This Online Learning Seminar is available
through a professional courtesy provided
by:
Moisture Management
In
Sidewall Construction
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Benjamin Obdyke
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this course
199 Precision Drive
Horsham, PA 19044
Telephone:215-672-7200
Fax:215-672-3731
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E-mail: [email protected]
Internet: http://www.benjaminobdyke.com
©2004 Benjamin Obdyke. The material contained in this course was researched, assembled, and
produced by Benjamin Obdyke and remains their property. Questions or concerns about this course
should be directed to the instructor.
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Slide 1 of 51
• About the Instructor
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Moisture Management in Construction
MOISTURE MANAGEMENT IN SIDEWALL CONSTRUCTION
Presented By:
George Caruso
Benjamin Obdyke Incorporated
199 Precision Drive
Horsham, PA 19044
Description:
Pressure-equalized rainscreen wall system design for light
frame construction
AIA/CES Info:
Provider No. J624 – Course No. AEC003; LUs - 1
MCE Info:
Contact your respective governmental licensing &
regulatory agency.
Expiration date:
Jan 31, 2006
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Slide 2 of 51
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Moisture Management in Construction
HOW TO USE THIS ONLINE LEARNING COURSE
•
Read and review the material contained in this seminar.
•
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To view this presentation, use the previous/next keys on each slide or the up and
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To receive a certificate indicating course completion, refer to the instructions at the
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For additional information and post-seminar assistance, click on any of the logos and
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Slide 3 of 51
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Moisture Management in Construction
PROTECTING WALL SYSTEMS
FROM DAMAGING EFFECTS OF MOISTURE
Wind driven rain from the outside, moisture vapor from the home’s interior, and
corrosive surfactants that leak from certain types of siding usually remain trapped
in between the siding and building paper or housewrap.
Left alone, this unvented moisture can negatively impact the performance of the
wall assembly, including sheathing, housewrap, building paper and exterior cladding
systems. It can also lead to the development of mold and mildew, a potential health
concern which often remains hidden in the wall space. More noticeably, trapped
moisture can cause paints and stains to peel or blister prematurely. A vented,
continuous rainscreen barrier helps solve the moisture problem and prevent
its negative consequences by effectively draining and venting moisture from
behind the siding.
A new industry technology utilizing Void Space Technology, a unique three
dimensional plastic matrix provides a continuous space for drying, channels for drainage,
a thermal break, and pressure equalization, allowing moisture to escape quickly before
it damages the sidewall materials. Wood, fiber-cement, stucco, stone veneer, and EIFS
systems, as well as brick and vinyl, are ideal cladding systems for use with this type of
rainscreen system.
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Slide 4 of 51
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Moisture Management in Construction
AN INDUSTRY PERSPECTIVE
“The fundamental function of the building envelope is its separation of the outside
and the inside environments so that indoor conditions can be controlled to meet
many requirements (for example, comfort and energy efficiency). The design and
construction of durable, efficient walls requires consideration of climate loads to
which these building components will be exposed. A wall assembly that is trouble-free
in one area of the country may not perform adequately in another. This is because
although the building physics do not change, the heat, air and moisture
(liquid and vapor) control strategies may need to integrate different levels of
redundancy for different climate conditions. The severity of the climate for a building
site cannot be changed, but it needs to be integrated in the design of the wall
assemblies. Understanding the climate loads acting on building components is an
important step towards effective design of moisture management strategies.”(1)
(1) Cornick, S. and Rousseau, M.Z., “Understanding the Severity of Climate Loads for Moisture-related
Design of Walls”, IRC Building Science Insight 2003 Seminar Series, Toronto, CA, Oct. 2003, pp.1
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Slide 5 of 51
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Moisture Management in Construction
LEARNING OBJECTIVES
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Recognize how moisture infiltrates the building skin through side
wall conditions.
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Understand the implications of water infiltration into the building.
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Determine appropriate ways to employ rainscreen principles for a
variety of cladding systems.
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Slide 6 of 51
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Moisture Management in Construction
HOW DOES MOISTURE INFILTRATE THE BUILDING
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Driving Rain / Strong Winds
– Wind driven rain from the exterior can be forced into small openings in the
cladding materials at joints, laps, nail holes, etc.
