Basement Insulation near you

Insulating the inside of a foundation makes the concrete colder and hides it behind a new wall, so water problems come first. NRCan suggests a simple check: tape a sheet of plastic about 1 m (40 in.) square to the wall and the slab, then look at it after a day or two. Condensation on the room side points to humid indoor air; moisture underneath shows dampness moving in from the ground and, NRCan adds, the possibility of radon entry. For leaks, drainage and grading, start with our basement waterproofing page.

Exterior insulation covers the outside of the foundation with rigid boards made for use below ground, protected where they rise above grade. NRCan notes that the outside surface tends to be more continuous and easier to insulate, and that keeping the foundation warm eliminates freeze–thaw stress and makes frost unlikely to reach the footings. It requires digging around the house, so it makes most sense when the foundation is being excavated anyway for waterproofing or new drainage.

Interior insulation is the usual choice in an existing home. NRCan points out that it can be folded into a plan to finish the basement and done at any time of year, one section at a time. The trade-off is a colder foundation and finishes that can hide moisture as it develops, which is why the materials against the concrete and a continuous air and vapour barrier matter so much.

Most interior assemblies pair a layer that can safely touch concrete with a framed wall for wiring and drywall. NRCan recommends medium- to high-density foam board with good moisture resistance, such as extruded polystyrene or Type IV expanded polystyrene, against the foundation, and describes closed-cell spray foam, applied only by a certified installer, as another high-quality option.

Floors come second. NRCan notes that most heat is lost through the upper part of the foundation walls, so basement slabs are seldom insulated. A bare slab still feels cold underfoot, though, and an insulated or separated floor makes a finished basement more pleasant, especially for bedrooms or a playroom.

Over an existing slab, the usual options are rigid insulation under a new subfloor, or subfloor panels designed to keep the finished floor off the concrete; both use up some headroom, so measure the ceiling height first. When a slab is replaced or the floor is lowered, insulation can go under the new concrete, and NRCan calls that an excellent opportunity to install in-floor heating or make the slab ready for it. It is also the moment to plan for a radon system under the slab.

Radon is a radioactive gas from the soil that enters through cracks, joints and gaps around pipes, and basements usually have the highest levels. Health Canada notes that sealing those openings can help but isn't a standalone way to lower radon, because every opening is hard to find and seal for good. It recommends a long-term test of at least three months, and its measurement guide calls for testing again after renovations that affect the structure or ventilation of the home. Start the test early, because results take months and mitigation is simpler before the finishes go on; our radon testing and mitigation page explains the next steps.

Insulating a bare basement wall is often simple, but it usually comes with plans to finish the space, and that brings in the building code. Most municipalities require a permit to finish a basement, especially when a bedroom or bathroom is added, and a basement bedroom needs an exterior door or a window large enough to escape through. Frame around any future egress window now rather than tearing out new insulation later; our basement renovations page covers the requirements. Ask the permit office whether it wants to inspect the insulation and the air and vapour barrier before the drywall goes up.