Rim Joist Insulation With Different Method Using Rigid Board

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Manyakus
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Rim Joist Insulation With Different Method Using Rigid Board

Post by Manyakus » Mon Jan 28, 2019 8:00 am

Hello,

What is the reccomended method between Option "A" or Option "B" when using 2 in XPS (pink board).
Can the uncovered section of the sill plate be uncovered as shown in Option "A"?
Or I need to cover the sill plate as shown in Option "B"?
Is Option "C" the best method if I want to achieve R20 value assuming its R5 for every 1 in ?

Thanks!
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Shannon
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Re: Rim Joist Insulation With Different Method Using Rigid Board

Post by Shannon » Mon Jan 28, 2019 4:41 pm

Option C is your best option ,but remember all rigid foam must be covered and protected from fire with a separation from the living space. So if you have a fire rated ceiling system like drywall then you are good if not that foam must be covered with something like Roxul insulation. Same goes for the wall, so if you have to frame the wall and cover with drywall to protect from fire then I would omit one layer of 2" rigid from the wall to save costs and then insulate the wall cavity. In some areas the 2" rigid foam may be able to replace an air/vapour barrier so check that with your local permit office.
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Manyakus
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Re: Rim Joist Insulation With Different Method Using Rigid Board

Post by Manyakus » Tue Jan 29, 2019 7:13 am

Yes I will cover with Drywall for the wall and ceiling, so they will be covered.
So for the wall its gonna be one layer of 2in foam + roxul bat between the studs + NO VAPOR BARRIOR + drywall. (I dont need vapor barriour since my foam is 2 in right?)
As for the rim joist, you suggest Option C, which I will do.
However I have a small section of my basement where my rim joist are problematic (had trouble mold in the past), so can I overkill a small section of my problematic rim joist (maybe 8 feet) like in Option D? Is there a such thing as bad overkill insulation?
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Shannon
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Re: Rim Joist Insulation With Different Method Using Rigid Board

Post by Shannon » Tue Jan 29, 2019 8:35 am

I see no problem with the multiple layers. As for the no vapour barrier ,like I mentioned earlier some areas will not allow 2" rigid to be the vapour barrier so you should check with your local building code office.
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Manyakus
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Re: Rim Joist Insulation With Different Method Using Rigid Board

Post by Manyakus » Tue Jan 29, 2019 8:53 am

I live in Montreal and the Quebec code is the Canadian National Code with some minor amendment and written in French. To get this copy its 350$ and same thing for Canadian National Code which is aroun 400$. We do not need to get permit in QC to do these kind of reno and there is no inspector/inspection that is done when a reno is finished unless it is for plumbing/structural then you need a permit but still no inspestor will come to see your work.
So I am kind in a loose area where I want to know what is the code but I need to pay 350$ to know this information which is unacceptable in my opinion.
Anyone has the Canadian National code? The only thing I can find online is the 1995 version which is too old.

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Shannon
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Re: Rim Joist Insulation With Different Method Using Rigid Board

Post by Shannon » Tue Jan 29, 2019 10:01 am

The national code book does not cover this specifically and that is why different locations put their own interpretation on what the code book says about what would be appropriate or not.
IMO If I was using well sealed XPS 2" rigid foam in my wall assembly I would not add another interior air/vapor barrier.

Here is a little reading for you.https://www.ecohome.net/guides/2254/pol ... to-use-it/
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hcpatel78
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Re: Rim Joist Insulation With Different Method Using Rigid Board

Post by hcpatel78 » Fri Feb 01, 2019 9:39 am

I recently did finish basement In Northern NJ -USA. I have used 2" rigid foam in rim joist. It's hard to cover with drywall as per code so, I went with ROXUL R15 batts stacking behind the rigid form in the cavity until it sits flush to the inside basement wall. I ended up using 5 more bundles of Roxul for 1000 Sq. Ft basement rim joist. Every cavity took 3 pieces of 9"x14.5" piece of ROXUL. The township inspector validated the roxul as a fire barrier instead of drywall. Please see attached pictures.
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Shannon
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Re: Rim Joist Insulation With Different Method Using Rigid Board

Post by Shannon » Fri Feb 01, 2019 4:50 pm

Yes Roxul is for sure a fire retardant product.
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Manyakus
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Re: Rim Joist Insulation With Different Method Using Rigid Board

Post by Manyakus » Mon Feb 04, 2019 1:13 pm

Nice Job!
That's what I am planning to do!

I've heard that the duct work that are in touch with the roxul at the rim joist must be super well sealed in order not to suck and blow roxul fibre in the duck work of the house.

Is that true?
Considering that the MSDS of Roxul state that any repeated exposure of their product can cause cancer in animals?

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Shannon
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Re: Rim Joist Insulation With Different Method Using Rigid Board

Post by Shannon » Mon Feb 04, 2019 6:45 pm

I think that would be a very minor issue. They really should not be sucking at hot air lines there is only pressure there. You can tape the boot to pipe joint though if you like.
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lariviere
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Re: Rim Joist Insulation With Different Method Using Rigid Board

Post by lariviere » Tue Feb 12, 2019 6:36 am

Thanks again Shannon

One last question about the foam. Does it need to lay perfectly flat against the concrete? There are of small ridges and bumps from the forms, it will be impossible to have the foam board be tight to the wall.

And just a FYI for readers if you live near the US border you get Owens 2” Foamular board for $24 / sheet in bulk pricing.

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Shannon
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Re: Rim Joist Insulation With Different Method Using Rigid Board

Post by Shannon » Tue Feb 12, 2019 8:20 am

those small bumps are fine.
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