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Old 11-22-2009, 07:47 PM   #1
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insulating my out building


i have recently bought this house and in the back yard theres a 16'x24' building and have started to finish it. the walls were insulated by the previouse owner and then they covered it with osb but no vapour barrier over the insulation so i have pulled all of the walls to add the vapour barrier and replace with drywall. behind the insulation they had stapled tar paper on the interior side of the exterier sheathing between all the studs, my question is can i leave it there or would it be highly recomended that i pull the insulation out, remove the tar paper and put the insulation back in befour adding my poly vapor barrier??

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Old 11-23-2009, 06:55 AM   #2
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insulating my out building


A lot has to do with where you are located...tell us that and we can tell you more.

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Old 11-23-2009, 06:59 AM   #3
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insulating my out building


What is the use for the shed?? Does it really need insulation, will it be heated?? I would remove the tar paper on the inside of the exterior sheathing, then insulate and vapor barrier as per usual.
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Old 11-23-2009, 08:06 PM   #4
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insulating my out building


i live on the along the coast of vancouver island so it can get pretty humid here all year round. it will be heated we are turning it into an inlaw suite, nothing special just a living room and a bedroom in the back.
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Old 11-23-2009, 08:56 PM   #5
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If I read your description correctly, the tar paper is on the exterior side of the insulation?
If so, I see no reason to remove it.
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Old 11-24-2009, 06:46 AM   #6
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OK; I consider you to be ina relatively mild (compared to us) climate zone but nowhere near somewhere like Atlanta or Florida. You get appreciable amounts of rain (unlike Florida) but you have to heat during the winter and cool during the summer (unlike Atlanta)...right?

If so, then you have to have insulation and protect your house from water infiltration, so obvious things like good drainspouts and air barriers are vital; but the control of interior humidity levels is somewhat less important owing to the general higher levels of humidity everywhere, so vapour barriers or retarders seem doubtful. That's probably why you don't have one now on the inside. Keeping the humid air inside only makes your air conditioner work harder...

On the other hand, preventing even more humid outside air from getting in is why you'll have an air barrier (nowadays we speak of Tyvek and plastic wraps like that) but in the olden days, felt paper was the equivalent pretty well everywhere, acting as an air and water penetration barrier placed just behind the outer shell, whether it's brick or siding. Just prevents rain from getting in. So thats OK...

So removing that is a mistake; so is adding a vapour barrier on the inside.

And I'll add again that without knowing where you are located, it is impossible to tell you what methods your climate calls for. There is no one simple answer and once you know the zone the decisions made follow.
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Old 11-24-2009, 08:02 PM   #7
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im about 40 kms away from vancouver, definatley heat in the winter but we wont be cooling in the summer. there is a wrap around the building underneith the siding which i will defenetly be leaving but they also have the paper on the other side of the sheathing inside the building. to my understanding i want the vapour barrier between the drywall and the insulation, anywhere hot meets cold i guess to avoid condensation, correct??
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Old 11-24-2009, 08:11 PM   #8
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Not only to avoid condensation, but to prevent moist air from reaching it's dew point. Moist interior air will travel into the wall and where it reach the dew point it will create condensation. In heating climates this point is toward the exterior of the wall.
I'm not familiar with the Vancouver climate, but I would say your correct in placing an interior poly vapor barrier and I also think you can leave the tar paper in place. It serves no purpose, but I don't think it is doing any harm either.
So there you have it, two conflicting opinions....lol
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Old 11-25-2009, 06:05 AM   #9
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OK, well then more heating than cooling calls for a vapour 'barrier' of some sort, and whether you choose a vapour barrier (such as a low-perm 6 mil poly sheet like we use here, or a vapour retarder (which may be anything from a coat of paint to tar paper) it will prevent moist interior air from condensing with the cold surface on the outside.

Down south, where it's hot and humid, as opposed to just humid, all they need is a vapour retarder - and that can be as I said a coat of paint on the inside, or lined drywall or something that has a medium-perm value, to let some humidity out without overtaxing the cooling system. Where we are, we use the 6mil poly sheet...

Maybe back in the days when the shed was built, thay had a choice of putting paper where they did, so they did that. Fact remains that you'll probably need something to control the air movement (and the Tyvek or paper wrap does that on the outside) and something to prevent the humid air from condensing, now that you are insulating.

If you put a poly sheet directly under the drywall, then put insulation under that, you should have a tight space. It may become warmer than you expect during the warm season, so dehumidifiers and lots of flow-through ventilation may be needed.
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Old 11-25-2009, 08:38 AM   #10
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insulating my out building


Quote:
Originally Posted by ollgoater View Post
i have recently bought this house and in the back yard theres a 16'x24' building and have started to finish it. the walls were insulated by the previouse owner and then they covered it with osb but no vapour barrier over the insulation so i have pulled all of the walls to add the vapour barrier and replace with drywall. behind the insulation they had stapled tar paper on the interior side of the exterier sheathing between all the studs, my question is can i leave it there or would it be highly recomended that i pull the insulation out, remove the tar paper and put the insulation back in befour adding my poly vapor barrier??
Canadian boy here!

The answer seems simple enough.

You need a poly vapor barrier that is certain! But I'm not certain about the tar paper. Your local building codes will determine if it needs to be removed.

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