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Sergeant Rock
Member
# Posted: 7 Nov 2019 21:36
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Hi all, I am new to the forum. I hope someone can answer my question. I have an insulated, 12' x 14' outbuilding complete with vapor barrier. I use it for a small shop area and never heat it. Recently i added an addition utilizing one side of my out building. I am going to use this addition for a warm up shack heated with a wood burning stove. My question is, what do I do with the interior wall of my warm up shack that is the exterior wall of my out building? So far the wall has been strapped. Should I just sheet it or should i insulate and vapor barrier it before I sheet it.? I know the vapor barrier should be on the warm side but in this case I am stumped as there is already vapor barrier on the existing wall.

Brettny
Member
# Posted: 8 Nov 2019 07:19
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The wall in question is alreaty insulated? Leave it as is. I sulate the other 3 walls of the wood stove room. If you put a box fan in a doorway between both of those rooms you could heat it with one heat source.

Blow cold air towards the stove.

Sergeant Rock
Member
# Posted: 8 Nov 2019 10:52
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Thanks for your reply however there is no doorway in the wall. There is a separate entrance to the out building.

razmichael
Member
# Posted: 9 Nov 2019 08:40
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The potential issue (and I'm no expert) is the vapor barrier on the shared wall. Generally inside air in winter has way more moisture in it because it both can hold more moisture and the general humidity from living. This is why the VB is on the warm side - so moist, warm air does not condense into the insulation as it cools down going through the insulation to the outside wall.

In your case, as the main shed is rarely heated, the VB is not doing much but if the attachment is heated at times, the warm, moist air in that part will go through the adjoining insulation and start to condense within it and against the VB.

I don't know the best solution. I think I would ensure the addition adjoining wall was VB'd or sealed from the old structure. Whether you added more insulation or not would depend on how much you wanted. Spray foam is an alternative but costly and not likely applicable for that small a structure (although you did not mention the size). Basically, although you are using a shared wall, you might want to treat both as separate buildings (maybe without added insulation on the one wall depending on the current amount).

There are often numerous discussions on the use of VBs in general. It is hard to put them in without some leaking. In places like I'm at, where the temperature swings from -40C in winter to +40C in summer at times, you can see that summertime, with hot humid outside air and the air conditioning on high, the VB is actually causing just what you want to avoid. For this and many more reasons, properly selected and installed spray foam is becoming so popular (especially as the cost slowly decreases).

Sergeant Rock
Member
# Posted: 9 Nov 2019 13:45
Reply 


Thanks for the reply. I was leaning toward just vapor barrier on the shared wall. At least that would limit the amount of condensation from the warm up room. However I do realize that will be creating a trap for moisture. As we will not be living in the new warm up room conditions of humidity would only occur during use. Ideally I should remove the existing vapor barrier from the shared wall but that would entail removal of interior sheeting and that is not an option.
You mentioned -40C to + 40C. You must live in the same area as I do. lol

razmichael
Member
# Posted: 9 Nov 2019 16:14
Reply 


Same country! Ontario w cabin in Quebec.

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