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awhitehouse 08-22-2009 05:30 PM

Vapor Barrier Question

I am insulating an outbuilding I have. I know that traditionally the vapor barrier goes on the "warm in the winter" side and that is how I am handling all the exterior walls.

However, I have 2 twists on this I need help with:

1. The outbuilding will be divided into 2 halves on the main level and separated by a wall. One side will be a garage and the other a workshop. Both will be heated, but to different temperatures. The garage will be kept at just above freezing (35-40 F or 2-4 C) while the shop will generally be kept around 55 F/12 C when I am not using it and around 65-70 F/18-21F when I am in there or need the extra heat. So which side does the vapor barrier go on?

2. There is also a loft that I want to turn into a "guest house". It is above both the garage and the shop. Most of the time it will be keep it just above freezing so the pipes don't freeze, however when someone is staying there it will be whatever temperature is comfortable for them. Which side does the vapor barrier go on in this case?

These ones have me puzzled. Any help would be great.


slownsteady 08-22-2009 07:12 PM

Hi Alan,

I can certainly respect your privacy concerns, but it might be helpful to know what part of the world you live in, especially for a heating / insulation question.

But that being said, you probably don't need a vapor barrier between the two halves, since it is technically an interior wall, even if it is block or concrete. There are many folks on here who can argue against a vapor barrier at all. But I'll leave that to them.

awhitehouse 08-23-2009 08:43 AM

I am in the southern Ontario area. Warm humid summers (except this summer which has been crap) and cold, snowy winters.

GBR 08-23-2009 05:01 PM

I'd definitely put it on the garage sides to keep the water from the cars going to the warmer spaces. Even using a v.b. paint to keep the water out of the walls in the first place. All that water, snow on a vehicle wants to go somewhere as moisture, especially if the garage is heated. Be safe, G

slownsteady 08-27-2009 11:32 AM

Good point, GBR. I hadn't even thought about from that point of view.

awhitehouse 08-28-2009 05:40 PM

Thanks for the information. It helps.

I actually did call the building department here. The person (who sounded like they were 16) on the other end basically said "good question" and then after a lot of "hmmms" and "ummmms" gave me the answer about going with vapor barrier in the shop side of the wall and on the top of the insulation for the loft.

But the answer didn't give me a lot of confidence in what to do. So I have posted her and a couple other boards. Unfortunately I have gotten answers saying both shop side and garage side and both are convincing arguements (garage side says melting snow and ice and rain water is more moist than the shop so put vapor barrier on that side).

I am leaning towards just using rigid foam insulation between the shop and the garage. Then the issue of the vapor barrier goes away. It is a small enough wall that the extra costs won't break me. However, for insulating the loft, I am still at a loss of what to do.

inspectorD 08-29-2009 08:52 AM

Since I am not there and cannot possibly see the condition of the shop. This means I can't really give you an opinion. There are many variables to deal with noone has brought up. The condition of the roof? does it leak? How is the ventilation? How big and drafty are the garage doors, how often do you go in and out?, Is there a vapor barrier under the slab of the concrete? What is the orientation of the building to solar gain...if any? These are just a start.

Do yourself a favor and get it right, hire a professional for a couple hundred dollars and have someone actually look at your project,it will be $ well spent to ward off potential issues down the road. And what to look for if you start to have problems.
Try for a start, they will look at your issue and give professional advice...on scene.:)
Good luck, we all want a warm shop.;)

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