Attached garage vapour barrier

Cam Craig · 11-07-13, 12:36 PM

I live in Northern Ontario along Lake Superior (Heat in fall/winter but never air conditioning). I am looking to insulate and vapour barrier my attached garage. I will keep the heat low in the finished garage turning it up when I go out to work in this workshop garage. I will vapour barrier and insulate as well. I plan to use batt insulation to insulate the 3 exterior walls with vapour barrier on the warm side. I will vapour barrier the ceiling with R-40 blown-in insulation above.
My question is about finishing the common wall between the home and garage. The wall currently has vapour barrier on the warm home side with batt insulation in the 5 1/2" wall cavity. When finishing the garage should I leave the vapour barrier off the common wall on the garage side? My understanding is that I should never vapour barrier both sides of the wall. Seeing that the garage will always be an equal or lower temperature than the house it makes sense to me that I should leave the vapour barrier off the garage side of the common wall. I plan to drywall, tape and paint the garage side of the common wall but wondered if a tyvek type material should be appliet first? I want to make sure I do it right! Thanks.

stevehull · 11-07-13, 01:01 PM

VERY interesting question. Had to chuckle when you described that you heat in fall and winter. My thought would be 11 months a year!

You got the right idea when you spoke of putting a permeable barrier on the common wall (between house and garage). In your geographical area (low dew points almost all year), the vapor barrier in the other garage walls should be on the "warm" side. In your case, this would be on the inside or closest to the occupied space.

Be assured that there are high levels of moisture outgassing from the house (even with a vapor barrier correctly installed). Trapping any of this in the wall between house and garage will cause problems. Because the garage is mostly unheated, this moisture (if trapped) will freeze in the winter and will contribute to mold issues.

Not a large investment to purchase just a few sq yards (meters) of house wrap for the common wall . . . .

Steve

Cam Craig · 11-07-13, 09:56 PM

Thanks for your thoughts Steve

11-07-13, 12:36 PM	#1
Cam Craig Lurking Renovator Join Date: Nov 2013 Location: Marathon, Ontario Posts: 2 Thanks: 1 Thanked 0 Times in 0 Posts	Attached garage vapour barrier I live in Northern Ontario along Lake Superior (Heat in fall/winter but never air conditioning). I am looking to insulate and vapour barrier my attached garage. I will keep the heat low in the finished garage turning it up when I go out to work in this workshop garage. I will vapour barrier and insulate as well. I plan to use batt insulation to insulate the 3 exterior walls with vapour barrier on the warm side. I will vapour barrier the ceiling with R-40 blown-in insulation above. My question is about finishing the common wall between the home and garage. The wall currently has vapour barrier on the warm home side with batt insulation in the 5 1/2" wall cavity. When finishing the garage should I leave the vapour barrier off the common wall on the garage side? My understanding is that I should never vapour barrier both sides of the wall. Seeing that the garage will always be an equal or lower temperature than the house it makes sense to me that I should leave the vapour barrier off the garage side of the common wall. I plan to drywall, tape and paint the garage side of the common wall but wondered if a tyvek type material should be appliet first? I want to make sure I do it right! Thanks.

11-07-13, 01:01 PM	#2
stevehull Steve Hull Join Date: Dec 2012 Location: hilly, tree covered Arcadia, OK USA Posts: 826 Thanks: 241 Thanked 165 Times in 123 Posts	VERY interesting question. Had to chuckle when you described that you heat in fall and winter. My thought would be 11 months a year! You got the right idea when you spoke of putting a permeable barrier on the common wall (between house and garage). In your geographical area (low dew points almost all year), the vapor barrier in the other garage walls should be on the "warm" side. In your case, this would be on the inside or closest to the occupied space. Be assured that there are high levels of moisture outgassing from the house (even with a vapor barrier correctly installed). Trapping any of this in the wall between house and garage will cause problems. Because the garage is mostly unheated, this moisture (if trapped) will freeze in the winter and will contribute to mold issues. Not a large investment to purchase just a few sq yards (meters) of house wrap for the common wall . . . . Steve __________________ consulting on geothermal heating/cooling & rational energy use since 1990 Last edited by stevehull; 11-07-13 at 04:51 PM..

11-07-13, 09:56 PM	#3
Cam Craig Lurking Renovator Join Date: Nov 2013 Location: Marathon, Ontario Posts: 2 Thanks: 1 Thanked 0 Times in 0 Posts	Thanks for your thoughts Steve