We’re planning a basement renovation that will include insulating the bare cement foundation walls. I’ve asked several people who have done this about where the vapour barrier should be located and I get different advice every time. I know if I install it in the wrong location it will cause problems, so can you explain what's best?

There is a lot of confusion around this subject because there have been mixed messages from building inspectors, building technologists, and Code experts on this topic. Part of the confusion stems from different climactic conditions in a variety of regions across North America. In other words, the right location for a vapour barrier on a foundation wall in a dry climate may be quite different from its location in a wet, humid or moderately damp climate.

Here is the most recent school of thought of the subject for our Kootenay climatic conditions. If your non-structural wood framing (used to support the Fiberglas insulation) is touching and tight to the exterior concrete walls, then you should install a vapour barrier between the wood framing and the concrete. The reason for this vapour barrier is simply to protect the wood framing against possible rot damage from moisture contained in the concrete walls. Then you should install a second vapour barrier on the warm side of the insulation before you install your drywall or paneling.

If you hold your non-structural wood framing ½ inch or more away from the concrete wall(s), you do not need the first vapour barrier between the concrete and the wood-framing members. However, don’t expect that this will be the last word from the experts on this subject. Building technologists are always revising these strategies in attempts to control and eliminate dampness and mould inside wall cavities in basements. Another alternative to consider is installation of high-density R12 Styrofoam insulation caulked directly to the foundation concrete. Your concrete will have to be fairly straight and flat to use this strategy. Then you can seal all the seams with caulking and caulk the drywall directly to the Styrofoam, eliminating the need for non-structural wood framing.

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This article was written by Steven Cannon, a Registered Building Official and partner in Lynch Building Inspection Services Ltd. of Nelson, British Columbia. It originally appeared in The Nelson Express.

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