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Slide 7 of 51
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Moisture Management in Construction
MOISTURE INTRUSION
•
Moisture is involved in most premature deterioration and mold
problems in the building envelope of a home. Precipitation,
vapor drive from within the building, ambient humidity and
moisture released from many materials within the new home
provide for a constant source of moisture.
•
Joints and junctions, permeable building materials, and
imperfect application details often provide entry paths for the
moisture to travel. Since walls today are not built to dry,
accumulation of moisture can lead to numerous problems.
•
A moisture management strategy employing a vented,
continuous rainscreen, and a drainage plane, such as
housewrap or building paper, can properly drain liquid water
out of the wall assembly.
•
Openings at the top and bottom of the cavity allow for a
convective ventilation path for outside air.
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Slide 8 of 51
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Moisture Management in Construction
MOLD
•
Mold is a type of fungus and is fast becoming one of the most contentious issues in
the home building industry. The dark, damp, and unventilated regions of a wall
assembly provide a capable habitat for mold to thrive. Mold can grow on wood and
any cellulose-based material, and even on the dirt present on inorganic materials
such as concrete, metal, and fiberglass insulation.
•
People are mainly exposed to mold by breathing in spores. The most common
health problems caused by indoor mold are allergy symptoms. More hazardous
“toxic molds” include stachybotrys, cladosporium, chaetomium, and aspergillus.
Molds also secrete digestive fluids that decompose wood. Mold can even digest
some synthetic materials such as adhesives and paints.
•
A mold problem is a moisture problem and the way to control mold growth is to
control moisture. A vented continuous rainscreen barrier helps to reduce trapped
moisture in a wall assembly by providing channels for ventilation and drainage of
moisture behind cladding. This moisture management strategy can help to reduce
mold growth.
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Slide 9 of 51
• About the Sponsor
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Moisture Management in Construction
HOW DOES MOISTURE INFILTRATE THE BUILDING
•
High Humidity / Extreme Temperatures
– Moisture vapor (“vapor- drive”) from the interior can pass through the shear
wall condensing on the cold, outer surface.
– Positive pressure is created by air conditioned space.
www.bia.org
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Slide 10 of 51
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Moisture Management in Construction
WIND & RAIN ACTING TOGETHER CAUSE WATER INFILTRATION
•
Wind can blow the rain sometimes horizontally into cracks and holes in the
exterior walls.
•
Wind blowing around the building can create a negative pressure within the wall.
.
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Slide 11 of 51
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Moisture Management in Construction
WIND & RAIN ACTING TOGETHER CAUSE WATER
INFILTRATION
•
With the driving rain on the exterior and
the negative pressure within the wall, water
gets pulled into the cavity.
•
Standing water can wick up into the wall
cavity if the sill conditions are not properly
finished, this can happen at the bottom of
walls but also around window and door
openings.
•
Extreme temperature swings can cause
fatigue on the building skin, creating cracks
and pockets that allow for water
infiltration.
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Slide 12 of 51
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Moisture Management in Construction
WHAT ARE THE RESULTS OF MOISTURE INFILTRATION
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Exterior Surfaces Deteriorate
– Paint and stucco/EIFS will crack and peel,
unless damaged substrate is repaired
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Slide 13 of 51
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Moisture Management in Construction
WHAT ARE THE RESULTS OF MOISTURE INFILTRATION
•
Mold – Mildew – Rot
– Mold and Mildew spores exist in the
environment.
– Wet wood and gypsum products
create a food source for the mold
and mildew to grow.
– As mold and mildew grow they
cause the wall system to rot.
– Interior mold and mildew create a
condition called “sick building
syndrome” that can be a health
hazard to people with allergies.
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Slide 14 of 51
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Moisture Management in Construction
WHAT ARE THE RESULTS OF MOISTURE INFILTRATION
•
Structural Damage
– Water can also undermine the structural integrity of a building, causing an
unsafe environment to work and live in.
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Moisture Management in Construction
MOISTURE MANAGEMENT METHODS
•
Deflection
– Use architectural elements to keep water
from entering wall system.
•
Drainage
– Rainscreen type assemblies used to remove
water from system.
•
Drying
– Wall assembly allows water to evaporate
rather than penetrate.
