SW Ontario | Deepfreeze - 11/24/2022 17:17
The OP’s question was about adding house wrap. If you have a vapor barrier behind drywall and put house wrap on the sheathing, your wall will rot because as you stated the wall has to dry to the outside. The reason for this problem is that 99.99% of the installed vapor barriers are ineffective at preventing 100% moisture migration due to how we install the barrier with staples and do not seal over the staples, then we cut holes for switches and outlets in the barrier and cannot seal the vapor barrier to the outlet nor seal the holes in the back of the electrical box where the cables enter it and lastly, even if everything else on the installation was perfect we put dozens of drywall screws through the vapor barrier.
I'm sorry but there is a lot of incorrect information here. House wrap will not cause the house to rot because house wrap is vapour permeable. Even with the house perfectly sealed with house wrap it will still allow passage of vapour so that the wall can dry. As for holes in the vapour barrier, they generally seal around the fasteners when you install them. If you remove the fasteners then yes you will have a hole in the barrier. Modern construction also uses sealed electrical boxes to avoid what you stated. You can also do this by taping your boxes before installation and using a bit of spray foam where the cables enter the box. As for drywall screws, refer to my previous point. The vapour barrier will form a pretty good seal against the fastener.
Deepfreeze - 11/24/2022 17:17
This is why closed cell spray foam is so effective if installed correctly. The 100 penetrations on every 10’ of wall to install drywall are effectively within the conditioned space of the home. Moisture does not have the opportunity to reach a cold surface and condense. Within a spray foamed wall though, very hard types of lumber like old growth Douglas fir and southern yellow are a little like having steel studs and they will be a cooler surface within the enclosed stud cavity but generally not cold enough to condense moisture.
Spray foam is only effective in a house that doesn't move. Otherwise the movement of the house will cause cracks in the spray foam, which will seriously degrade its insulation and vapour barrier properties. Also, your statement about studs not gernerally being cold enough to cause condensation is highly location specific. I can tell you that it is not true where I live. |
House Wrap-How Much Does it Help?
