Basement walls are the ‘lead water pipe’ of 21st century
Once upon a time, homebuilders installed water supply pipes made entirely of lead, completely oblivious to the health dangers we now see so clearly.
“We’ve always done it this way”, a plumber from a century or two ago might have said. “So it can’t be bad.”
In fact, even the professional title “plumber” comes from the Latin word for the metal lead — “plumbum.” And while homebuilders of yesteryear were completely ignorant of the health-harming features they built into homes, is it possible we’re doing the same kind of thing now? I think so, and it’s found in basements.
Basements were almost never finished in Canada until after the Second World War, and even then finishing techniques began as primitive and evolved from there. We’re still evolving, though not fast enough in one area.
One of the big mistakes that settled into common use was the practice of finishing exterior basement walls in a similar way to above-ground walls, using wood studs with fibre insulation stuffed between them. This still happens regularly and I call this a mistake for two reasons.
The first is that moisture, temperature, and energy conditions around a masonry wall with soil on one side is entirely different from a wood frame wall built above ground. The second reason it’s a mistake is the way the difference in these conditions leads to mould and mildew growth that’s far too common in finished basements. Whenever you smell a musty basement, it’s not just a bad odour, it’s also a sign of health-impacting indoor air quality from hidden things growing behind the scenes, most often in walls. The question is, how can we do better?
The first step is to get rid of the old lead water pipe mentality that illogically maintains that doing something for a long time means it’s good. That’s simply not true. The next step is to examine the challenge of insulating and finishing exterior basement walls with fresh eyes, and not merely transplant existing notions to this unique application. This means using new materials in ways that always keep the threat of mould growth in mind.
Mould needs two things to grow: organic matter to feed on, and sufficient moisture to enable growth. The ideal way to finish exterior basement walls recognizes both these conditions as crucial and works hard to deal with them as part of responsible design. This is where modern foam insulations come in.
Many types of foam offer excellent energy performance and mould resistance for two reasons.
Foam is not a favourite food of mould and mildew, and the right kind of foam for basement use is also impervious to the passage of moisture vapour. Neither of these things are true about fibre-based insulations, and this is why I always recommend against using them in exterior basement walls. If internal wall cavity humidity rises high enough to trigger mould growth, it’s like having wet beach towels stuffed in the wall cavities of your basement. Who wants that?
Foam can be used responsibly in different ways for basement wall insulation. It can be applied directly over masonry walls with mould-proof drywall applied on top, it can be sprayed in the cavities of metal stud wall frames, or foam is used as the basis of rigid basement panels that never even touch masonry foundation walls at all.
As logical as all this sounds, let me warn you about something. The construction industry is slow to change, and you’ll run into many authoritative voices who’ll make the case for finishing basements “the way we’ve always done it”, using lead pipe logic. But the stakes are high, not just financially, but in terms of your health.
There’s a lot more to this topic than I have room for here, but you can learn lots more on my website at baileylineroad.com/ basement-insulation-preventsmold.
Visit Steve Maxwell online at BaileyLineRoad.com.