Cool air sinks, so the foundation walls are where cold air will try hardest to enter your home. This is what causes the basement to be the coldest part of most people’s homes. Make sure you only air seal and insulate around the walls, where cold outside air comes in, and not the basement ceiling.
There is a common misconception that the basement should be treated like the outdoors. The truth is, your basement is much more connected to inside than outside, and that’s a good thing, especially if you have a furnace, boiler, or water heater down there. They operate more efficiently when the air around them is a reasonable temperature.
A cost effective way to reduce airflow and lower your home’s energy usage is to air seal and insulate by creating barriers between cracks and openings in your basement walls. Adding insulation to these walls provides resistance to the flow of heat and provides moisture control.
Some of the most commonly used materials for air sealing are:
Caulk - Seals gaps of less than ½ inch. Select grade (interior, exterior, high temperature) based on application.
Two-Part Spray foam - Fills large cracks and small holes. It can be messy; consider new latex-based foams.
Weatherstripping - Used to seal moveable components, such as doors, windows, and attic accesses.
Rigid Foam Board - Used for insulating and sealing large openings-to be used in tandem with spray foam.
When it comes to insulation, foam is an effective way of sealing openings around windows and door brick framed windows. Air sealing and insulation are most effective when both are installed together.
Air sealing and insulation in basements can be complicated by the presence of combustion appliances that require sufficient ventilation for combustion and exhaust. Ideal ventilation allows for ample fresh air directed to the mechanical equipment intake and safe removal of combustion gases in the flue or chimney. Have a heating professional or energy auditor check that combustion appliances are operating safely and efficiently.
Seal and insulate leaks around doors and windows and the “bypasses” that leaks air through openings in the building’s interior into the attic or walls.
In most basements, especially basements where boilers, furnaces, or water heaters are located, insulation should only be installed on exterior walls, NOT on surfaces shared with conditioned spaces, such as the basement ceiling.
Air bypasses are often created during initial construction and cause not only heat loss, but also the potential for structural damage through moisture condensation, so should not be ignored.