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Rim joist insulation with rigid foam and Roxul

Posted: Thu Oct 26, 2017 7:41 am
by Navin
Inspired by Shannon's youtube videos on rim joist insulation I started the project in my unfinished basement but had some confusion. I have the following question:
I decided to go with rigid foam and Roxul (rock wool as fire barrier). I am putting rigid foam( 2 inch, R10) first with spray foam at the edges to seal it and then put roxul rock wool as fire barrier. Now the rock wool is facing an un-finished basement. Will rock wool be affected by moisture in winter or summer? If so what to do about it? We are located in NY state north of New York City.

Re: Rim joist insulation with rigid foam and Roxul

Posted: Thu Oct 26, 2017 5:05 pm
by Shannon
No, Roxul is very good at dealing with humidity, it does not want to be wet like most insulations though. Even though your basement may not be finished it should be dry enough to leave the Roxul exposed to the interior.

Re: Rim joist insulation with rigid foam and Roxul

Posted: Fri Oct 27, 2017 7:28 am
by Navin
Thanks Shannon so I will leave it exposed to interior. Thanks for all the wonderful DIY videos.

Re: Rim joist insulation with rigid foam and Roxul

Posted: Fri Oct 27, 2017 9:20 am
by Shannon
you are welcome

Re: Rim joist insulation with rigid foam and Roxul

Posted: Sat Nov 04, 2017 10:02 pm
by red03golf
Here's some extra information in case someone finds it useful:
https://insofast.com/explore/sealing-an ... im-joists/

Re: Rim joist insulation with rigid foam and Roxul

Posted: Wed Apr 18, 2018 7:37 pm
by Uncle Buck
Hi all

Does anyone know if this rigid foam / Roxul method is acceptable by code in Ontario?

I just spent 2 hours fighting with fibreglass, accoutic sealant and vapour barrier around engineered floor joists. It didn't go well....

Re: Rim joist insulation with rigid foam and Roxul

Posted: Wed Apr 18, 2018 10:40 pm
by Shannon
Many areas/cities slightly modify their requirements so the best thing to do is check with your local building authority ,as they will ultimately have final approval over the work.
We would be interested in what they tell you as well if you want to post back after.

Re: Rim joist insulation with rigid foam and Roxul

Posted: Thu Apr 19, 2018 6:31 am
by Uncle Buck
Will do

My read of the Ontario code suggests it might not fly. Looks like it always wants vapour barrier over the batt insulation. Perhaps it's more for protection and would not need to be sealed if there is sealed rigid foam behind it.

9.25.2.3

(7) Except as permitted in Sentence (8), insulation and vapour barrier shall be protected from mechanical damage by a covering such as gypsum board, plywood, particleboard, OSB, waferboard or hardboard.

(8) In unfinished basements, the protection required in Sentence (7) need not be provided for mineral fibre insulation, provided it is covered with polyethylene vapour barrier of at least 0.15 mm in thickness.

Re: Rim joist insulation with rigid foam and Roxul

Posted: Thu Apr 19, 2018 7:09 am
by Shannon
The 2" sealed rigid foam should change the requirements. It is generally considered a air/vapour barrier in most places once it is sealed with canned foam. You should check with the dept. in person to be sure.

Re: Rim joist insulation with rigid foam and Roxul

Posted: Fri Apr 20, 2018 9:05 pm
by tpirovol
Interested as well in the same boat in the GTA. Also the 2" foam do you prefer the Dow Blue or Pink Corning? In the end I am going to do the same thing 2" foam sealed with expanding foam then Roxul.

Thanks T

Re: Rim joist insulation with rigid foam and Roxul

Posted: Fri Apr 20, 2018 9:08 pm
by tpirovol
Uncle Buck wrote:
Wed Apr 18, 2018 7:37 pm
Hi all

Does anyone know if this rigid foam / Roxul method is acceptable by code in Ontario?

I just spent 2 hours fighting with fibreglass, accoutic sealant and vapour barrier around engineered floor joists. It didn't go well....
I did the same thing and just couldn't get it right. 3 years after I did it I went downstairs and noticed water running down the vapor barrier. The Roxul had stuck to the wood in the Rim joist and caused mold in a few. Took it all out, cleaned the mold and had it open ever since. Now that I am finishing the basement want to insulate properly. Keep in mind that year it was very very cold like -25+ so it was an unusual year.

