securely to the exterior wall with
appropriate fasteners (2). It is recommended to use 1″
plastic caps or 1″ crowned staples that penetrate the
studs to attach housewrap so that it is taut and flat. The
proper spacing for these fasteners is 24″ on center,
maximum. Closer spacing may be required based on
site conditions.
At vertical seams, apply a minimum of 6″ vertical
overlap (3). When going around corners, make sure
housewrap is pulled tightly and properly fastened. Any
succeeding course should be placed horizontally over
the lower course in a weatherboard fashion with a
minimum horizontal overlap of 6″. It is recommended to
tape all vertical seams with sheathing tape. All seams
must be taped to achieve an air barrier installation.
2) Fastening
3) Overlap and Tape Seam

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Flashing Width
AAMA offers minimum self-adhesive flashing width criteria.
• Flashing width shall extend at least 2″ (50mm) past the critical interface
of the window flange or frame and sheathing.
• The critical interface includes but is not limited to the window/door
flange and sheathing interface, nails or penetrations through the
window/door trim, and trim and the siding/cladding interface.
• Flashing should be a minimum of 4″ wide.
Following are flashing installation examples for AAMA methods B and A1 as
well as corner protection guidance. These are presented for illustrative
purposes only; always follow manufacturer instructions. Compliance with
the building code and proper installation are critical in reducing potential
water leakage points.

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AAMA Method B Self-Adhesive
or Mechanically Attached Flashing Installation
Method B is designed for integral flanged
window applications where the window is
installed before the WRB is applied.

< >
Cut the sill flashing
the width of the rough
opening plus two
times the width of the
flashing. Attach the
flashing along the
bottom of the rough
opening. Be sure not
to fasten the lower
edge of the flashing
so that a WRB may
be slipped underneath
in a weatherboard
fashion (1a).
1) Sill Flashing 2) Jamb Flashing
Cut the jamb flashing to the rough opening height plus two times the width of the flashing, minus 1″. Align the flashing
flush to the edge of the rough opening and even with the bottom of the sill flashing. Attach the jamb flashing at the rough
opening (2a). As with the sill flashing, do not fasten the lower edge of the jamb flashing (2b). Repeat for the remaining
jamb.

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To ensure adhesion, wipe the window flange, sill, and jamb flashing with a clean rag (a). Before installing the window,
apply a continuous ⅜″ bead of sealant to the back side (interior) of the mounting flange near the outer edge (b). The
3) Window Installation
sealant may also be
directly applied to the
perimeter of the rough
opening as long as a
continuous seal is
ensured (c). Then install
the window according to
the manufacturer’s
instructions.

< >
The length of the head flashing is the width of the rough
opening plus two times the width of the flashing plus 2″. To
install the head flashing, apply a continuous ⅜″ bead of sealant
on the top (head) mounting flange (a).
Embed the head flashing over the sealant; press the head
flashing until the sealant appears at the bottom edge. When
using a self-adhesive flashing, sealant at the head flange is not
necessary. Be sure to extend the flashing beyond each jamb
flashing. Fasten in place.
4) Head Flashing

< >
Integrate the first course of building paper under the sill flashing to provide for proper drainage of water. Shingle the
second course of building paper over the layer below, jamb flashing, and head flashing. The last course is shingled over
the second.

< >
AAMA Method A1 Self-Adhesive Flashing Installation
Method A1 is designed for integral flanged window
applications where the window is installed after the WRB
is applied.

< >
Make diagonal cuts to the WRB at the top of the rough opening
corners. For 9″ flashing, measure as follows: 9″ up and 9″ over,
making a 45° angle (1a). Cut on the diagonal from the marked
point to the rough opening corner. Gently raise the top edge of
the WRB and tape the corners and center to the barrier surface
above. This will allow for the installation of the window and the
jamb and head flashing later.
Cut the sill flashing to the width of the rough opening plus
twice the flashing width. Wipe the surface of the WRB with a
clean rag to ensure proper adhesion. Remove the release
paper and press the sill flashing in place so that the edge of the
flashing’s adhesive is level with the top edge of the rough
opening (2).
1) Modify WRB
2) Sill
Flashing

< >
Before installing the
window, apply a
continuous ⅜″ bead of
sealant to the back side
(interior) of the
mounting flange (3).
Install the window
according to the
manufacturer’s
instructions.
3) Window Installation 4) Jamb Flashing
Prior to installing the jamb flashing, wipe the jamb flange and WRB with
a clean rag. Then cut two strips of flashing long enough to extend
beyond the sill flashing and 2″ below the top of the head flashing (4a).
Remove the release paper and align the flashing flush against the
window frame with the adhesive strip covering the entire window flange.
Follow this procedure for the other side of the window.

