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MEEF - Middle East Economic Engineering - Articles  - Air Barriers  previous page

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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