Air barriers are designed to control the climate within a structure. Air barriers are systems of materials that separate a conditioned space from an unconditioned space. A conditioned space usually refers to the internal environment of a structure and an unconditioned space refers to the external environment. However, a garage can also be considered as an unconditioned space. In this case, applying an air-barrier can serve as a gas barrier, protecting the home from toxic fumes. An air barrier is designed to control the climate and air-pressure of a conditioned space, such as the flow of air and moisture into and out of a home, building, or structure.
Air Movement From an Unconditioned to a Conditioned Space
Heat naturally flows from warmer to cooler areas. It wants to flow and spread out to areas with less heat. Congratulations, you have just learned the second law of thermodynamics and some building science! Movement of air from an unconditioned (little or no heat) to a conditioned (heated) space can occur for many reasons, such as air leaks from any unsealed structures, such as walls, windows, floors, ceilings, flue vents, crawl spaces, vents, cracks and cavities. Enormous amounts of heat can be lost if the air barrier is weak. That translates into soring heating and air-conditioning costs.
Air Carries Moisture
Air carries moisture with it. Control the flow of air and you control the moisture. Control the moisture, and you reduce or eliminate the growth of mold as well as prevent rusting. Moisture and mold can cause damage to a structure and potentially cause health problems.
How to Detect an Air Leak in a Conditioned Space
There are two main methods for testing: Using a portable fan and the HVAC system, or heating and cooling system. Both systems create a pressure difference that can be measured. The first method is most often used for smaller structures such as homes and small buildings. The second method is most often used for larger buildings or structures.
Here is a neat little trick to check for air leaks: Use a fog machine! There are the inexpensive fog machines typically used during Halloween to create that eerie graveyard look. This is referred to as the "fog test". Another way to detect temperature variations in a conditioned space is using a thermal gun.
Air barriers can entail a system of materials as opposed to using a single material. Air barrier systems are comprised of air-barrier materials which are used as components to create an air-barrier assembly. This assembly is then used to create the air-barrier system.
There are many types of air barrier systems on the market. They consist of a “sandwich” of materials designed to provide the best barriers against air leaks.
Materials used to build a structure have unique properties. Poured concrete, glass, drywall, plywood, cellulose, ridged and sprayed polyurethane, peel and stick rubber can make excellent barriers if they are in good shape. However, these materials are only good if there are no air leaks around them. Caulking is not a long-term fix as it cracks over time from weathering.
Most air leaks occur at the seams or cracks between different materials. Examples include where the mudsill framing meets a foundation, where walls meet ceilings and where floors meet walls. Gaps around windows and doors also contribute to air leaks; however, the most significant air leaks usually occur in hidden areas. Because theses leaks are not as obvious, most homeowners are often unaware of their existence.
Areas Most Often Poorly Sealed That Contribute to Significant Air Leakage:
- Holes cut for plumbing--under sinks, tubs and showers
- Cracks between flooring and baseboards
- Utility chases that hide pipes or ducts
- Plumbing vent-pipes
- Kitchen soffits over wall cabinets
- Basement rim joist areas
- Fireplace surrounds
- Recessed lighting
- Cracks between ceiling-mounted duct boots and ceiling drywall
- Poorly weather-stripped attic access hatches
- Cracks between partition top plates and drywall
- Gaps around windows and doors
For additional information on Air Barriers, contact the ABAA (Air Barrier Association of America).
Note: This article is intended only as a simplified over-view and does not replace or alter OSHA regulations. Always consult with OSHA for current standards.