Keep Your Mould to Yourself

In my TARION-registered builder hat, I was recently asked this question:

"In the process of finishing my basement a little at a time as the money tree grows new leaves. What's the best way to do it?"

I could give you the stock answer--dampproof the interior foundation wall, build a stud wall, add fibreglass batts and a vapour barrier as per the Ontario Building Code, and most other Building Codes.

But the fact is that Building Codes are woefully behind
building science research into the best ways to ensure healthy, energy efficient basement living space.

In a cold climate, the best retrofit basement insulation system in a recent house is
to fix board-type insulation rated at least RSI18 against the walls, eg., Styrofoam SM, with either the appropriate adhesive or concrete fasteners and fender washers, seal the joints with air-barrier tape (red and very sticky); then in the spaces between the joists at the top, cut to fit foil-faced isocyanurate board, caulk and seal the joints with metal tape.

Next, build a stud wall, preferably of light gauge steel, add batts if you want to superinsulate or just drywall without a vapour barrier. (This is the way I did our custom home last year--though unfortunately, the inspector insisted on the vapour barrier.) And it's the way I intend to finish a custom home I am doing for a client starting next January.


Styrofoam insulation in Basement Wall attached with furring strips
photo: Dow Corp.

A cheaper way of finishing the walls would be to fix furring strips to the foundation wall through the insulation and use these to affix the wallboard. But this precludes electrical receptacles etc. on your exterior walls.

Whatever way you choose, be sure to provide dehumidfication during the summer months.