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Old 10-06-2008, 09:40 AM   #1
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Inulation & R value


I am sealing the basement header area as part of an energy efficient rebate. The requirement is to be at least R-20. I have a commercial roll of R-17, but I'm guessing from what I've read so far that doubling it up doesn't increase the R value?

If anyone has any info one way or the other, please post.

tyvm
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Old 10-06-2008, 10:02 AM   #2
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Inulation & R value


R-Value usually does improve as you get thicker insulation. Fiberglass 3.5" is about r-13/15 where 9.5" is r-30 or more.

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Old 10-06-2008, 01:47 PM   #3
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R-Value usually does improve as you get thicker insulation. Fiberglass 3.5" is about r-13/15 where 9.5" is r-30 or more.
This makes sense, but does that also mean that using two layers of R17 will make for (inspection wise) an R value of more than 20?
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Old 10-06-2008, 05:34 PM   #4
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This makes sense, but does that also mean that using two layers of R17 will make for (inspection wise) an R value of more than 20?

Don't know why it wouldn't, except you might need to establish that its more than one layer and educate the inspector to that end.

FYI; the R-standard was pretty much written to the benefit of the fiberglass batt industry. R-value decreases markedly with moisture content among other factors. So if you really want to insulate (and not just score a rebate) take steps to exclude moisture and maintain loft. R-value is just a number and in real world applications rigid insulation of a lower R-value will greatly outperform f/g batting.
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Old 10-06-2008, 07:11 PM   #5
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Inulation & R value


Awesome. Thank you both for your help. I will go ahead and double up the R-17 and do my best to make sure it's sealed to keep the moisture out. Rigid foam would be cool, but I think since I've already got the giant roll of R-17 I'll use it up for this job. Hopefully the inspector will be happy with it, but like you said having it done well will be worth more than the rebate in the long run either way.

Thanks again,
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Old 10-06-2008, 07:45 PM   #6
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Inulation & R value


how THE #'S WORK

R= (T/K) +R ( EVEN THE KRAFT PAPER HAS SOME R VALUE)

T is thickness

K is thermal conductivity... this is a (factor ...a number) at a given mean temperature and relative humidity. typically ( a bell curve ) Many K factors and thus R values are computed at 75 degrees F at 65% RH.

Yes R17 + R17 + R17 = 3 X R17

PS IF THE INSULATION: is faced and you want to double it....slash the facing or remove it on the second layer so you are not trapping humidity and raising the K value higher.

Last edited by Big Bob; 10-06-2008 at 08:03 PM.
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Old 10-06-2008, 08:43 PM   #7
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Inulation & R value


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Originally Posted by dano_o View Post
I am sealing the basement header area as part of an energy efficient rebate. The requirement is to be at least R-20. I have a commercial roll of R-17, but I'm guessing from what I've read so far that doubling it up doesn't increase the R value?

If anyone has any info one way or the other, please post.

tyvm
Dano
Would you mind informing us of this energy efficient rebate?? Is this specific to where you live? Your avatar doesn't indicate your location.

Are you speaking of the rim joists when you say basement header? Just finishing up my rim joist project myself. Thanks.
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Old 10-06-2008, 09:07 PM   #8
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Would you mind informing us of this energy efficient rebate?? Is this specific to where you live? Your avatar doesn't indicate your location.

Are you speaking of the rim joists when you say basement header? Just finishing up my rim joist project myself. Thanks.

This is for Canada. Currently the rebate is set out as follows (pdf link)
http://oee.nrcan.gc.ca/publications/...lify-grant.pdf

Yep, it's the basement header that I'm filling up that they were specifying R20+.

Nice Big Bob, that's great to hear. I'm not sure if the commercial roll I have is faced or not, but if it is I'll cut away one side of each layer to make sure I'm not trapping any moisture. Thank you!

Dano
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Old 10-06-2008, 10:20 PM   #9
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Inulation & R value


dano -

Just hope the inspector is dumb enough to fall for the doubling snow-job up while compressing the fiberglass.

From the real world - about 1/2 to 1% moisture can cut the insulation value of fiberglass in half. It has little effect on extruded foam.

Personally, I would cut 1" or 2" foam close to fitting, foam the cracks to cut off the infiltration and then jam in the foam using the adhesive properties to hold it in place. Then use 1 layer of your R17 fiberglass to fill the remaining space - getting about an R-value (R22 to R27).

Last edited by concretemasonry; 10-08-2008 at 07:38 PM.
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Old 10-08-2008, 05:50 PM   #10
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Here in my neck of the woods everyone pays to have the rims shot with foam. "only the best will do"
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Old 10-09-2008, 10:37 AM   #11
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Personally, I would cut 1" or 2" foam close to fitting, foam the cracks to cut off the infiltration and then jam in the foam using the adhesive properties to hold it in place. Then use 1 layer of your R17 fiberglass to fill the remaining space - getting about an R-value (R22 to R27).
I did similarly to this but first caulked the inside of the rim joists, recut existing fiberglass batts to proper size, then inserted 2" foam and then sealed the edges again with caulk or foam.

This solves my sealing and insulating of the rim joist. At the present, this may be against code? Something I wasn't aware of until I was nearly 90% finished. I wanted a more finished look. I also believed that it would be better sealed if placement was in this order and better r-value. Not everything you find on the internet is the correct way.

Eventually I'll get around to sheetrocking over the top when the basement is finished. Which I believe will then make it code compliant for fireproof reasons. Though not planned anytime soon however.
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Old 10-09-2008, 02:10 PM   #12
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My method was meant to make the sealing/caulking/foaming of the rim joist a single step by putting in the foam first for complete elimination of infiltration. This results in having fiberglass over the foam. Granted, fiberglass is not a barrier to flames or fire, but it is better than nothing until it gets covered up.
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Old 10-09-2008, 02:27 PM   #13
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are you guys talking about spray foam or sheet foam?

edit-
ive been hearing more and more that its worth it to pay a pro to do the insulation right rather than DIY.

Thoughts?
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Old 10-09-2008, 06:20 PM   #14
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Originally Posted by troyce1 View Post
are you guys talking about spray foam or sheet foam?

edit-
ive been hearing more and more that its worth it to pay a pro to do the insulation right rather than DIY.

Thoughts?
We were talking about foamboard (2" in my case) and then sealing the edges with caulk or foam (Great Stuff or similar).

I'm very confident that I have improved my situation immensely! They previously were not sealed and had only FB batts. Not to mention that my DIY work saved me hundreds of dollars! That's even if I wanted to do the spray foam myself.

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My method was meant to make the sealing/caulking/foaming of the rim joist a single step by putting in the foam first for complete elimination of infiltration.
Good point.

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