•
Durability
– Quality of construction materials is
a significant factor in overall success of
the rainscreen system.
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Slide 16 of 51
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Moisture Management in Construction
MOISTURE MANAGEMENT RATIONALE – BARRIER DESIGN
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Moisture damage is the second leading cause of building damage behind fire.
•
Face Sealed Barrier Design:
– The exterior surfaces are relied upon as the only barrier to water entry.
•
Vented Rainscreen:
– A compartmented air cavity behind the exterior cladding system and the
structural wall, an air barrier system and adequate venting area of the exterior
cladding in relation to the leakage area of the air barrier are necessary
elements.
•
Redundant Barrier System:
– A system of water resistant layers between the exterior cladding to prevent the
entrance of water into the structural wall.
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Slide 17 of 51
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Moisture Management in Construction
RAINSCREEN TECHNOLOGY
WHAT IS A RAINSCREEN?
•
Originally developed for use in masonry construction, a rainscreen is a pressure
equalized airspace between the structural envelope and the exterior cladding created
for the purpose of draining moisture from the assembly.
www.bia.org
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Slide 18 of 51
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Moisture Management in Construction
RAINSCREEN TECHNOLOGY
WHY USE A RAINSCREEN?
•
That notion of a “face-sealed” assembly as
defined in ASTM E-2128 whereby “the
exterior surfaces are relied upon as the only
barrier” (to water entry) has been replaced by
the realization that water is going to by-pass
the exterior cladding and therefore must be
intentionally addressed with a “forgiving”
assembly that manages the water.
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Slide 19 of 51
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Moisture Management in Construction
PRESSURE EQUALIZATION/MODERATION
•
•
Cladding systems are designed to protect the walls of a house from weather exposure
and damage. In practice, however, rain protection is very difficult to achieve because
water can be forced through tiny cracks, joints, or any otherwise insignificant opening in
the cladding system.
The concept of a pressure-equalized rainscreen arises from the fact that wind creates a
pressure differential across cladding systems, which is one of the driving forces that
push water through small openings. To reduce this pressure difference would be to
reduce moisture intrusion.
Effect of Pressure Differences on Walls
•
•
Air will always seek to travel from a place of high pressure to an area of lower pressure.
This basic fact of nature supplies the driving force for moisture penetration behind
cladding. When wind force is exerted on a wall, the air pressure is greater on the front
side of cladding than on the back.
Consequently, the wind will force itself, and the rain with it, behind cladding through any
means possible. Air pressure differential is also the more prominent force in the
movement of water vapor behind cladding (water vapor moves by vapor diffusion to a
lesser degree, the notable exceptions being hot-humid climates or rain wetted walls
experiencing solar heating). With the help of a pressure difference, significant amounts
of moisture can move into a wall assembly, potentially leading to damage of the building
materials and possible mold growth.
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Slide 20 of 51
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Moisture Management in Construction
PRESSURE EQUALIZATION/MODERATION
•
•
Pressure differences can also adversely affect the housewrap or building paper.In the same
way a wind force can create a positive pressure on a wall, a negative pressure can be
created on the opposite side of a house.
In this case, the housewrap or building paper can “balloon” out from a wall, causing the
housewrap or building paper to pull away from its fasteners, improving the chances for air
and water infiltration behind the barrier.
•
Pressure-equalized Rainscreen
•
The theory of a pressure-equalized rainscreen is that wind is allowed to flow into a cavity
behind the exterior cladding, thus equalizing the cavity pressure with the wind pressure. With
the limitation of a pressure difference, the force that causes most rain penetration is
eliminated.
In reality, there is a time lag between the application of the wind load and pressure
equalization in the cavity. Especially if winds are gusting, instantaneous equalization may be
difficult to achieve.
Pressure moderation is a more likely occurrence in these instances. While equalization is
the goal, moderation helps to reduce the possibility for moisture intrusion.
•
•
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Slide 21 of 51
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Moisture Management in Construction
VENTILATION AND DRYING CAPACITY
•
The provision of a vented top and bottom detail in vented, continuous rainscreen
barrier application enables the exchange of air between the cavity and the outside.
Wind pressure applied to the sidewall can induce a convective ventilation flow in
which air enters the top and exits the bottom, or vice versa.
