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I agree on low humidity being bad, but your remark on insulation does not seem correct. I'm only familiar with cold climates, so perhaps I'm overlooking somethi
by olau 4y ago
I agree on low humidity being bad, but your remark on insulation does not seem correct. I'm only familiar with cold climates, so perhaps I'm overlooking something, but mold needs moisture to grow, so it will appear where water condenses out of warm air on a cold surface. You can typically see this in windows.
So you need to prevent cold surfaces. The best way to do that is improving the insulation. The reason you can see water drops in the windows is precisely because they are inadequately insulated (e.g. only double paned).
Now, it's true that if you make an airtight home, then you need some kind of air exchange. And if it's really cold outside, then even if it's wet, once that air is warmed up, it ends up at a low relative humidity. In that case you need a humidifier. I guess depending on the outside air, you'd probably need both to stay in a comfortable range.
- paiute 4y agoIt's not super intuitive at first, but its cold climates were this is actually a big issue. Water vapor "wants" to equalize from a more humid to less humid environment. So when it's cold out - the humidity can drop rather low. Then you take a shower and create water vapor - which flows into the walls, through the insulation, and condenses against the colder exterior. Open a wall in any stick frame house in the rocky mountain region and mildew will be present. I am building a highly insulated house in a cold climate area and have blasted all the wood with copious amount of a silver based coating to inhibit mold growth.
- paiute 4y agoThis installation chart is a pretty useful starting place, regrettably local codes often require you to do the wrong thing https://www.certainteed.com/insulation/resources/do-i-need-vapor-barrier https://www.certainteed.com/insulation/resources/do-i-need-v...
- hedgehog 4y agoHave you investigated a combination of additional vapor permeable exterior insulation and impermeable primer for the interior walls? You may be able to minimize the amount of moisture staying in the walls and still hit your thermal goals.
- olau 4y agoAh, I see where you are coming from. The standard solution (for > 25 years) where I live is that you install a vapor barrier (plastic) to prevent the moisture from diffusing outwards. It needs to be on the interior side of the insulation in a cold climate. Edit: Sorry, I can see that you're aware of these. Perhaps my point is just that all standard houses where I live in cold climate uses vapor barriers. Moisture control is part of the building code. Trying to solve the problem with overly dry air does not make sense to me - the whole point of a house is making a comfortable living space.