Better ways to insulate around doors, windows


By CCHRC Staff

The “Ask a Builder” series is dedicated to answering some of the many questions Fairbanks residents have about building, energy and the many other parts of home life.

Q: A lot of older homes use pink or yellow fiberglass insulation around doors or windows. If I’m going to reseal any of them, is there a better way to do it?

Fiberglass is a great insulator but still allows air to flow in and out. A can of minimal expanding spray foam will more effectively air seal your doors and windows.

Open the trim around the windows then push the fiberglass in slightly. Make sure the spray foam fills all the cracks for a tight seal. The goal is to make the area around doors and windows as airtight as possible.

Even low expanding foam will swell significantly. Painter’s masking tape can be used to protect finished surfaces from spillage and can be removed once the foam cures. As an alternative, a compressible foam backer rod and silicone caulking can also provide a good long-term seal in difficult spots — especially when if you are working in temperatures too cold to apply foam. Also moisture can affect the foam and it should not be applied to wet surfaces.

Q: When it comes to heat and energy expenses, why are walls such a big deal?

In looking at a home, people often think their roof is where they lose the most heat.

The walls, however, might be a bigger issue.

On a home, walls compose the greatest surface area exposed to the outside. This is important because the laws of thermodynamics teach us that heat will always move to cold whether it moves up, down or sideways. With an exterior wall, one side is always exposed to the cold so heat will naturally always try to move inside to outside through the wall. We tend to assume heat always rises, so our roof must be responsible for the greatest heat loss. What actually happens is that air rises when it is warmed and it becomes a vehicle for the transfer of heat. This does not mean there is any reduction in the amount of heat moving through walls. A home can easily have many times more heat loss through walls than through the roof.

There are many ways to reduce heat loss through walls. The simplest is to carefully caulk and air-seal any places where air can move from the interior or exterior, particularly around windows and doors. Re-insulating walls and adding additional insulation inside or outside can be done if proper techniques are incorporated.

Be sure to consult with or hire a professional before attempting this kind of weatherization.

Remember, a house is a system and what is done to one part of a house may affect overall performance of the home both positively and negatively.

Alaska HomeWise articles promote home awareness for the Cold Climate Housing Research Center (CCHRC). If you have a question, e-mail us at can also call the CCHRC at (907) 457-3454.