•
Wind load can often increase with the distance away from the ground. In this
situation, higher pressure at the top of the wall forces air into the top vent and out
the bottom.
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Slide 22 of 51
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Moisture Management in Construction
VENTILATION AND DRYING CAPACITY
•
For a reference point, when a wall is subject to 1 Pascal of pressure (which is
common in the field), the cavity can allow 0.017 ft3/min of airflow per square foot of
cladding. When this value is applied to a typical house (2400 ft2 of cladding), a cavity
can provide 4.2 air changes per hour.
•
4.2 air changes per hour is a significant amount of ventilation for a rainscreen cavity.
In terms of drying performance, an airflow of this amount is capable of removing 1.2
gallons of moisture per day from a wall assembly.
•
Note: These values result from the forced ventilation driven by wind. In the absence
of wind, a ventilation flow can still occur due to a stack effect in the cavity (warm air
rises and creates a natural airflow).
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Slide 23 of 51
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Moisture Management in Construction
WHERE TO USE RAINSCREENS
“ Moisture management strategies are
recommended in all climate regions,
and are essential where average rainfall
exceeds 20 inches”.
Joe Lstiburek, P.Eng
Building Science Corporation
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Slide 24 of 51
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Moisture Management in Construction
TRADITIONAL RAINSCREEN ASSEMBLY
•
The traditional way of creating a rainscreen wall:
– Place lathe strips or 1x dimensional lumber, vertically at 8”, 12”, 16”or
24”centers.
– Attach cladding to the wood strips
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Slide 25 of 51
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Moisture Management in Construction
TRADITIONAL RAINSCREEN ASSEMBLY
•
Disadvantages of Traditional Rainscreen Assembly:
– Labor intensive and hard to detail around penetrations.
– Create hot-spots and thermal bridging along stud locations.
– Ballooning of house-wrap leads to air infiltration and reduced air movement in
intended rainscreen cavity.
– Cupping & bowing of furring strips leads to premature failure of coating.
– Wood-to-wood contact traps moisture, supports growth of mold and causes
“ghosting” or vertical telegraphing of furring locations to outside surfaces.
– Inconsistent performance.
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Slide 26 of 51
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Moisture Management in Construction
PRESSURE EQUALIZED RAINSCREEN WALL PRINCIPLES
•
The difference in air pressures across the exterior cladding is a significant force which
causes infiltration of air and water on windward facades. Air and moisture can infiltrate
through units, mortar joints, hairline cracks, poorly bonded surfaces and other
openings that exist or develop over the life of the structure.
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Slide 27 of 51
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Moisture Management in Construction
MOISTURE MANAGEMENT METHODS
•
“Void space technology” responds to current construction practices by utilizing a 3dimensional plastic matrix that provides a vented continuous rainscreen.
•
Typically, the rainscreen barrier is a void space matrix that diverts moisture into it
and provides channels to carry the moisture out of the system.
•
Additionally, the vented continuous barrier matrix allows air to flow through the
system to provide drying and pressure equalization.
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Slide 28 of 51
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Moisture Management in Construction
MOISTURE MANAGEMENT METHODS
•
A vented and continuous rainscreen barrier may
be placed behind a wide variety of exterior finish
materials including:
– Wood Cladding
– Fiber Cement Siding
– Stucco/Stone Veneer
– Brick Veneer
– EIFS
– Vinyl Siding
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Slide 29 of 51
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Moisture Management in Construction
MOISTURE MANAGEMENT METHODS
Wood Cladding
•
Without a means to dry wood cladding, trapped
rain and water vapor can result in an array of
problems. With the external surface open to
ventilation and solar drying and the backside
exposed to trapped moisture, unequal shrinkage
and swelling can occur. This gives rise to
bowing, cupping, splitting, warping, and even
paint and stain failure.
•
Rot and decay is initiated by an increase in
moisture content. Excess moisture on wood can
attract damaging termites, carpenter ants and
beetles. Unventilated moisture can also create a
breeding ground for mold, mildew and fungi. In
addition, wood siding contains water-soluble
extractives that can degrade the water
repellency of housewraps and building paper.
