Structural Air Sealing for Hot-Dry and Mixed-Dry Climates

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Best Practice: Use either interior gypsum board, exterior sheathing, or both as a continuous air flow retarder. Exterior stucco may also serve as an air flow retarder. Carefully seal big and little holes. Pay particular attention to sealing shared walls and attic spaces between garages and houses. 

Best Practice: Use sheet goods, such as hard board, rigid foam insulation, polyethylene sheet plastic, plywood, or sheet metal to seal holes behind tubs, shower stalls, stairs fireplaces, and other potential bypasses.

A tight building envelope is necessary to control the movement of air in and out of building assemblies. Air infiltration can contribute to problems with moisture, noise, dust, and the entry of pollutants, insects, and rodents. Using mechanical ventilation as a superior approach to supplying fresh air is discussed in the section on Mechanicals, Electrical, and Plumbing.

Moisture-laden air moving into wall or roof assemblies may lead to condensation and result in deterioration of moisture sensitive materials. Airflow retarders can be installed on the interior or the exterior side of the envelope or on both sides. Insulation made up of batt or loose fill products does not seal against air leakage. Rigid foam board insulation can be used as both a moisture and air retarder.

Controlling air movement through the building envelope requires sealing both the “big” holes and the “little” holes. The big holes occur behind bathtubs and showers on exterior walls, behind fireplaces, and where soffits or utility walls (double wall with chase) meet exterior walls or ceilings. Recessed lights collectively can be a really big hole in the ceiling assembly. These big holes are responsible for wasted energy (high utility bills) and condensation that can cause mold and wood decay. These holes are easy to seal during the framing stage but only when someone has the responsibility for making sure it gets done. Only airtight recessed lights (ICAT-rated) should be used in ceilings leading to unconditioned spaces.

The little holes occur between framing members (such as band joist to sill plate), around electrical boxes, and where plumbing or wiring penetrate the envelope. All penetrations leading to unconditioned spaces should be sealed with foam or caulk. See the Trades chapter, Building Tips on air sealants and the instructions for plumbers, electricians, and framers. Also see the sections later in this chapter for plumbing and electrical.

When air sealing drywall, gypsum board acts as an interior air flow retarder. The gypsum board is sealed to the framing members at the perimeter of exterior walls and around penetrations such as doors, windows, and attic hatches. The gypsum board is also sealed to electrical boxes on exterior walls. Air cannot move through the gypsum board and the taped corners.

There are many approaches and practices to sealing buildings. Many details and photographs of air sealing techniques can be found on the Building Science Corporation Web site at www.buildingscience.com/housesthatwork/airsealing.htm, in the EEBA Builders Guides, and in the DOE Technology Fact Sheet on Air Sealing available on the Web at www.eere.energy.gov/buildings/ documents/pdfs/26448.pdf.

Best Practice: One area to pay attention to for sealing is the intersection of the walls and roof. This area may involve an attic, cathedral ceiling, knee walls, all of the above, or other examples of complex roof lines. Tight sealing of this intersection may require blown-in foam. Careful work in these areas will help avoid ice dams.

Best Practice: Another area needing special attention for occupant health and safety is sealing shared walls and ceilings between attached garages and living spaces. Carefully seal any penetrations, block air pathways through the attic, and weatherstrip any doors.

For more information, please visit Building America or download the full reports below:

Cold and Very Cold Climates

Hot-Dry and Mixed-Dry Climates

Hot and Humid Climates

Marine Climates

Mixed-Humid Climates