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Old 02-10-2018, 06:57 AM   #1
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R value


Good Saturday Morning!!

I have a question about R value, our walls in the addition are R21, while walking around in it I noticed the insulators used R11 over doors / windows
I can only guess as to their reasoning and I have a couple ideas, either the cavity wasn't deep enough for R21 or they ran out of it and used whatever else they had.

So... I have in a prior thread asked about insulating small spaces and inquired about the best way, but was given the impression it would make little difference if I tried to increase insulation because we have more window than wall in certain areas.
Now that I see they used a lesser R value above ALL the windows , I will re ask .. is there a way to improve the r value in those locations or is it futile ?
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Old 02-10-2018, 07:21 AM   #2
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Re: R value


Since you started a new thread, I won't go back and try to revisit the older ones. What size stud cavities do you have? 2x4, 2x6, 2x8? R21 is too much for 2x4 and marginal for 2x6, as it will need to be compressed and will lose its insulation qualities when that is done.
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Old 02-10-2018, 07:27 AM   #3
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Re: R value


If you have 2x6 walls but for example 4x10 headers above windows and doors thst is resting on a 2x6 sill... installed on the outer part of the wall, it would leave a 2" deep void that would need to be filled with thin insulation. 2" foam would be better.

I would suggest you remove some insulation or stick a tape measure in there and see what the deal is rather than making us guess.
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Old 02-10-2018, 07:49 AM   #4
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Re: R value


Yes we have 2 x 6 walls, some areas are shallow , under our picture window layout it looks like a header with a additional laminate beam , the wall is cantilevered, this sidetracked my other thread because there is a pic of it , and it is I guess "odd" describes the framing.

so yes foam is what I was thinking, can I use foam & the fiber that's there ?? remove the fiber and add foam then replace fiber ?? will the foam create any moisture issues??
I want to do as much as I can before they sheetrock, but want to be sure not to cause problems.

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Old 02-10-2018, 08:47 AM   #5
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Re: R value


No problem using rigid foam there. It's going to be a little better than fiberglass. Back in the old days, we used to frame headers with a 2x on the outside and a 2x on the inside, and then we would try to fill that gap with fiberglass (we called them "snake coffin headers". Now, we build headers by shifting the 2x material or LVL or whatever to the outside, which allows the insulation to be installed when the rest of the house is insulated. Much better way to go.
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Old 02-10-2018, 08:56 AM   #6
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Re: R value


Been awhile but I just went with 3 of the 2x material with a 1" layer of rigid sandwiched in the middle somewhere. That gave me a nailing surface on both sides and quickly created a great header with descent r-value, about r-10.

Are they actually using high density fiberglass insulation, the r-21 that fits the 2x6 cavities?

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Old 02-10-2018, 10:07 AM   #7
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Re: R value


CertainTeed R21 ... I don't think its condensed
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