Air Sealing Materials
Effective air sealing requires selecting the right material for each application. Caulk is used for sealing cracks and gaps up to 1/4 inch wide in stationary building components. Acrylic latex caulk works for interior applications while silicone or polyurethane caulk is needed for exterior and high-moisture areas. Spray foam in cans works for larger gaps up to 1 inch wide, with low-expansion foam recommended for window and door frames to prevent binding.
Weatherstripping seals gaps around operable windows and doors. Common types include adhesive foam tape for uneven gaps, V-strip for side jambs, and door sweeps for the bottom of doors. The choice depends on the gap size, expected movement, and exposure to weather. Quality weatherstripping should maintain its seal through seasonal temperature changes and door operation.
Priority Sealing Locations
The attic is the most important area for air sealing because warm air rises and escapes through the highest points in the building. All penetrations through the attic floor must be sealed, including plumbing vents, electrical wiring, recessed lights, duct boots, and chimney chases. The attic hatch or pull-down stairs should be weatherstripped and insulated with a rigid foam cover box. blower door test procedures. weatherstripping techniques. cellulose insulation.
The basement and crawlspace are the second priority because stack effect draws air in at the lowest level. Rim joists where the foundation meets the wood framing should be sealed with rigid foam insulation and spray foam. Sill plate gaps between the foundation and mudsill should be sealed. Duct penetrations through floors and walls should be sealed with mastic or foil tape.
Testing and Verification
After completing air sealing work, a follow-up blower door test verifies the improvement. The target for existing homes is typically a 20 to 30 percent reduction in air leakage. For new construction, the aim is to meet or exceed the energy code requirement of 3 to 5 air changes per hour at 50 pascals depending on climate zone.
Smoke pencils and infrared cameras help identify remaining leaks after initial sealing work. The combination of these tools with blower door testing provides a systematic approach to achieving a tight building envelope. Proper air sealing must be balanced with mechanical ventilation to ensure adequate indoor air quality.