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  • Condensation in garage vapor barrier (south facing wall)

    Hi! I just insulated my garage with plans on drywall and heat of course.

    now, it’s been cold at night and very nice during the day this week and on the wall that has sun on it all afternoon I am getting condensation between the rockwool r22 batts and the 6mm vapor barrier. The outside of the house is vinyl siding, house wrap, osb plywood and then 2x6 studs.

    i used rockwool r22 2x6 batts with 16 centers. The condensation starts around mid afternoon after the sun has been on the wall for 2-3 hours, mostly disappears at night and is almost all gone by morning.

    having said all that, I am trying to think of other weather situations I could run into which would affect the garage in this way. I’m not worried about winter so much, mostly spring summer and fall.

    i am considering certainteed “smart” vapor barrier at this point. Does anyone have any other suggestions I could try out before I close up the walls?

    thanks in advance!!





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  • #2

    Re: Condensation in garage vapor barrier (south facing wall)

    Whats on the outside?

    Is it new construction or older?

    My advice is to take the vapour barrier off and let it actually dry out.
    Don't cover it up while its still wet inside.

    Nathan

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    • #3

      Re: Condensation in garage vapor barrier (south facing wall)

      It’s 10 years old

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      • #4

        Re: Condensation in garage vapor barrier (south facing wall)

        Since your wall was uncovered and you were paying attention, you likely saw what is happening in a lot of homes but is hidden by the wall covering. Have a look at something like "summertime solar diffusion".

        billh

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        • #5

          Re: Condensation in garage vapor barrier (south facing wall)

          I've always been told to not vapour barrier in something like a garage that isnt constantly heated as it could cause condensation. One thing the insulation guys pointed out to me is, even if you keep your shop heated consistently simply opening the shop door (we have big doors) lets in a blast of cold air which will cause condensation.

          That's what Ive always been told, would like to hear of a better solution if there is one.

          Just a thought... what if you got one of those DIY spray foam kits and just used it to seal the cavities? I bought one of those kits before, expensive at 200+ for 200sqft @ 1" thick. Should go quite far though just spraying along the seams of the osb and 2x6? My belief is your getting cool moist air coming through the siding and condensing against the warm vapour barrier?

          Wish I had the perfect answer for ya but I don't, good luck!

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          • #6

            Re: Condensation in garage vapor barrier (south facing wall)

            I suspect that the rock wool is not dry for one thing, and when the wall gets warm the inside of the garage is colder than the wall, so now the moisture is condensing on the colder surface.

            I don’t know what you have on the outside of the wall, something like tyvec or similar should let the moisture out and prevent it rom coming in, so as long as you have the moisture barrier on the inside you do prevent the moisture from inside entering the wall, the problem now is, how to get rid of what is in there already, and if this is enough to be a problem in the long run.

            Maybe there is not a real problem, and if you have inside cladding the temperature differences will be less, so less moisture on the vapour barrier inside the wall, all just in my opinion of course.
            Last edited by Leo Van Der Loo; 10-12-2019, 01:24 PM.

            Have fun and take care
            Leo Van Der Loo

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            • #7

              Re: Condensation in garage vapor barrier (south facing wall)

              Originally posted by Beaverfever1988 View Post
              I've always been told to not vapour barrier in something like a garage that isnt constantly heated as it could cause condensation. One thing the insulation guys pointed out to me is, even if you keep your shop heated consistently simply opening the shop door (we have big doors) lets in a blast of cold air which will cause condensation.
              I don't buy that. I've done lots of reading on insulation, vapor barriers and air sealing & have never seen that advice. What your insulation guy said makes no sense either. Where is that cold air going to cause condensation?

              My best guess for the OP's situation is that there was moisture in the wall before the VB went up. I'd take it down & put some fans in there to dry things out before closing it all in. It sounds like the outside is well dried in. Maybe the rock wool itself was damp?

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              • #8

                Re: Condensation in garage vapor barrier (south facing wall)

                Thanks for all the responses!

                I’ll take down the vapor barrier and let it dry out for a few days I guess. I’d really like to get my hands on some smart membrane and give that a shot but we will see.

                i wonder if using strapping on that wall and then vapor barrier would be helpful? That way there would be a little air space between the insulation and VB.
                nnieman likes this.

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                • #9

                  Re: Condensation in garage vapor barrier (south facing wall)

                  Originally posted by drzaius View Post
                  My best guess for the OP's situation is that there was moisture in the wall before the VB went up. I'd take it down & put some fans in there to dry things out before closing it all in. It sounds like the outside is well dried in. Maybe the rock wool itself was damp?
                  Thats my thinking as well but it’s impossible to say for sure.

                  Nathan

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                  • #10

                    Re: Condensation in garage vapor barrier (south facing wall)

                    Originally posted by Dropsix View Post
                    Thanks for all the responses!

                    I’ll take down the vapor barrier and let it dry out for a few days I guess. I’d really like to get my hands on some smart membrane and give that a shot but we will see.

                    i wonder if using strapping on that wall and then vapor barrier would be helpful? That way there would be a little air space between the insulation and VB.
                    If you put wood strapping between insulation and drywall it will mould - if there is a moisture issue.

                    If you can’t find the source of the moisture issue then my advice would be to leave the vapour barrier off.
                    There has been an awful lot of houses build without vapour barrier ....

                    Nathan

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                    • #11

                      Re: Condensation in garage vapor barrier (south facing wall)

                      As soon as you paint the wall you are starting to add a vapour barrier although not a real great one with the first coat.
                      billh

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                      • #12

                        Re: Condensation in garage vapor barrier (south facing wall)

                        After you get the VB down take a peek behind the insulation. the moisture has to be coming from somewhere now would be the time to find the source, before you do anything else.
                        nnieman likes this.
                        Jerome
                        Canada's South Coast

                        Port Colborne On.
                        Every loaf of bread is a tragic tale of grains that could've become beer.......but didn't....

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                        • #13

                          Re: Condensation in garage vapor barrier (south facing wall)

                          Thing is the garage has been without insulation for 7 years and there are zero signs of moisture anywhere on that wall.

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                          • #14

                            Re: Condensation in garage vapor barrier (south facing wall)

                            How long was the insulation up before the VB went on?
                            How cold has it been before the VB went on?
                            What were you using to heat the space?

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                            • #15

                              Re: Condensation in garage vapor barrier (south facing wall)

                              Originally posted by drzaius View Post
                              How long was the insulation up before the VB went on?
                              How cold has it been before the VB went on?
                              What were you using to heat the space?
                              Insulation was up one day maybe before the VB went on. It hasn’t been cold during the day. Maybe goes down to 1-5 C at night and then highs of 15-20 C last week.

                              wasn’t using anything to heat the space because the heater isn’t installed yet. That’s why the garage stayed cold all day while the hot afternoon sun was beating on the one wall.

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