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Slide 30 of 51
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Moisture Management in Construction
MOISTURE MANAGEMENT METHODS
Wood Cladding
•
By allowing air circulation behind the cladding
material, a vented, continuous rainscreen barrier
can help to promote an even drying of the wood,
decreasing the potential for distortion. The
drainage and ventilation provided can reduce the
opportunity for rot and decay.
•
A vented, continuous rainscreen barrier
decreases the amount of trapped moisture in a
wall assembly, thereby reducing the potential for
mold growth. Additionally, the air-space created
helps to protect many housewraps from the
damaging effects of surfactants leaching from the
wood siding.
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Slide 31 of 51
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Moisture Management in Construction
MOISTURE MANAGEMENT METHODS
Fiber-Cement Siding
•
Fiber-cement siding products create a tight
exterior cladding system that allows for little air
movement. If any moisture gets behind the
siding, there is no sufficient mechanism to dry
or drain the wall assembly. Caulks will break
down over time, allowing some rainwater to get
in.
•
Moisture vapor that comes from inside the
house will enter the wall cavity and can also be
trapped by this tight system.
•
Excess moisture leads to rot and decay, attracts
damaging insects, ruins finishes, and can
destroy the aesthetic qualities of the sidewall.
The presence of moisture trapped in the dark
wall assembly can also breed mold and mildew.
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Slide 32 of 51
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Moisture Management in Construction
MOISTURE MANAGEMENT METHODS
Fiber-Cement Siding
•
A vented, continuous rainscreen barrier employs
ventilation and drainage along the backside of the
cladding to help reduce the amount and time
moisture is trapped in the wall assembly. This, in
turn, can improve the service life of fiber-cement
siding.
•
A vented, continuous rainscreen barrier provides a
ventilation path to help dry interior or exterior
moisture vapor trapped behind the siding that
otherwise could not drain.
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Slide 33 of 51
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Moisture Management in Construction
MOISTURE MANAGEMENT METHODS
Stucco/Stone Veneer
•
Stucco and stone veneer are both porous materials
that allow moisture in and out of the wall cavity.
Moisture can get behind the cladding through
capillary suction, small cracks, improper installation
methods and wind driven rain. Moisture in stucco or
stone veneer systems may even originate from the
cladding material itself if the application coats are
applied too quickly.
•
Stucco has also been found to damage the
housewrap or building paper. Surfactants in stucco
leak out and degrade the water repellency of the
weather barrier allowing water intrusion and moisture
damage.
•
A vented, continuous rainscreen barrier creates an
airspace behind the stucco or stone veneer wall
system that is open to outside air. It acts as a
capillary break and a drainage medium for any water
that penetrates into the wall system.
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Slide 34 of 51
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Moisture Management in Construction
MOISTURE MANAGEMENT METHODS
Stucco/Stone Veneer
•
A vented, continuous rainscreen barrier
creates a ventilation path to dry moisture
trapped behind cladding. It also provides a
separation between the weather resistive
barrier and the stucco to protect the
housewrap or building paper from surfactant
damage.
•
Note: Certain house wrap materials
designed with a corrugated face to facilitate
moisture drainage. Typically these house
wraps are not designed as a pressure
equalized system.
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Slide 35 of 51
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Moisture Management in Construction
MOISTURE MANAGEMENT METHODS
Brick Veneer
•
Brick veneers have posed a challenge to installers and designers because of moisture intrusion behind
the cladding, forcing the Brick Institute of America to recommend an airspace behind the brick. Brick and
mortar are porous materials that act as a reservoir when wetted by wind-driven rain. Cracks and
deteriorating caulk also allow for water penetration behind the cladding.
•
The installation of an airspace behind a brick veneer has often failed to provide relief from moisture
intrusion because of mortar droppings in the cavity. The mortar clogs the airspace, allowing for moisture
travel from the brick to the sheathing.
www.bia.org
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Slide 36 of 51
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Moisture Management in Construction
MOISTURE MANAGEMENT METHODS
Brick Veneer
•
A vented, continuous rainscreen barrier is a moisture eliminating system that creates a
ventilation and drainage space behind brick veneer to allow for the escape of moisture to the
outside.
