What is a Water-Resitive Barrier?

A water resistive barrier is a thin membrane, 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.

Function of a Water Resistive Barrier

A properly installed water resistive barrier (which includes proper flashing over doors and windows, continuity at seams, and sealing around penetrations) will improve the overall moisture efficiency and performance of the home or building’s wall system by providing a secondary moisture drainage plane. Water resistive barriers resist bulk water penetration and wind-driven rain that penetrates the exterior cladding from intruding into the wall assembly. Water will be channeled down the outside surface of the water resistive barrier, thus reducing the potential for condensation build-up in the wall assembly which reduces the likelihood of moisture problems, rot and degradation.

Water-resistive barriers come in a variety of widths and lengths as well as a variety of materials. These materials consist of polymeric-based sheets (plastic) and can include spun-bonded (fibers), cross-woven (tapes), film (sheets) or a combination thereof.

A water resistive barrier is different than Grade D building paper (paper-based). Most commercially available polymeric-based water-resistive barriers are highly moisture-resistant and therefore, do not absorb water like typical Grade D or felt building papers. Polymeric water-resistive barrier are typically stronger than Grade D or felt building papers, thus they tend to have better durability than conventional building papers.

ABAA Evaluated Water-Resistive Barriers

Why Is It Important for Walls To Breathe?

Water resistive barriers are typically vapor permeable, which is generally desirable because it allows for drying of any moisture that accumulates in the wall assembly. Water resistive barriers are manufactured in a range of permeance levels, which allow for a wide range of selection to accommodate various wall designs.

Can You Use Water-Resistive Barriers Under Any Exterior Façade?

Water resistive barriers can be used under most exterior cladding materials. In fact, the International Building, Residential and Energy Codes require the use of water-resistive barriers or felt building paper in exterior walls. There are special requirements for some cladding applications or systems which requires more than one layer of a water resistive barrier. See cladding manufacturers for more information.

How do I Install a Water Resistive Barrier Properly?

A water-resistive barrier should be installed in accordance with the manufacturer's installation instruction, consult manufacturer's literature for further details.

Typically a modified "I" pattern is cut in the water resistive barriers at window openings and the excess material is folded inside the rough opening and attached to a framing member prior to a window being installed. The entire building or dwelling should be wrapped, including corners and gable end walls. Building codes require that all vertical and horizontal seams be overlapped a minimum of six and two inches respectively in a shingle application. Taping of water resistive barrier seams can provide additional protection against moisture intrusion while maintaining durability. However, since taping of seams is not a building code requirement, it is typically considered optional and a good building practice.

Refer to ASTM E 2112 or the ABAA Water-Resistive Barriers Installation Guide for further details.

The ABAA Water-Resistive Barriers Committee has produced two videos to assist building officials, design professionals and installers when using water resistive barriers in buildings or dwellings. The technical video presentation covers the properties of the material and the installation video covers key installation criteria.

Click here to view the videos.

Are Water Resistive Barriers the same as Air Barriers?

A water resistive barrier shall exceed a test result of 0.02 L/(s • m²) @ 75 Pa pressure difference (0.004 cfm/ft² @ a pressure difference of 1.57 psf or 0.3 inches of water) when tested in accordance with ASTM E2178 to be classified as a air barrier material. There are specific instructions to be followed when installing a water resistive barriers as an air barrier, which includes mandatory taping of seams, sealing around all penetrations including inside window and door rough openings. See manufacturer for more information on application details.