Basement insulation - tar paper stays or goes?

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Posted by: from Toronto
2/22/2016 at 10:40:42 AM

I recently pulled off old wood paneling in my basement, and would like to insulate it using rigid foam (silverboard or durofoam). Behind the panelling, there is tar paper, and 1x2" studs approximately every 1.5 feet. I see the tar paper as extra protection/moisture barrier, and am inclined to install the rigid foam over top. I have gotten such a range of advice on this...

Option 1) keep tar and studs, fasten rigid board on top leaving a 1-inch air gap between the wall and foam - and build a frame in front of foam for drywall.

Option 2) remove tar paper and all studs, adhere foam directly to cement wall and build out from there.

Option 3) remove studs, adhere foam to tar paper directly.

Option 4) cut foam to fit between existing studs and use tuck tape and expandable foam to fill in spots.

Does anyone have experience with this type of situation? The home is 65 years old. Spray foam is not an option for us.

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Date/Time2/22/2016 at 12:04:47 PM

Hi There!

All depends on your building code calls for R24 for Basement, meaning you would have to use 2"x 6"

and rigid foam 2" and 2"together to achieve that. As for tar paper that can stay. You don't need air buffer it is not a attic space that you want to convert to living space and you are smart not to use spray foam, until they convince as otherwise.

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Date/Time2/22/2016 at 1:04:27 PM

I prefer option 1. You have to make sure there is no moisture coming behind the tar paper. I am from BC and I am not familiar with local building codes. Air space for ventilation is always a good thing.

I don't know if option 3 will work, adhering anything to asphalt is a challenge.



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Date/Time2/22/2016 at 3:32:46 PM

Hi David,

I have plenty of experience in the GTA regarding codes etc. If it were my home, as I suggest to all of my clients. Remove everything. Then inspect the foundation for any existing leaks. If found excavate out side in the spring and deal with that. Now I always use the R-10 ridged foam board glued to the foundation. Then Tuck tape all the seams. You now have a decent vapour barrier as well. Then you can frame with 2x4 studs. with pressure treated base plates over the roll out foam. Then Ramset them in place. You can now use roxul or any other brand you like to insulate in the stud wall, after you have run all of your electrical and plumbing. Cover all water lines and electrical runs with steel cap plates. Then install your drywall. Remember to install the drywall on your ceiling first.

Hope this helps.

James Fram

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David in Toronto
Date/Time2/22/2016 at 5:50:56 PM

What type of R-10 Rigid Foam Board do you recommend? Can I use something like Durofoam Plus, or Silverboard?

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Scott in Brampton
Date/Time2/24/2016 at 9:04:06 PM

Remove everything start new use can foam spray any tie downs spaces between sill plate any plumbing duct or venting leading to the exterior ( forget about the diver bird or ridged foam not enough r vale / Tyvek or typar walls rolls come in 3ft / 9 ft / 10 ft attach to sill plate use hammer stapler frame walls 1in off from exterior walls then insulate with R22 Roxul / you can double it up in joist pockets r44 apply caulking top plate bottom plate corners all double studs ( crucial step ) apply super six poly be sure to make poly tight / tape all seams with Tuck Tape ( red ) you can even tape every stud sealing staple holes / Drywall screws are self sealing so the don't affect vapour barrier ( not if you miss stud though )


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