Attic Knee Wall Insulation

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Old 01-13-21, 10:38 AM
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Attic Knee Wall Insulation

Hi all. I'm finishing my partly unfinished attic, has HVAC and electrical, just needs insulation and drywall. I currently have 2x4 studs along the knee wall but was told by an insulation contractor that R21 was best for the walls and that I should replace the 2x4s with 2x6s which would accept the R21 insulation. My question is why replace the 2x4s? If I use craft faced insulation, which would get stapled to the studs, why would it matter if the insulation extended past the studs into the cavity behind it? I will be putting vents in the roof rafters and installing R30 there and R49 along the cross rafters (leaving a cavity between the ceiling and the ridge) to allow for proper air flow from soffit vents to ridge vents. Appreciated input on the knee wall conundrum.
 
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Old 01-13-21, 11:18 AM
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insulation extended past the studs into the cavity behind it
I have done that. The only downside is that the insulation may not expand sideways enough to fill the gap created by the 2X4. However the density of the wood stud should prevent any significant heat loss.
 
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Old 01-13-21, 12:13 PM
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A wall is a wall even if it's a knee wall.

Heat transfer goes up, out, then down, that's the order of insulating efficiency.

You are not going to gain much from that level of insulation on the knee wall, but then again it's not going to hurt anything.
 
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Old 01-14-21, 06:40 AM
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Thanks for the input. that was my thought as well, and the cost of 2x4s vs 2x6s is pretty significant for my project, would have been more than double the cost if i did it that way.
 
 

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