Water-Resistive
Barriers/Housewraps
Benefits Of Using
Housewraps?
A
properly installed housewrap system (which includes proper flashing
and sealing around penetrations) will vastly improve the overall
thermal efficiency and performance of the building’s wall system.
While housewraps have no intrinsic R-value, they enhance the thermal
performance of a wall system by reducing air leakage..
Housewraps enhance the
thermal performance of a wall system by reducing air leakage through
the wall cavity, therefore increasing the comfort level of a home or
building. They are also effective at protecting the wall system
components from exposure to bulk water. Finally, housewraps assist
in keeping wall cavities dry by providing a secondary drainage
plane, which reduces the potential for rot/degradation.
As an air retarder, housewraps reduce convective wind-washing
against sheathings and air infiltration into stud wall cavities. As
part of an air barrier assembly, a housewrap can reduce drafts,
increase comfort and reduce energy use by decreasing the amount of
non-conditioned air entering and exiting conditioned wall cavities.
In fact, the average 2500 square foot house (232 m 2) has more than
½ mile (806 m) of cracks and crevices which are open to wind and
wind-driven rain.
Housewraps reduce wetting potential by controlling the bulk movement
of moisture-laden air into the wall cavity. Housewraps are vapor
permeable and assist in the overall drying potential of the wall
should this liquid moisture or condensation accumulate in the wall
cavity.
Commercially available housewrap materials are manufactured in a
range of permeance levels, which allow for a wide range of selection
to accommodate various wall designs.
Housewraps are a durable option over conventional building paper.
They resist:
-
Handling damage both
on the job site and during installation
-
Wind damage during
construction (prior to installation of exterior cladding)
-
UV degradation
-
Failure due to
incompatibilities with common construction materials
-
Expansion/contraction effects caused by wetting, drying, heating
& cooling.
Housewraps perform as a drainage plane by deflecting water and
channeling it down the surface of the exterior wall. This allows the
housewrap to act as a secondary barrier to bulk water that has
penetrated the exterior plane, thus reducing the likelihood of
building rot/degradation.
Why Is It Important for
Walls To Breathe?
As the seasons change,
the moisture content of the outdoor air changes. If moisture vapor
becomes trapped in the wall cavity of a home or building, the
resulting condensation can potentially lead to growth of mold,
mildew and rotting of some building materials. Housewraps allow
potentially harmful moisture vapor to move into and out of a wall
system so that it does not become trapped.
Can You Use Housewraps
Under Any Exterior Façade?
Housewraps can be used
under most exterior cladding materials. In fact, the International
Building, Residential and Energy Codes require the use of
water-resistive barriers (housewrap or felt building paper) in
exterior walls. There are special requirements for some applications
or systems, such as conventional stucco systems, which requires more
than one layer of a water-resistive barrier when wood sheathing is
used.
How Do I Install A
Housewrap System Properly?
A housewrap should be
installed in accordance with the manufacturer's installation
guidelines. Consult each manufacturer’s literature for details.
The entire building
should be wrapped, including exterior and interior corners and gable
end walls. Building codes require that all vertical and horizontal
seams be overlapped a minimum of 6 and 2 inches respectively in a
shingle application.
Taping of housewrap
seams can provide additional protection against moisture intrusion
and air leakage while maintaining durability. However, since taping
of seams is not a building code requirement, it is typically
considered optional. There are specific instructions to be followed
when installing a housewrap as an air barrier, which include taping
of seams, sealing around all penetrations and use of window flashing
materials. A modified "I" pattern is typically cut in the housewrap
at window openings and the excess material is folded inside the
rough opening and attached to a framing member. Use of window
flashing materials is encouraged.
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