Insulating Your Basement Walls

  • 3-30 hours
  • Intermediate
  • 200-1,500

Traditional masonry basements, whether they're poured concrete, concrete blocks, or even stone, have very little insulating value. Uninsulated basement walls account for a substantial amount of heat loss. In some cases it's estimated up to 20% of the heat is lost when the basement walls are not insulated.

One can quickly see why adding insulation to the basement walls, whether or not they are finished, makes the basement warmer, and the floors above more comfortable, while saving money on heating costs. Read on for advice on insulating your basement walls.

Don't Rush It

unfinished basement

Although installing insulation on bare walls may seem like a pretty simple project, take some time to plan before you start insulating. Look for signs of structural damage like cracks or bulges in the wall. Also inspect for moisture problems such as leaks, dampness on the walls, efflorescence on the concrete, or blistering and bubbled paint.

Any structural damage or moisture issues need to be fixed before you insulate your basement; otherwise, you are just hiding a problem that will haunt you down the road.

While you're checking out your basement walls, note any existing features that will make your insulating job more difficult, and plan how to deal with them. Electrical panels, plumbing pipes, and built-in cupboards and shelves all require special planning.

Insulating Your Basement Walls

What you plan to do with your insulated basement will help determine the type of insulation you choose. The most common choices for basement insulation are fiberglass bats, poly foam board, and polyurethane spray foam insulation.

Unfinished Basements

unfinished basement

Spray foam makes an ideal choice for rock and rubble foundations; it has a high R-value. It expands to fill tiny nooks and cracks; however, it's best applied by a trained professional and commonly needs to be covered with a fireproof coating.

Rigid foam board is also a good choice for unfinished basements. It has a high R-value per inch. Since that means it's thin, it doesn't require much supporting structure; however, fire regulations commonly require foam boards be closed in with a fireproof covering like drywall, reducing their advantage over fiberglass bats in unfinished basements.

Finished Basements

finished basement space

Fiberglass bats make an excellent choice for finished basement walls. They're easy to handle, inexpensive, and readily available. The main drawback to fiberglass bats is that the fibers can loosen and float around, making them difficult to handle.

Always wear long sleeves, a hat, eye protection, gloves, and a dust mask when working with fiberglass insulation to keep the fibers off your skin and out of your lungs.

In a finished basement where the insulation will be covered with drywall foam boards save space over fiberglass; however, foam boards are more expensive than fiberglass bats, offsetting their space-saving benefits.

Before closing a finished basement wall, you must install a vapor barrier to prevent moisture transfer between the warm room and the cold insulation behind the wall. A vapor barrier can be achieved using faced fiberglass bats, or by covering the entire wall and the insulation with an unbroken sheet of plastic.