Any documented condensation issues due to poly inside and tyvek outside?
mikeolder
| Posted in General Questions on
Hey everyone. When I resided my home with vinyl, I installed and taped typar before, and then later realized I had poly under my drywall inside. Uh oh!
I was wondering if there are any documented condensation failures (mold rot) due to poly inside and tyvek outside? Or are typar and tyvek permeable enough to keep the wall dry even with poly inside?
Thanks!
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Replies
I'll leave the experts to answer this properly, but you'll want to let people know where you live.
By the way, where I live, Ontario, Canada, this is standard practice.
Mike,
You are fine. As Eric noted, the stack-up y0u have is used on the vast majority of houses here in Canada with no problems associated with it.
House wraps are designed to allow drying to the outside. Interior poly is typically only problem in climates with a lot of air-conditioning.
Thanks Malcolm. Zone 5 Iowa. Many of us Iowans run AC for months on end. All the corn makes it super humid and unbearable.
Folks I know say its still a acceptable wall stack up, and I disagreed and was looking for proof but maybe I'm reaching. I'm sure it helps the air seal, but as long as its not to much.
Not that I would have removed my siding and typar. But when I see my dual pane windows and storms fog up in the summer mornings, I do wonder how moist the inside of my 4" walls are and how long until they dry with my board and batten siding..
So I'm gathering this is a totally acceptable stack up, as long as one side has a minimum permeability? Is there a article about combining retarders and barriers vs only one outside barrier?
Mike,
Maybe I framed the issue badly. The house-wrap is fine as a part of almost any wall assembly I can think of. What could prove to be a problem is the interior poly. During most of the year It stops moisture from entering the wall, while the house-wrap lets the wall dry to the outside. However, in the summer when you are using AC, the poly can get cold enough that the air in the wall can condense on it. That's got nothing to do with you having added house-wrap, it's entirely due to the presence of an interior poly air/vapour barrier.
Malcolm, do you ever work with exterior rigid foam out your way? If so, have you had issues with poly in those situations? I know Canadian code requires the poly. My brother in law is a builder outside Toronto and tends to use a lot of spray foam, but I’ve been trying to push him towards rigid foam, I’m just wondering if the code-mandated poly has been found to be an issue in that case.
Bill
Bill,
I've only used exterior foam on one small job, and as the only insulation, so the issue didn't c0me up. In our mild climate improving the wall beyond the standard 2"x6" with batts isn't the first improvement that makes sense.
While it is common practice up here, it's a misunderstanding that Canadian building codes mandate poly. They do require a vapour-barrier, but allow a variety of materials to be used, and its location is to a degree flexible. It's really habit that keeps builders using poly.
Houses with an inch of exterior foam and interior poly are very common in Quebec and Ontario. The anticipated problems with them haven't turned up. As long as the poly is well detailed, the walls seem to dry at a rate sufficient to stay safe.
Thanks Malcolm. The poly detailing I’ve seen in the houses I’ve been in outside Toronto has been pretty good. Some of the PEX installs not so much, although I did see the biggest drain water heat recovery setups I’ve ever seen.
I can see issues with mandating one type of wall construction in a province like Ontario that goes from an area of regular summer/winter seasonal wether up into a region of basically polar climate. I’ll have to look into that code detail some more.
Bill
I don't know if Ontario has different requirements for different parts of the province. BC is really good that way. We have separate building envelope requirements for coastal areas, and different R-values for all assemblies based on climate zones.