I am renovating the upper floor of a 1.5-story house that is just over 30 years old. It is reasonably well insulated, but there has never been a vapor barrier on the upper floor. Now that I have installed a vapor barrier, I wonder why it is so extremely important not to have any screw holes in it. If no moisture damage occurred in 30 years without a vapor barrier, why would a tiny screw hole be critical? To be safe, I tape over all the screw holes that have occurred during construction, but I am curious as to why this is so important?
Veronica
Veronica
If it were so important, it would have been a known problem in all houses from the 80s onwards. The fact that there are holes when you, for example, screw up panels doesn't matter since the plastic is clamped between the panel and the joist. Single holes for hanging things also do not matter. Especially if you have some form of forced ventilation that creates constant negative pressure in the house.
Before you renovated your house, there was nothing preventing moisture from escaping through the wall. Which it did everywhere. Since it happened across the entire surface of the exterior wall, there was never a large concentration of moisture trying to escape in the same spot.
Now that you have sealed your house, which is good, every hole in the sealing layer becomes a potential problem. Say you have a completely sealed house except for a hole the size of a Swedish five-krona coin. Then the moisture in the house will want to escape there and then condense in the outer wall. Then you've created a problem for yourself.
Seal away. The tighter, the better! Less heat will leak out as well
Now that you have sealed your house, which is good, every hole in the sealing layer becomes a potential problem. Say you have a completely sealed house except for a hole the size of a Swedish five-krona coin. Then the moisture in the house will want to escape there and then condense in the outer wall. Then you've created a problem for yourself.
Seal away. The tighter, the better! Less heat will leak out as well
Super - thanks for the response. There seem to be different opinions on the risks, but now I understand that the downside of leaks is that all moisture should exit at the same place. I'll check the ventilation too, so the house should stand for another 30 years...
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· Etelä Pohjanmaa
· 2 467 posts
If one understands the principle of a vapor barrier, one also understands that it should function together with a negative pressure (exhaust fan) in the house. Then a few screw holes make no difference whatsoever.