Thanks T

Re: Rim joist insulation with rigid foam and Roxul

Posted: Sun Apr 22, 2018 8:20 am
by Shannon
tpirovol wrote:
Fri Apr 20, 2018 9:05 pm
Interested as well in the same boat in the GTA. Also the 2" foam do you prefer the Dow Blue or Pink Corning? In the end I am going to do the same thing 2" foam sealed with expanding foam then Roxul.

Thanks T
I don't think there is any difference between the two other then the name on the exterior and the color.

Re: Rim joist insulation with rigid foam and Roxul

Posted: Sun Apr 22, 2018 8:21 am
by Shannon
tpirovol wrote:
Fri Apr 20, 2018 9:08 pm
Uncle Buck wrote:
Wed Apr 18, 2018 7:37 pm
Hi all

Does anyone know if this rigid foam / Roxul method is acceptable by code in Ontario?

I just spent 2 hours fighting with fibreglass, accoutic sealant and vapour barrier around engineered floor joists. It didn't go well....
I did the same thing and just couldn't get it right. 3 years after I did it I went downstairs and noticed water running down the vapor barrier. The Roxul had stuck to the wood in the Rim joist and caused mold in a few. Took it all out, cleaned the mold and had it open ever since. Now that I am finishing the basement want to insulate properly. Keep in mind that year it was very very cold like -25+ so it was an unusual year.

Thanks T
The rigid foam must be sealed and I really would not add poly vapour barrier if you are using 2" rigid.If the local code insists then I would use 1" rigid foam instead of 2"

Re: Rim joist insulation with rigid foam and Roxul

Posted: Mon Jan 21, 2019 5:02 pm
by compaholic
My wife and I just recently bought a cape home built in 1957. After moving in we noticed how incredibly drafty the home is and inspired by Shannon's Youtube video I added the rimjoist project to my to do list. I have started with caulking the rim joists/sill plate and using great stuff for the larger holes such as pipes, conduit's, & wiring coming in from the sides. I plan on doing the rigid foam at a later time but I don't remember what the recommendation is for the sides of the home where the joists run parallel to the foundation. This is a tight and awkward area where I can't even get the caulk gun or bottle of great stuff to fit in there. What is your recommendation for the joists that run parallel to the foundation?
I've read that this area does not have as much leakage as the rim joists. Could I just stuff rock wool in there? Thanks.

Re: Rim joist insulation with rigid foam and Roxul

Posted: Mon Jan 21, 2019 6:22 pm
by Shannon
These ends are more difficult to deal with like you said and when you have limited access about all you can do is install Roxul and vapour barrier .

Re: Rim joist insulation with rigid foam and Roxul

Posted: Fri Feb 01, 2019 9:46 am
by hcpatel78
compaholic wrote:
Mon Jan 21, 2019 5:02 pm
My wife and I just recently bought a cape home built in 1957. After moving in we noticed how incredibly drafty the home is and inspired by Shannon's Youtube video I added the rimjoist project to my to do list. I have started with caulking the rim joists/sill plate and using great stuff for the larger holes such as pipes, conduit's, & wiring coming in from the sides. I plan on doing the rigid foam at a later time but I don't remember what the recommendation is for the sides of the home where the joists run parallel to the foundation. This is a tight and awkward area where I can't even get the caulk gun or bottle of great stuff to fit in there. What is your recommendation for the joists that run parallel to the foundation?
I've read that this area does not have as much leakage as the rim joists. Could I just stuff rock wool in there? Thanks.
Yes. It is a pain job. Took me the whole week to finish 70 joist cavity. Then after I found this video. It did not came at the right time for me, but I thought you will get benefited.
https://www.youtube.com/watch?v=8DetrFoTji8

Re: Rim joist insulation with rigid foam and Roxul

Posted: Fri Feb 01, 2019 4:53 pm
by Shannon
Yes that works if you can see in the area you are working. If you cant see what you are doing then I think you are wasting your money on the foam.