We just bought and moved into an older home in Castlegar. There is a fully finished basement with old linoleum tiles on the concrete floor throughout. We’d like to remove the tiles and replace them with vinyl flooring and carpet. Because we don’t know the history of this basement we’re concerned that the floor may get damp or wet in the spring. So we’re wondering if it would be a good precaution to construct a wood subfloor and then lay the new vinyl and carpet on it to ensure they will not be affected by dampness?

Like most things in life it is a bit of a gamble to know which course to take. But here are some factors you can consider before making your decision. Look carefully at the existing lino tiles, especially along the exterior basement walls that retain the highest levels of earth outside the concrete walls. Also check carefully in locations where the downspouts or rain gutters drain against the foundation walls. If the tiles are curled or lifting or the baseboards are water stained you can expect that your basement floor gets seasonally damp. You could expect that the same problems will occur with your new vinyl flooring (blistering and lifting) and carpeting that will possibly get damp and mouldy. In other words, if these signs are present, it would be reasonable to install a wood sub-floor to help keep your new flooring dry.

However, if your existing flooring and baseboards show no signs of moisture damage and there are no other signs of dampness like water stains or the smell of dampness, you could assume that this is a fairly accurate historical record of a dry basement. You may also take comfort in the fact that most areas of Castlegar are well-drained sandy soil because this area is a series sandy benches left behind as the Columbia River receded to its present location. These forgiving soil conditions help keep most Castlegar basements dry even when poor building details such as no gutters, downspouts and leaders on roof eaves aggravate and encourage damp and wet conditions in basements.

If you decide you can afford the additional expense of a wood sub-floor, or you need the sub-floor to protect your new flooring, here are some f actors to consider. First, you can save yourselves the work of removing the old lino tiles (which may contain encapsulated asbestos) because you can construct the wood sub-floor directly over your old lino tiles. You will also have an opportunity to re-seal your concrete slab from the potential hazards of radon gas. This can be done by installing a well-sealed 6 mil polyethylene membrane over the old tiles before you lay the wood “sleepers” and plywood sub-floor is installed.  Be sure to seal all the seams and penetrations in the polyethylene and caulk the edges of the plastic tight to the interior and exterior walls. The tighter the seal, the better protection you will gain from radon gas. The wood sub-floor will also be slightly warmer and more flexible to walk and sit on than the concrete floor in direct contact with the vinyl and carpet.

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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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