Are water resistive barriers and building wraps air barriers?

Referred to in the building code as a water-resistive barrier (WRB), its main goal is to keep liquid water out of the structural part of a building. At the same time, the “WRB” must allow water vapor to pass through so the framing or sheathing can dry to the exterior if it gets wet. WRB material types include:

• paper or felt type,
• polymeric type,
• mechanically attached or fastened to the exterior side of stud walls – using staples, nails capped screws, and battens.

These types of WRB’s, when installed, are lapped to neighboring sheets or flashings, which would then require tape or caulk to seal the envelope effectively.

WRB’s that fall into the building wrap category are primarily spun bonded polyolefin (non-perforated and woven/perforated), or engineered fabric. Most building wraps or felt papers have the ability to stop liquid water while remaining vapor permeable to water vapor. These are generally relatively low-cost water-resistive barrier options.

What is an air barrier?

Air barriers are critical to achieving building energy efficiency and indoor environmental quality and satisfying code requirements. It’s important to remember that an air barrier is not a single product but rather a system of products producing an air barrier assembly.

Most building wraps are best used to protect the wall sheathing from any wind-driven rain that gets past the cladding and are not typically air barriers. That said, some building wraps have been tested and are marketed as air barriers, and depend on air tightness being maintained around seams, transitions, and window openings to help prevent unwanted air infiltration. For various reasons, it can be challenging to effectively install building wraps as a continuous air barrier in commercial construction projects.

Commercial building WRBs, which are also effective air barriers, are typically self-adhered sheet membranes or fluid-applied membranes that are used in conjunction with flashings and sealants to create a monolithic building envelope.

Fluid-applied membrane systems can be vapor-permeable or vapor-impermeable and can range from 7 to 125 mils dry film thickness. They can be spray-, roller- or trowel-applied and fully adhere to the substrate. They are also effective on rough substrates or substates that present a lot of existing penetrations or complex geometries.

Fully-adhered or self-adhered membrane systems are best used on smooth substrates and create a fully sealed building envelope when installed with the proper flashing and sealant. The mil thickness is factory controlled and the complete system helps seal out moisture and air.

Henry offers a complete portfolio of fluid applied and self-adhered air barrier membranes, as well as flashings, sealants and accessories designed to work together to create an effective building envelope system. Whether you project calls for non-permeable or permeable, and no matter the substrate you are working with, Henry is your one-stop-shop for a complete air barrier system.

If you need help selecting the right water resistive barrier for your next project, contact a trusted Henry advisor.