Our house is just about complete, at the trim and flooring stage. We have just noticed dampness/water coming from a couple of garage receptacles that are on the house side wall. Assuming it was a plumbing leak I cut a section of drywall out. We have a 2x6 wall with R20 insulation, then a 3/4" foil clad insulation (R5) on the outside wall and then the garage side drywall.
When I cut a section out from the garage side I found it wasn't a plumbing problem and that the foil side of the 3/4" insulation (nearest the house) had droplets running down it. I tried a couple of locations and found the same thing.
The builder is saying it's because the heating is on in the house and it's only natural with it being so cold outside. I countered that there may be a slight temperatutre difference but the vapour barrier should prevent moisture getting out but he wasn't convinced.
I'm concerned that we will get rot and have some serious damage if this happens every winter.
Does anyone have any idea why this is happening?
Should I be as concerned as I am or is it part of the drying out process as the builder believes?
I assume it's vapour leakage but how do we/the builder determine where it is leaking?
Your help will be much appreciated.
Phil

Have your interior walls been painted yet. Was the batt insulation installed with a kraft face on the interior.

Clearly what's happening is the foil face on the board is acting a vapor barrier. The moist air from inside is entering the wall and condensing on the cooler foil surface. If you have enough moisture that it's seeping from the outlets you've got a problem and don't let the builder tell you otherwise.

Moist air will permeate the interior wall it has to dry somewhere - generally to the exterior through a semi permeable surface. That much moisture in a wall is going to mold and it won't take long to happen. Like this summer as soon as that garage heats up. I can't believe a building inspector will let this pass.

You don't show where your located? That would help.

There should not be vapor leakage on the inside of the foil where the glass insul is.
The vapor Barrier "foil" HAS to be on warm side of the house even if there is a garage there.
From inside the house to garage.
Drywall
vapor barrier
glass insul
drywall on garage side.

If this is revered then its not right. 5% of moisture in insulation causes it to loose 95% of its insul value.
garage there or not.


Signed 21 Boat

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Thanks Rivethead, I think you understand the problem. The information you requested - Interior walls have been painted. Don't know what a Kraft face is - we have from inside out - 1/2" drywall, 6 mil vapour barrier, R20 batt insulation, foil backed foam board and then 5/8" drywall. We are near Toronto.
I can see thata some heat will escape but how is the moisture getting past the barrier?

For the moment you may want to digest this information:

RR-0410: Vapor Barriers and Wall Design —


And this Insulation Fact Sheet:

http://www.ornl.gov/sci/roofs+walls/facts/index.htm

Thanks again Rivethead. I did my homework as you suggested and read the 2 documents. It would appear that the construction is correct as per the examples and that some moisture escaping is to be expected. Because we have 6 mil plastic on the inside and the aluminum foil backed board on the outside it seems we moisture trapped between them.
The builder removed another section of drywall in the garage and found the same thing. The foil and the insulation touching it are wet to the touch. How moisture is getting past the 6 mil plastic which has been sealed with caulking top and bottom and at each join I still don't understand.
The studs are already discoloured in places because of the moisture and as you suggested previously, when the weather warms up we may get mold growing.
So the question now is "is this normal" and we only noticed it because the temp increased or is this excessive. Do we have a problem or have we just noticed something that happens in all houses?
If we do have a problem what can/should we do about it?
Thank you for helping.
Phil

The use of interior plastic does seem correct - but in your climate only (Builders Guide to Cold Climates by Joseph Lstiburek). I would not use it here. And they caution about it's use even in your area.

Any wall will leak some moisture even one with plastic. Typical for a near perfect seal is about a third of a quart per sheet of drywall per heating season. Not a problem if it has a chance to move somewhere. However a one inch open square will transfer about 30 quarts per sheet per heating season.

Outlets - switch boxes? But I don't think that's your problem right now.

To give your contractor a small break a new house is moist - especially given the time of year your building. Materials are damp including the studs - the drywall the sub flooring as well as the drywall mud and all the paint moisture. Then there's the concrete pouring out moisture also. That's why it is so important for the contractor to choose material that is dry as possible and do everything possible to keep it that way.

Typically it will take a house (done correctly) at least a year to come down to an ideal moisture level. 21Boat's post above tells you what is happening with your insulation.

You read the material - a wall has to be able to breathe to rid itself of moisture. Homes have to be built differently in different regions to handle that.

I've been reading for months about this issue in preparation to build a house in a year or so. So, forgive the long post.

Long and short of my opinion is that your contractor has created a double vapor barrier that is going to cause you a world of problems. If you were going to add the foam board on the outside - it should have been a semi-permeable board - or just the drywall or Homasote or Advantech with the drywall over that. Not foam lined with plastic or foil. Your set up is "never" going to allow the wall to dry out and the insulation will be damp and ineffective. You said you already see staining on the studs - the house isn't even occupied yet. Think about what that will look like in a couple years after that garage heats up in the summer.

Come back and keep the discussion going please. Sorry to be so negative when you should be excited about your brand new home.

Lets talk about your basement insulation at some point also - I can really get on a soapbox about that topic. In the meantime - do not allow them to put fiberglass insulation in direct contact with your basement masonry walls.

Rivethead I agree with your diagnosis. I think we have a double vapor barrier too but that seems to be the way houses are built around here. We are in zone 5/6 and the "Vapor barrier and wall design report" say that foiled back sheathing is OK. Seems to me if it is perfectly dry the foil will reflect the heat but it stops moisture escaping. At this time of year the foil is likely below the freezing point so any moisture freezes when it hits it and then melts when the weather improves.
The report doesn't in most examples show any vapor barrier on the inside so you would think that in their tests they would have experienced more moisture at the foil than we are getting - I don't understand. They talk about "sufficiently warmed" exterior barrier, does that infer that the temp at the foil shouldn't get lower than freezing point?
I believe it will improve as the house dries out but what damage is it doing in the mean time.
I hope to have the building inspector come around tomorrow and help us, I'll let you know what he has to say.
As for the basement, I hope we are OK, we have Tyvek all around trhe walls, then a 2" gap, then 2x4 wall with insulation in it and then 6 mil plastic.
Thanks again.
I'll be in touch