•
In contrast to an open airspace, a vented, continuous rainscreen barrier not only manages
trapped moisture, it also provides a uniform, consistent barrier to water bridging from the brick
veneer to the inner sheathing due to mortar droppings.
www.bia.org
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Slide 37 of 51
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Moisture Management in Construction
MOISTURE MANAGEMENT METHODS
EIFS
•
Void space technology in the form of a
vented, continuous rainscreen barrier is now
available from many EIFS manufacturers
•
The insulation board should be
mechanicallly fastened over the vented,
continuous rainscreen barrier to ensure an
open cavity for ventilation and drainage
•
Note: Several EIFS manufacturers have
available a grooved backed insulation to
provide channels for moisture drainage.
Typically these are not designed as a
pressure equalized system.
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Slide 38 of 51
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Moisture Management in Construction
MOISTURE MANAGEMENT METHODS
Vinyl Siding
•
Vinyl is a popular siding alternative for easy
maintenance and water resistance. Unfortunately,
vinyl siding is an imperfect barrier that allows
moisture penetration at overlaps, cracks, and edges
of windows and doors. Along with vapor escaping
from inside a home, this moisture can pose a
danger to the integrity of the sheathing.
•
Vinyl is a loose cladding with built-in weep holes to
help remove moisture from the wall. A vented,
continuous rainscreen barrier is intended to add
redundant protection to this system to ensure
moisture removal in areas subject to high
precipitation.
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Slide 39 of 51
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Moisture Management in Construction
MOISTURE MANAGEMENT METHODS
Vinyl Siding
•
By providing a ventilation path to outside air, a vented, continuous rainscreen
barrier can help reduce the amount of rain driven behind vinyl by moderating the
pressure across the cladding.
•
Any incidental moisture trapped behind the siding can be safely drained and
ventilated from the wall system.
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Slide 40 of 51
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Moisture Management in Construction
PAINTS AND STAINS
•
The average life span of paints and stains can be
significantly reduced as a result of trapped moisture in a
wall assembly. The normal life of a finish can be shortened
by discoloration (staining, bleeding), or degradation (peeling,
blistering, cracking).
•
Trapped moisture in a wall can damage and decay siding
material. Swelling, shrinking, cupping, and warping of siding
will cause a paint or stain to peel, blister and crack. Interior
moisture vapor drive from a home has also been known to
cause paint and stain failure as it is drawn through the siding
in the drying process.
•
By protecting the siding from excessive moisture and
accelerating the drying process, a vented, continuous
rainscreen barrier has been recognized by many major
paint/stain manufacturers to help preserve the finish and
ensure proper service life of paints and stains.
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Slide 41 of 51
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Moisture Management in Construction
SURFACTANTS
•
Surfactants are soap-like chemicals that degrade the water
repellency of materials in order to help remove dirt and
grime from surfaces.
•
Unfortunately, surfactants exist in the building envelope,
impairing the function of housewraps and building paper which
act as liquid water barriers.
•
Surfactants found in wall systems can be traced to three main
sources: wood siding, stucco, and detergents used in
pressure washing. They can decrease the water resistance of
housewraps and building paper allowing water intrusion which
can lead to moisture damage of the siding, sheathing, and
wall system.
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Moisture Management in Construction
SURFACTANTS
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Enough surfactant may also cause a paint or stain finish to
deformulate and fail to perform its designed functions, or
cause staining and discoloration by ruining its water repellent
characteristic.
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A vented, continuous rainscreen barrier provides an extremely
effective preventive solution to the surfactant issue by creating
a continuous airspace for ventilation and drainage between
the cladding and the housewrap or building paper.
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By isolating the housewrap and building paper from the siding,
vented, continuous rainscreen significantly reduces surfactant
contact between the building materials.
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Moisture Management in Construction
SHEATHING
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Sheathing is basically the shell of a home. It must encase
and protect the house while being able to withstand certain
external forces, such as wind load and seismic activity. As
with most building materials, moisture can attack and
damage sheathing, compromising the structural integrity of
the wall assembly.
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Plywood is a woodbased product that can only deter the
damaging effects of moisture with the help of external drying.
If plywood is exposed to trapped moisture for an extended
period of time, fungi and insects can create structural and
health concerns. A vented, continuous rainscreen barrier
provides a means for this trapped moisture to drain and
evaporate from the building envelope.
