Fundamentals of Air Sealing

[Home Energy Saver]

Now you know why you need to improve the airtightness of your home, something about how air operates, and how to have your home’s airtightness measured. It’s time to put this knowledge into action. Let’s start with these three simple rules for air sealing when you remodel your home:

• Find and seal the big holes first.
• Find and seal the medium-sized holes second.
• Find and seal as many of the small holes as you can.

The size and nature of the hole determines the type of sealing material to use:

• For doors, windows, and access holes: Use weather strip, gaskets, thresholds, and door sweeps to reduce air leakage when the unit is closed.
• For big holes: Use rigid materials such as plywood, oriented strand board (OSB), drywall, foam board, or sheet metal to fill the hole; then seal edges with caulk or sprayed foam.
• For medium gaps and cracks: Fill the gap with backer rod and cover with caulk, or use a sprayed foam that will expand to fill the space. Caution: Use low-expanding sprayed foam around windows and doors. If you don’t, you may warp the frame, prevent windows from opening, and void the warranty.
• For small gaps and cracks: Caulk and sprayed foam work best.

The Airtight-Drywall Approach

Generally, the outer surface of your house should be your primary air barrier, because you don’t want unconditioned air getting into your building assemblies. But sometimes you don’t want interior air getting into your building assemblies, either. For example, in a cold climate, warm, humid air leaking into the wall cavities can condense when it hits cold sheathing, encouraging mold growth.

The airtight-drywall approach seals the interior side of the exterior walls, focusing on the top and bottom of each wall, around all the windows and doors, and wherever there’s a penetration through the drywall (at electrical outlets, switches, and light fixtures). By air sealing both sides of the exterior walls, you reduce the total amount of air leakage and reduce the possibility of moisture problems inside the walls.

Learning to See the Air Barrier

When designing a remodel, some architects use a simple trick to verify the continuity of the air barrier: On a plan or section, they should be able to trace the air barrier around the entire house without lifting their pencil from the paper. Any gaps where they jump from air barrier material to non-air-barrier material are design flaws that need to be addressed. Do your best to bring ducts inside the building envelope.