Water-Resistive
Barriers/Housewraps
What is a Housewrap?
A housewrap, or
water-resistive barrier, is a thin membrane layer typically 5 to 15
mils thick (.005 to 0.015 in. or 0.13 to .38 mm) which is intended
to resist liquid water that has penetrated behind the exterior
cladding from further intruding into the exterior wall assembly.
Housewraps come in a variety of widths and lengths as well as a
variety of materials. These materials consist of polyolefin-based
sheets (plastic) and can include spun-bonded (fibers), cross-woven
(tapes), film (sheets) or a combination thereof.
A housewrap is different
than Grade D building paper (paper-based). Most commercially
available polymeric housewraps are highly moisture-resistant and
therefore, do not absorb water like typical Grade D or felt building
papers. Polyolefin housewraps are typically stronger than Grade D or
felt building papers, thus they tend to have better durability than
conventional building papers.
What Does A Housewrap
Do?
The primary function of
a housewrap is water resistance. Housewraps are hydrophobic
(designed to resist bulk water penetration). A housewrap deflects
water and channels it down the surface of the exterior wall. In
addition, housewraps allow moisture vapor to move freely, thus
reducing the potential for condensation build-up, which reduces the
likelihood of rot/degradation.
Housewraps function as
air retarders. Some Housewraps may also meet the requirements for an
Air Barrier Material (0.02 L/s·m² @ 75 Pa or 0.004 cfm/ft 2 @ 1.57
psf ) reducing air permeance when evaluated in accordance with
ASTM E 2178. Housewrap
materials that qualify as air barrier materials must be installed in
strict accordance with the manufacturer’s instructions in order to
perform as required.
How Do Housewraps Work?
A Housewrap decreases
the air infiltration into the wall cavity, hence allowing the
insulation in the wall cavity to function as it was intended, by
trapping air and creating a dead air space.
Housewraps also resist
bulk water penetration resulting from wind-driven rain that
penetrates the exterior cladding, ultimately migrating into a
well-built wall cavity. Housewraps enable walls to dry out by
allowing moisture vapor to escape when liquid water evaporates.
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