Inadequately sealed building envelopes can lead to the movement of unconditioned air into and out of conditioned spaces. This process, known as air leakage, decreases the comfort of a building by allowing moisture, drafts, and undesired noise to enter. It applies to any holes, cracks, or gaps in the building envelope. It is important to control air movement in buildings because research indicates that air leakage can cause huge energy losses, accounting for up to a third of a home’s energy use. Air leakage may also reduce indoor air quality by permitting dust and airborne pollutants to infiltrate the building.
A building envelope constructed with proper air sealing can provide many benefits, including:
- Increased comfort: A tighter building envelope reduces the amount of unconditioned air, drafts, noise, and moisture that enter your home. Proper air sealing will also minimize temperature differences between rooms. As a result, tight envelopes can maintain a more consistent level of comfort throughout a house.
- Improved indoor air quality: A tighter building envelope reduces the infiltration of outdoor air pollutants, allergens, dust and radon as well as moisture infiltration from outdoor air in humid climates. Properly sealing the building envelope will also eliminate paths for pests to enter.
- Lower utility bills: Air leakage accounts for 25% to 40% of the energy used for heating and cooling, hampering the performance of other building systems, including HVAC, fenestration, and insulation. All building systems must perform well together to optimize the energy efficiency of a home.
- Fewer condensation problems: In hot, humid climates, moisture can enter into wall cavities through exterior cracks, resulting in mold and mildew problems that can lead to costly damage to framing and insulation. In cold climates, gaps in the interior walls allow moisture from warm indoor air to enter wall cavities and attics, which can condense on cold surfaces and lead to similar damage. Proper air sealing can significantly reduce the incidence of these problems.
Building code officials must be aware of the requirements covered in the energy code and ensure that:
- Correct insulation is used to prevent air leakage around the building envelope
- They are aware of the Thermal Bypass Checklist (if applicable)
- There is caulking around all windows, skylights and doors
- They check all bypasses into unconditioned spaces, such as attic hatches, stairwells, recessed lighting fixtures, and around bathtub enclosures, all of which are notorious for air leakage
Standard issues/concerns that arise include:
- Contractor/sub-contractor closing off an area yet to be checked
- Not sealing where different building features meet
Requirements covered in Section 402.4 are mandatory for all climate zones.
The 2009 IECC code improved requirements for air leakage control by mandating compliance with either a visual inspection option or a testing option. The 2006 IECC made some minor improvements over the 2003 version, such as clarifying the rather ambiguous language regarding which areas required sealing and adding provisions for recessed lighting and sealed dampers for ventilation equipment (bath and kitchen fans, primarily).
Residential Policy Options
Taken from proposals for the 2012 IECC:
- Exterior thermal envelope insulation for framed walls shall be installed in substantial contact and continuous alignment with building envelope air barrier. Breaks or joints in the air barrier shall be filled or sealed. Air permeable insulation shall not be used as a sealing material. Air permeable insulation shall be inside of an air barrier.
- Meeting the Air Leakage Requirements of the 2012 IECC
- Challenges of Achieving 2012 IECC Air Sealing Requirements in Multifamily Dwellings
- BSD-104: Understanding Air Barriers | Building Science Corporation
- Air Barriers in the 2009 IECC | Kenergy
- Retrofit Techniques and Technologies: Air Sealing
A Guide for Contractors to Share with Homeowners
April 12, 2010