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Discussion Starter · #1 ·
I could use a little help, guys. I'm finally getting around to replacing the insulation in the coldest bedroom of our house. I opened it up and, wow, I should have done this 10 years ago. Settled insulation and bare areas everywhere. 2x4 cavity.

Can I add a layer of extruded before the pink, like in a basement, or does that cause a double vapor barrier problem? Pink will be faced on the interior side. Exterior has vinyl siding and wrap, that's it. Thanks much.

Nice how the window guys didn't insulate around the frame, either....grrr..
 

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Sean
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Yes (& I am assuming XPS?) the catch is compressing the batt reduces its efficiency & is against the manufacturers instructions. You can consider filling the whole cavity with foam boards or use blow FG or cellulose in there. Personally I would just go with foam board cutting it a little narrower and use spray foam to seal around the edges
 

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Discussion Starter · #3 ·
Yes (& I am assuming XPS?) the catch is compressing the batt reduces its efficiency & is against the manufacturers instructions. You can consider filling the whole cavity with foam boards or use blow FG or cellulose in there. Personally I would just go with foam board cutting it a little narrower and use spray foam to seal around the edges
Ok, thanks. Yes, I did mean XPS. I figured some 3/4 thick might help since the sheathing is 1x boards instead of ply sheets.
 

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diplomat
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Actually batts have a higher r value per inch when compressed up to a point. This is why r15 weighs so much more than r11. I think it's Owens Corning who publishes a chart about compressed r values. They are of course lower overall but higher per inch. You could do r15 and then 1/2" polyisocyanurate and screw the new drywall through, to achieve some thermal break plus about r19 overall
 

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Sean
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Love that line - the fact is they have to double the density / amount to get an additional R Value & trying that with batts is pretty foolhardy especially as most installs are done wrong - R9 to 11 to 13 to 15 - yep double, double, double
No voids, compressions, etc... to get the rating listed per the manufacturer
 

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Discussion Starter · #6 ·
Since it's less than 80 s.f. with oddball cavity dimensions, maybe I'll just install a double layer of XPS and spray foam the edges. Any reason not to do so? This side of the house is southern exposed and gets baked, as well as the most direct storm winds.
 

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Sean
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Since it's less than 80 s.f. with oddball cavity dimensions, maybe I'll just install a double layer of XPS and spray foam the edges. Any reason not to do so? This side of the house is southern exposed and gets baked, as well as the most direct storm winds.
Ill refer you back to my original - that's fine but make sure you fill the cavity to keep any separation from opening up or attach the foam together as you go & make sure it sits flush with the exterior - some foams allow that, adhesives, or specialty connectors
 
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