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lolmeansilaughed t1_iybonum wrote

Reply to comment by preferablyprefab in Plan to frame part of basement and have a few questions by Ad-Nauseam91

Do you have any links as to the correct vapor barrier for each climate zone in the US? Like OP, I've never been able to find good info on that either.

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preferablyprefab t1_iye5x74 wrote

No, it’s not really prescriptive. There are so many variables of construction methods and materials, heating and cooling systems, and how they interact.

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lolmeansilaughed t1_iyet79d wrote

Thanks, I figured as much.

My house is in Maryland where we get all four seasons, with a walkout-style foundation and a natural stone facade, built in the early 60s. I did some remodeling and got inside some walls above and below grade and found no vapor barrier. At the time I couldn't find good info so just assumed it was built correctly, and the vapor barrier was either part of the exterior or was not needed. Homes under construction around here you always see with Tyvek Homewrap before the siding goes on, which is assume is a vapor barrier.

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preferablyprefab t1_iyf2bja wrote

Tyvek is a water resistant barrier - its purpose is to reduce wetting behind your siding (whatever it is) and it is slightly vapour open to allow moisture to escape if the wall assembly does get wet. Think of it a bit like gore-tex; water doesn’t get in but some vapour can get out. Buildings are ok getting a bit wet - it’s generally only bad if they can’t dry out.

Tyvek can also perform as an air barrier if detailed correctly but that’s not what you’re seeing on most residential construction.

Older buildings don’t usually have a vapour barrier and it’s not an issue because they are also poorly insulated and draughty. So they tend to dry out.

In a better insulated house that’s relatively air tight, problems occur where warm air meets a colder surface and you get condensation. Could be warm outside air meeting cold interior surface if you have AC. Could be warm interior air meeting cold exterior surface if you have heat blasting on cold days. If that condensed moisture gets trapped and won’t dry out, you get rot.

So - your 60 year old house that’s rot free is probably fine, but may be an energy pig. If you update it with better insulation and make it air tight to lower energy costs, that’s when you need some advice to get the details right.

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