24 Things You Need to Know About Insulation

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Seal the Rim Joists

Uninsulated rim joists are huge energy losers. Now’s the time to insulate and seal your rim joists. One option is to seal the rim joists with rigid insulation cut to fit. We recommend a minimum of two-inch-thick extruded polystyrene, but check your local codes to see what’s required. If you have a table saw, use it to cut strips equal to the depth of your joists. Then use a fine-tooth handsaw, utility knife or miter saw to cut the strips to length. Fill small gaps with caulk, and larger ones with expanding spray foam from a can.

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How to Find the Gaps

Before you crawl into your attic, make a rough sketch of the floor plan and the ceiling below the attic. Sketch in the walls, the chimney, the main plumbing stack, ceiling electrical fixtures and lower sections of ceiling. They all have high leak potential, and your sketch will help you find them when you’re in the attic.

To help generate actual leakage, place a box fan in a window so it blows air into the house. Then close all other windows and doors. Tape cardboard around the fan to eliminate large gaps. When you turn the fan on high, you’ll slightly pressurize the house, just like an inflated balloon. Then when you’re in the attic (with the attic door closed), you can confirm a leaky area by feeling the air coming through. You may even spot the insulation blowing in the breeze. Keep your house warm with these attic door insulation covers.

Another helpful sign is dirty insulation (photo above). Insulation fibers filter the household air as it passes, leaving a dirt stain that marks the leaky area.

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Use Foam or Caulk for Small Gaps

It’s best to keep your can of expanding foam and caulk gun handy and plug the obvious electrical cable holes and fixture boxes as you move around working on the bigger air leaks. Make sure you get to the plumbing vent, because the gap around it is usually large. Also look for the 2×4 top plates (framing) of interior walls and follow them, keeping a sharp eye out for electrical cable holes and dirty insulation, which would indicate a gap or long crack between drywall and a wood plate. Seal these with caulk.

Work carefully with expanding foam because it’s super sticky and almost impossible to get off your clothes and skin. Wear disposable gloves when working with it.