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Old 03-22-2019, 01:20 PM   #31
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Re: Insulation needs


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Originally Posted by Nealtw View Post
The R-value of anything only counts if the space is full and fit good, I think most people find rock wool better as it is harder to cheat than with fibreglass. So mostly it is just a matter of craftsmanship.
I think Bud's point was adding the foam and 1x2 or 1x3 has very little benefit over just adding a 2x2.
I have never worked with rock wool before---when I looked on the website that has it for sale and where I planning on buying it, it lists as 5.5" thick. Was thinking--a 2x4 is 3.5 inches plus the 1" foam plus the 1x3 of .75", that only adds to 5.25".


So, is rock wool "squishy" enough to fit my space given that it is only 5.25" and not the 5.5" thickness that the rock wool comes as?
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Old 03-22-2019, 01:30 PM   #32
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Re: Insulation needs


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Originally Posted by jsmith1107 View Post
I have never worked with rock wool before---when I looked on the website that has it for sale and where I planning on buying it, it lists as 5.5" thick. Was thinking--a 2x4 is 3.5 inches plus the 1" foam plus the 1x3 of .75", that only adds to 5.25".


So, is rock wool "squishy" enough to fit my space given that it is only 5.25" and not the 5.5" thickness that the rock wool comes as?

I am not sure but I think you end up with the R value of the 5.25 which would be the same as if you could buy a 5.25 thickness.
But you could go the thicker foam strip.
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Old 03-22-2019, 01:59 PM   #33
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Re: Insulation needs


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Sorry, you did 3/4 foam on the inside or outside? Can you explain what you mean by doing a flash and fill with closed cell foam followed by fiberglass?


I am buying my insulation at Menards--that's where I got the pricing on it.


Thanks
we did 3/4 foam on the outside.
see link below for flash and fill, basically flash 2" or so of spray foam, then fill the rest of teh space with fiberglass
https://www.buildingscience.com/docu...l-construction


FYI, mineral wool comes in 3.5" deep too.

I see the pricing at Mernards, makes sense, its for less coverage than I was getting per pack.
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Old 03-22-2019, 02:41 PM   #34
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Re: Insulation needs


You could buy 1.5" rigid and cut 1.25" strips so the 3/4 would bring you out to the 5.5" depth to match the 5.5" mineral wool.

As for fitting the 5.5" batts into a 5.25" space very easy, they come all squished in that bundle. The difference in r-value would be 5.25 divided by 5.5 or 95% of rated value. If that rated value is r-23 then you end up with r-22.

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Old 03-22-2019, 04:12 PM   #35
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Re: Insulation needs


Thanks a lot---I will do that I think.


Would it hurt if I put 1.5" foam behind and then I would have like a 1/4" gap? Does the gap hurt anything?

Last edited by jsmith1107; 03-22-2019 at 04:35 PM.
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Old 03-22-2019, 05:10 PM   #36
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Re: Insulation needs


Personally I would avoid the gap if possible, but doubt it would make any difference.

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Old 03-28-2019, 01:32 PM   #37
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Re: Insulation needs


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For caulking I use the large tubes of construction adhesive. Less expensive and will last forever.

Bud

Construction adhesive can be used instead of caulk?
I never considered that ...
Is it done often, do they have different colors like caulk?
Is it used around windows too?
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Old 03-28-2019, 02:49 PM   #38
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Re: Insulation needs


I use it strictly in the framing areas. If it will be exposed then use a caulk which would give you color options and paitable. I'm just a penny pincher and usually have the construction adhesive around.

Bud
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