Masonry Magazine June 2005 Page. 28
AIR BARRIERS
How to Determine the Right Air Barrier for You
By Lisa Petsko
Sto Guard Associate
Market Manager,
Sto Corp.
It can be confusing at times to determine what type of air barrier is the best choice when constructing a home or building. According to the Air Barrier Association of America (ABAA), by definition, air barrier systems are a component of building envelope systems that control the movement of air into and out of buildings. There are many types of air barriers to choose from, and there are many important factors to consider when determining the best barrier.
WAM!: Water, Air and Moisture
Using an air barrier system will result in energy cost savings, as well as reduce the amount of airborne pollutants that result from the combustion of energy producing fuels. The United States Department of Energy concluded that up to 40% of the energy consumed to heat or cool a building is due to air leakage into and out of buildings. A properly installed air barrier system will substantially reduce the amount of air leakage of a building envelope system, thus reducing the building's energy consumption.
Water accumulation in building envelopes is a consideration to weigh when choosing the right barrier system. Water is stealthy and has many ways of penetrating the building envelope. Wind can drive rain through tiny cracks or holes in materials. Capillary action at cracks, holes or in porous materials draws water toward the interior. And water vapor transported by air or by diffusion can condense on cold surfaces hidden within the building envelope.
According to several studies completed in the last decade, air leakage in particular has proven to be a significant potential source of condensation and moisture accumulation in building envelope assemblies. Thus, in addition to preventing water intrusion with design and construction details that protect against wind-driven rainwater entry, minimizing airflow through the building envelope with an air barrier system is also important. An air barrier system that reduces air leakage and is waterproof, is an efficient way of preventing moisture deterioration of building materials.
U.S. & Canadian Codes
Energy codes in the United States have begun to require airtightness of the building envelope, but they are not specific about levels of air permeability. Various states are considering duplicating the Canadian air barrier code into their state codes. Massachusetts and Wisconsin are the only two states with air barrier requirements at this time. However, several states have passed ASHRAE 90.1, considered the definitive guideline for achieving energy.