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Moisture Management in Construction
SHEATHING
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Oriented strand board (OSB) responds more slowly to
changes in relative humidity and exposure to liquid water. It
takes longer for water to soak OSB and conversely, once
water gets into OSB, it is very slow to leave which results
in rot. OSB is also subject to cupping and warping
because it expands faster around the perimeter of the
panel than it does in the middle. A vented, continuous
rainscreen barrier helps to protect OSB sheathing by
managing the moisture that would otherwise be trapped in
the wall assembly.
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Foam sheathing’s vapor permeability is much lower than
other sheathing systems. Consequently, water that does
penetrate behind cladding tends to stay trapped for longer
periods. A vented, continuous rainscreen barrier allows an
escape for this moisture, thereby lessening the opportunity
for moisture damage to occur. Polystyrene and extruded
polystyrene foam sheathing have also been known to
degrade from exposure to surfactants. A rainscreen barrier
creates separation and induces drying to protect the
sheathing from surfactant degradation.
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Moisture Management in Construction
WEATHER-RESISTIVE BARRIERS
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Housewraps and building papers are subject to a number of factors—including
unventilated moisture, wind pressure, and surfactants exposure—that can degrade
and weaken their ability to perform their designed function. A vented, continuous
rainscreen barrier has been designed to preserve and enhance the performance of
weather resistive barriers.
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Housewraps and building papers can separate from a wall when wind pressure is
exerted causing the paper to pull away from its fasteners and improving the chances
for air and water infiltration in the wall system. Housewraps and building papers are
also susceptible to damage and degradation caused by surfactants in the wall
assembly which are drawn out of wood cladding and stucco by moisture .
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Moisture Management in Construction
WEATHER-RESISTIVE BARRIERS
•
A vented, continuous rainscreen barrier creates separation between the weather
resistive barrier and the cladding to create a capillary break and to increase the rate
of drying, thus preventing moisture accumulation on the housewrap or building paper.
A vented, continuous rainscreen barrier provides a support layer between the
cladding and housewrap or building paper to hold the paper in place and reduce the
effects of wind driven separation.
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A vented, continuous rainscreen barrier provides an airspace to facilitate drainage
and drying of surfactant-carrying water and to prevent surfactants from contacting
and degrading the weather-resistive barrier.
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Moisture Management in Construction
MOISTURE MANAGEMENT METHODS
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Top and bottom of vented rainscreen barrier cavity must be ventilated to allow
moisture to escape and to equalize the pressure in the drainage cavity.
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Moisture Management in Construction
MOISTURE MANAGEMENT METHODS
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Detailing around penetrations is critical
to the success of any vented
rainscreen barrier system.
•
Flashing the window or door assembly
into the moisture barrier system must
be clearly detailed on the drawings and
coordinated with the vented rainscreen
barrier system.
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Moisture Management in Construction
SPECIFICATION CONSIDERATIONS
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Vented rainscreen barrier materials maybe specified in a narrow-scope section such
as Section 07460 – Sidewall Rainscreen Membrane.
– It is critical that this section be cross-referenced to other sections utilizing or
interfacing with the vented rainscreen barrier.
– This has the advantage of indicating materials and methods in one place.
– It has potential disadvantage of not being picked up by each of the bidders in
whose assemblies it is used.
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Alternatively, vented rainscreen barrier materials maybe specified in each of the side
wall system assemblies utilized on the project.
– The advantage is that each bidder must include the vented rainscreen barrier in
their work.
– A disadvantage maybe that modifications to individual sections could create
conflicts or differences in how the vented rainscreen barrier material is installed.
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Moisture Management in Construction
CONCLUSION OF THIS MODULE
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If you desire CSI and/or state licensing continuing
education credits, please click on the button below to
commence your online examination. Upon successful
(80% or better) completion of the exam, please print the
certificate indicating your completion of the course.
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For additional knowledge and post-seminar assistance,
please avail yourself to the Seminar Discussion Forum
(click on link above and bookmark in your browser).
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If you have a colleague that might benefit from this
seminar, please let them know.
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Last, revisit AEC Daily and download additional
seminars available at the Online Learning Center.
©2004 Benjamin Obdyke. The
material contained in this course
was researched, assembled, and
produced by Benjamin Obdyke and
remains their property. Questions or
concerns about this course should
be directed to the instructor.
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