Whether or not your basement is a living space, it is important to air seal and insulate any leaks that might let in outside air and cool your home in the winter. A complimentary home energy assessment will review opportunities for your basement to contribute to your home’s overall energy efficiency. Home energy professionals will provide you with energy-saving products to install yourself, recommend additional upgrades, and coordinate air sealing and insulation services with weatherization contractors if needed.

Blower door tests are not included with a typical home energy assessment, but it may be worth the $300 – $600 cost to identify additional opportunities for weatherization.

Air sealing

Ensuring there are as few gaps as possible for indoor hot air to escape and cold outdoor air to get in reduces the heating load in a home. Air leakage can represent up to 40% of space-conditioning costs in a leaky building. Air sealing often involves re-sealing windows, replacing broken or jammed vents, and replacing the rubber seals around door frames.

Some areas that a home energy professional will focus on for improvement are:

  • If your basement is unfinished, the rim joists (the area between the top of the foundation and the floor above) can be sealed and insulated.
  • If you have electrical and plumbing penetrations in the basement, they can be sealed with foam or caulk.
  • If the basement has a bulkhead or walk-out door, weather stripping can be added to reduce air leaks.
  • If the basement has windows, they can be sealed around the perimeter. You may also want to upgrade your basement windows altogether, especially if they are single-pane.


Adding insulation slows heat transfer through the building envelope (walls, roof, floors, etc.); heat transfer is the leading cause of heat loss in the winter. Working with a professional contractor to improve floor and wall insulation can considerably lower heat transfer, improving your home’s efficiency. Many insulation contractors are trained to air-seal before insulating, when it’s much easier to do.

If the basement is unheated and you don’t plan to use it as a living space, consider either isolating the basement from the rest of the home by adding insulation between the floor joists, or improving the insulation of your basement walls with spray foam insulation. Talk to your home energy assessor about which approach is right for you, although be aware that Mass Save® may not offer incentives for either approach.

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