Essentials for Air Barrier Systems in Building Construction

U.S. Department of Energy statistics show that buildings account for 40% of all U.S. primary energy consumed. And 35% of the energy those buildings use goes to heating, ventilation, and air conditioning. Fortunately, according to the NIST, air barrier systems in building construction can reduce building heating and cooling energy demands by 30% regardless of climate zone.

Of course, boosting building energy efficiency is just part of what an air barrier does. By preventing uncontrolled airflow, an air barrier also helps protect indoor environmental quality and the long-term health of the building.

Air, vapor, or water resistive barriers?
Because even the experts confuse the differences between air, vapor and water resistive barriers, here are some basic definitions of these terms:

• Air barriers resist air leakage and form a continuous plane around a building to prevent uncontrolled airflow in and out of the building envelope.
• Vapor barriers limit the amount of water vapor diffusion through the wall as a result of different vapor pressures. Vapor barriers still have to be continuously sealed and free of holes.
• Water-resistive barriers (WRB) keep liquid water from entering the building enclosure. Combined with flashing and other materials, WRBs ensure that there is a completely sealed assembly to direct liquid water to the exterior.

Air barrier basics
Air barriers help control airflow into and out of the building and are a critical part of the building envelope. Along with reducing building energy consumption, air barriers guard against threats to long-term building performance, since uncontrolled airflow can lead to scenarios that reduce building life and the quality of the building environment. An effective air barrier performs several jobs at once:

• Manages bulk water
• Limits deterioration
• Controls air leakage
• Maximizes thermal performance
• Manages condensation
• Meets modern building codes

A system by design
An air barrier is not a single product, but rather a system of products – that is, an air barrier membrane, a flashing, a sealant and required accessories. Together, air barrier system components are meant to form a continuous plane of airtightness around the building enclosure. In order to be effective, all air barrier components must be chemically compatible, properly installed and designed to meet specific project requirements.

Air barrier types
In recent years commercial construction has seen a dramatic shift from mechanically fastened to fully adhered air barriers, which are available in two basic types:

• Self-adhered sheet air barriers – With no need for mixing or spray equipment, self-adhered sheet applied air barriers help simplify installation. Ideal for use with open joint claddings, they also offer manufacturer-controlled thickness and the ability to bridges gaps/cracks without additional detailing. Self-adhered sheets require caution during installation to prevent wrinkles/bubbles and may require lap sealing.
• Fluid-applied air barriers – Offering spray, roll and trowel application options, fluid applied membrane air barriers eliminate seams and make installation easier on complex geometries. Ideal for irregular substrates, many fluid-applied air barriers feature quick-curing technologies to keep schedules on track. Overspray caution and thickness verification may be required.

So, which fully adhered air barrier type will be best for your next building? Henry Company can help you weigh the pros and cons of a self-adhered or fluid applied air barrier against the many specifics of your project. Whatever questions you may have about air barrier systems in building construction, please don't hesitate to schedule a meeting with one of our reps today.