Moisture between vapor barrier and insulation in shed


We have just insulated our shed and put vapor barrier inside the insulation, with a layer of tar paper between the insulation and the siding. We are noticing that one wall is sweating and moisture is collecting between the insulation and vapor barrier. Berfore we drywall, we want to eliminate the moisture. The attic of the shed is vented, so I can not understand why we are seeing this moisture still? Does anyone have any advice as to how to fix this and why we would still be getting moisture? We would like to use the shed as an office and have also installed heating. Are we still lacking proper venting or is this likely because we have not properly sealed the vapor barrier? Thanks in advance for any help. If it makes a difference, we are in BC Canada, moist climate with a mix of cold and warm.
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incorrect. Since the installation can not be absolutely air tight, some moisture will find its way into the insulation and must have an easy escape path. In cold climates it is recommended that the vapor barrier should be on the warm inside and the outside be ventilated. You need to remove the tar paper.
Don Young
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Thanks for replying Don. Perhaps I used the wrong term, as the paper is not truly tar paper...but rather the black pourous paper recommended by the folks at Home Depot and appears to be what I see builders using ont he new homes. Is this the wrong paper? and if so, what should we have between the insulation and the exterior siding?
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tarpaper is vapor permeable and is not considered a vapor barrier. in fact, i believe tarpaper is more permeable than tyveck. I have yet to see a vented wall, and if they were, the R value loss to wind wash would be significant. is it possible that your wall got wet before you insulated it? If it's just a small amount of condensation, it should find its way out. otherwise, pull the vapor barrier off, and run an electric or sealed combustion heater to dry it out.
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Perhaps I should explain the layers we have installed...
We have the siding outside, with a layer of the black paper inside that, then the insulation inside that and finally the plastic vapor barrier on the inner most layer. We have dried the moisture and resealed the vapor barrier, but it is now wet again between the vapor barrier and the insulation.
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so how is the black paper installed? it should be installed shingle style, so that the water that gets through your siding is shed. is it possible that wind driven rain has entered the stud cavity?
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I did not install the black paper..the initial builder did, but it does appear shingled and attached directly to the outside of the studs. The moisture appears to be vapor and not coming in from driven rain(it has also been good weather recently). The wet wall also has a fence directly outside it that would block driven rain. Only the inside of the insulation is wet and the outside facing insulation, black paper and studs are as dry as a bone.
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The problem you describe can usually be attributed to having two vapor barriers. For example, a poly vapour barrier on the inside and a vapor resistant sheathing, such as OSB, on the outside.
However, since you state you "just insulated", it is likely there was moisture in the insulation to start with, and the moisture is condensing on the poly..
Recommend you slash the poly, let the insulation dry, then repair the poly using tuck tape and see if the problem re-occurs.
Since you don't have sheathing, another possibility (remote) is rain getting through the siding on the windward side and soaking the tarpaper to the point of moisture penetration.
Gary in Royston, BC
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Maybe that is the first real barrier runs into before trying to exit. Do you have a moisture barrier on the inside? Before the insulation?
tom @ www.Consolidated-Loans.info
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Yes, the moisture collects between the moistue barrier ad the insulation, inside facing. It is a cemet floor in a moist location.
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IMHO,
If that barrior that protects the insulation isn't stopping the moisture from penetrating through it, to the outside, I would install another barrier over the inside. Some say 4mil but 6 isn't much more and less likely to tear will installing.
Just a guess, since I can't see your setup.
tom @ www.Consolidated-Loans.info
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