Basement renovation: insulation best practices

In comparison to today’s standards, the basement insulation in homes built between the 1950s and 1980s was generally inadequate. The practice in those years of insulating using pieces of 1” white styrofoam or fibreglass batts (with a vapour barrier of questionable effectiveness) is known to create moisture problems that can, in turn, lead to air quality issues due to the development of mould.

You are surely familiar with the cool, dank environment that we all associate with basements in homes from a certain era. This is most often caused by inadequate insulation and the presence of moisture and/or mould trapped inside the walls. In practical terms, this type of insulation can increase your heating costs by as much as 20 to 25%!

Effective, durable insulation

Insulating a basement from the inside is certainly the most common, and most affordable, option. The following is the best approach to installing a basement wall system that guarantees long-lasting protection against both the cold and air filtration.

1. Check the foundation walls for cracks.

If you are getting ready to proceed with a basement renovation, keep in mind that this is the ideal time to gain access to the foundation walls. The first step is to remove all wall coverings and insulation and to check the foundation walls for cracks.

2. Determine whether you will be erecting new framing in the basement.

If you are not planning for new framing, it is critical that there be at least 1” of air space (see photo) between the foundation walls and the existing framing. This helps to prevent the formation of thermal bridges, which can lead to condensation and mould problems.

If you do remove the framing, spray urethane foam should be applied directly to the foundation walls. This creates a shell of continuous insulation without any thermal bridging as well as a continuous air and vapour barrier. The only drawback to this practice is that you lose a few square feet of floor area in your basement – around 15 sq. ft. in a basement measuring 1,000 sq. ft. in area.

If you redo the inside walls, you may decide to use wood or metal framing. Regardless, wood framing built from 2×3s requires temporary installation of metal furring to stabilize the 2×3s during application of the urethane. When using wood framing made of 2×4s, this temporary wood furring is not necessary. Do you prefer metal furring? In that case, you’ll need to install two temporary wood furrings to prevent the urethane from deforming the metal studs as it cures.

Advantages of metal studs: they are pre-drilled with access holes to make easy work of running electrical wires, and they don’t absorb any moisture in the event of water damage. Wood, on the other hand, readily absorbs water and moisture, and you have to drill a hole in each stud to run your wiring.

3. Install the electrical wiring.

If you are leaving your partitions intact, run electrical wires again where necessary, and then apply the urethane on top of the wiring (the National Building Code authorizes this method).

Electrical box: in accordance with current construction standards, a styrofoam block (rigid insulation) along with a plywood sheet should be installed behind the electrical panel.

4. Leave space between the plumbing and the foundation walls.

Are you planning on redoing some of the plumbing in your basement? If so, then be sure to leave at least 1” clearance between hot/cold water or waste pipes and the foundation walls. Then, insulate behind the pipes using spray urethane foam.

Plumbing vents and pipes: it is absolutely essential to use adequate insulation between foundation walls and plumbing pipes to keep the pipes from freezing. To ensure that indoor heat reaches all piping, take care also not to insulate the interior sides of pipes.