Codes and Legislation Relating to Air Barriers

Air barrier systems provide several advantages for building projects, including increased interior comfort, durability and energy efficiency. With these attributes, they are suitable for a variety of applications in various climates.

Air barriers have the potential to reduce air leakage to acceptable levels for less than $1.50/square foot of gross building area, and are often specified for buildings. Air barriers are typically regulated through energy codes, which recognize the importance of airtight buildings and energy efficiency. As of early 2006, several states have developed existing and pending legislation on air barriers, as well as compliance criteria.

The 1995 National Building Code of Canada (NBC code) requires a continuous air barrier for all commercial buildings. Massachusetts was the first state to adopt an energy code, in 2001, which is similar to the NBC code, and requires a continuous air barrier for commercial buildings. Wisconsin adopted an energy code in 2003. Minnesota is developing an energy code in early 2006, with similar compliance criteria as the Massachusetts energy code. In addition, as of 2003, the Envelope Design Guidelines for Federal Office Buildings and Multi-Family High Rise Residential Buildings require air barriers.

As air barriers are better understood and the benefits are documented, more jurisdictions will likely be following suit. In 2005, the American Society of Heating, Refrigeration and Air-Conditioning Engineers (ASHRAE) approved an amendment to the ASHRAE 90.1 model energy code that would require an air barrier for most commercial buildings in most climate zones. With their clear advantages and the imminent code requirements, it's critical that architects understand the air barrier functions and benefits, and how to specify them.

The Physics of Air And Moisture Transport Through The Building Enclosure

To gain a proper working understanding of the role of air barriers in building enclosures, some basic terminology and fundamental physics must first be defined. The building enclosure, also known as the building envelope, refers to the part of the building that physically separates the interior conditioned space from the exterior environment. Its main function is to control all loadings due to separation of the two environments, the flow of mass and flow of energy. Air barriers are an important component of the building enclosure.