canned spray foam for helping with attic insulation installation prep
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The Number One Prep Step: Seal Air Leaks

Gaps in the attic or between the lower floors and the attic will let heated (or cooled) air escape to the great, unconditioned outdoors, making any insulation you add essentially useless. (Find a diagram of common air leaks here.) Here's a quick primer on fixing draft-prone spots.

1. Around attic windows: Use canned, minimally-expanding spray foam (DAPtex Plus Window & Door Foam Sealant, $5.44 for 16 ounces; sears.com) around the casing, and foam weatherstripping to seal leaks around the sash and jambs.
2. Around pipes, wires, exhaust fans, and ducts: Gaps of ¼ inch or less can be sealed with fire-blocking caulk (3M Fire Block Sealant, $6.57 for 10.1 ounces; homedepot.com); seal larger ones up to ½ inch with fire-blocking spray foam (Great Stuff Fireblock Insulating Foam Sealant, $9.84 for 16 ounces; amazon.com).
3. Around chimneys and flues: Use metal flashing sealed with high-temperature caulk (SUPERBOND Silicone Sealant, $7.90 for 13 ounces; grainger.com) or furnace cement (Oatey High Heat Furnace Cement, $12 per half gallon; lowes.com).
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