1 1/2 Storey House - Insulate Attic Crawlspace


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Old 06-04-14, 07:55 AM
C
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Question 1 1/2 Storey House - Insulate Attic Crawlspace

Hi all. I have a 1940's 1 1/2 storey house, and the attic crawlspace does not have insulation on the interior knee wall or above the ceiling. It does have some blown in stuff between the floor joists.

I would like to insulate the knee wall and slide some rigid foam insulation above the ceiling (as far as I can get it to go). I was thinking of using bat insulation on the knee wall (to save $). The knee wall is finished with lath and plaster on the interior side. I am in Canada and will definitely have some very cold winters and hot summers.

What I am wondering is how/if I should apply a vapor barrier to the attic-side of the knee wall? Also, any other tips or suggestions for this project?

Thank in advance!
 
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Old 06-04-14, 10:52 AM
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The drawing at the bottom of the link below should help. Maintaining a ventilation path is important along with air sealing as many leaks as possible.

Now is not the time to be installing the cheapest insulation, your time and effort are worth more and the purpose of this is to improve comfort and reduce energy costs. Consider Roxul for a batt solution, but get a quote from a company that can install a fabric across the back side and blow in insulation. The fabric will be vapor permeable and not a vapor barrier. And they have very skinny workers who can get all the way into that space to do it all right. And, often not a lot more expensive than DIY, certainly easier.

The vapor barrier, if you install one would go to the warm side of the insulation, not the attic side. Most paints will provide an adequate solution. Air leakage is the larger problem.

http://web.ornl.gov/sci/roofs+walls/...c%20floors.pdf

Bud
 
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Old 06-04-14, 12:43 PM
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Thanks Bud. I will definitely try get the best R-value for my money, but would really prefer to do this myself. I can rent an insulation blower from home depot if that is the option that provides the best R-value for my money.

So the paint on the interior side of the knee wall is probably an adequate vapour barrier eh? But I should still put a layer of poly onto the attic-side of the knee wall to cover up air leaks. I would have to wrap/bend the poly around each stud and press it against the backside of the lath and plaster, thus allowing the batt insulation to fit between the studs. Then I will probably have to nail some wood strapping (or use the felt matting you mentioned) to hold the batts in place.

Does that sound correct? Thanks again for your help!
 
 

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