Will vapour barrier paint fix a flat roof with open cell insulation?
We are in Ontario and have been having problems with condesation and leaks from our flat roof for a few years, even after having the roof replaced. We finally determined that the problem is the original builder used open-cell spray foam to insulate instead of closed-cell. My understanding is that means we have effectively had no vapour barrier for the roof. The roof was designed as a cold-deck roof, so this needs to be fixed.
When we had the roof replaced, no one realized the existing insulation was open-cell because that is against the building-code and "no one would be that stupid." Well, original builder is long-gone and was that stupid, so now we need to fix it. Removing the roof and old insulation is one option. Removing all the internal drywall and old insulation is another. One suggestion was to use a paint on vapour barrier on the existing drywall. Does that sound plausible or are we just delaying the inevitable? We paid for a new roof once already and would prefer not to do a new one after only a couple years.
During the various leaks we did determine that the walls have a poly vapour barrier behind them, so right now we think the moisture is coming out through the ceiling only.
Thanks
You are correct that open cell foam does not act as a vapour barrier so you would need to add one. I think vapour barrier paint or vapour barrier retarder would be a smart next move. we used it on our Edelweiss demonstration home and are very happy with it.
Here is our article explaining how vapour barrier paint works for a better understanding, but suffice to say it isn't a bogus product, it actually does work. Older homes with several layers of oil paint have no poly vapour barriers either and the paint does the job. I think that's the right next step for you, and if you do it please report back and let us know how it goes next winter.