< >
Wipe the head flange, jamb flashing, WRB, and sheathing with a
clean rag. Cut a piece of head flashing long enough to ensure that it
extends a minimum 1″ beyond the jamb flashing (5a). Install the head
flashing by pressing firmly in place in one direction to prevent voids.
Finally, allow the flap of the WRB at the head to lie flat over the head
flashing. Apply a new piece of sheathing tape over the entire diagonal
cut made in the WRB and press firmly in place (5b).
5) Head Flashing

< >
Corner Protection Option
The corner protection option can be used with any AAMA window installation method.
1. Apply beveled siding into the sill to provide a positive slope to the outside of the building.
2. Apply a 9″ wide perimeter sill flashing.
3. Apply two preformed corner boots.
4. Wrap a second layer of self-adhesive flashing onto the sill and overlap a minimum of 3″ over the perimeter sill flashing.
5. Apply a ⅜″ sealant bead around the window flange, leaving two 2″ gaps at the sill for drainage out the front.
6. Continue with the remainder of the installation. Provide a back dam and air seal to the interior of the rough framing.
1 2 3 4 5 6

< >
Review
Question
What is wrong with this image
of WRB installation?

< >
Answer
Each course must be lapped
over the top of the lower
course in shingle fashion to
prevent water from entering
the gaps as it runs downward.

< >
Epic Fails

< >
Mold and Rot
Here, the improper kick-out of the flashing
from the roof directed water onto the wall,
ultimately causing mold and rot.

< >
Mold and Rot
Through-wall penetrations, particularly windows and doors, are most
vulnerable to weatherization errors. Here, missing flashing allowed water into
the wall, resulting in significant damage.

< >
Structural Weakening
A drainage path was not
designed into this system to get
the water off the beam. Water
was thus allowed to collect on
the bottom and rot the wood.

< >
Weatherproofing Failure
Incompatible products can react chemically and fail to
weatherproof.
When sealant is used with flashing, a compatibility test
should always be done. Chemical reactions between
sealants and flashings can be disastrous and result in
costly litigation. Most manufacturers offer systems
formulated to work together.

< >
Weatherproofing Failure
Incompatible products can
react chemically and result
in unsightly leaking. This
again is an example of
chemical incompatibility that
could have been prevented
with proper testing.

< >
Improper Use of Material
This example shows housewrap used as the jamb
flashing. Housewrap does not meet the same
standards as flashing and is not designed for this
use.

< >
Summary and Resources

< >
Summary
Industry data shows that 69% of construction litigation is moisture-related.
Moisture is everywhere, and it is no simple feat to successfully manage it in buildings. The many concerns that must be
addressed—from the various forms of water, to the many sources, paths, and mechanisms for moisture to enter an
enclosure, to the interactions, moisture storage, and drying behaviors of different materials—all add to the complexity of
managing moisture. Further challenges come in keeping construction costs and installation techniques within achievable
boundaries.
Remember that no single exterior wall component can effectively manage moisture on its own; the complete exterior
assembly—WRB, flashings, windows, doors, and sealants—must function together as a system. Specification of moisture
management components is simplified by using a single-source manufacturer who offers materials that have been tested
and verified to work together as a system.

< >
Resources
2018 International Building Code®. International Code Council, 2017.
2018 International Residential Code®. International Code Council, 2017.
Dorin, Leonard. “The Importance of Integrating Flashing and the Water Resistive Barrier in the Exterior Wall Systems of
Residential Buildings.” Journal of ASTM International, vol. 3, no. 5, 2006, pp. 1‒6.
Environmental Protection Agency. “Moisture Control Guidance for Building Design, Construction and Maintenance.” EPA,
2013, https://www.epa.gov/sites/production/files/2014-08/documents/moisture-control.pdf. Accessed July 2019.
Environmental Protection Agency. “Mold.” EPA. EPA, 2016, https://www.epa.gov/mold. Accessed July 2019.
Grosskopf, K.R. et al. “Preventing Defect Claims in Hot, Humid Climates.” ASHRAE Journal, July 2008, pp. 40‒52.
Kesik, Ted J., Ph.D. “Moisture Management Concepts.” Whole Building Design Guide. National Institute of Building
Sciences, 2014, https://www.wbdg.org/resources/moisturemanagementconcepts.php. Accessed July 2019.
Kesik, Ted J., Ph.D. “Moisture Management Strategies.” Whole Building Design Guide. National Institute of Building
Sciences, 2014, https://www.wbdg.org/resources/moisturemanagementstrategies.php. Accessed July 2019.
Lemieux, Daniel J. “Building Envelope Design Guide—Wall Systems.” Whole Building Design Guide. National Institute of
Building Sciences, 2010, https://www.wbdg.org/design/env_wall.php. Accessed July 2019.

< >
Conclusion
©2016, 2019 Henry Company. The material contained in this course was
researched, assembled, and produced by Henry and remains its property.
Questions or concerns about the content of this course should be directed to the
program instructor. This multimedia product is the copyright of AEC Daily.
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