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2x10 alternative for framing


Northern Mike's Avatar
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04-16-13, 03:59 AM   #1  
2x10 alternative for framing

So I am going to be expanding and reinsulating our third floor room (attic room) this summer. The existing room has very poor insulation as is, and with the attic containing floor boards throughout, we figured, why not.

Here is the issue.
I'm looking at going over kill on the wall insulation and using an R-40 batt (or better if I can find it). The issue is it's going to require 2x10 studs to as the insulation is 9.5" thick. This is going to make supporting this insulation very expensive and add a lot of weight (I need to carry these boards 3 flights of stairs).
Is there an alternative to using 2x10 studs that would be acceptable, or am I going to kill a whole forest just to hold my insulation in place?


I'm gaining about 600sqft and increasing the R value of that room from ~R-2 to ~R-40.
Local code is now R-24 to R-29 for exterior walls.

 
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04-16-13, 04:11 AM   #2  
2x12 alternative for framing.

A quick correction, the insulation is 11" thick. This means 2"x12"

 
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04-16-13, 05:34 AM   #3  
Hi Mike,
When a wall gets that thick it is better to build two 2 x 4 walls. Space the walls 5.5" apart and install 6" Roxul between them and fill each (2 x 4) side with 3.5" Roxul. R-15 for each of the 3.5" cavities and R-20 for the 5.5" space will get you over R-50. It also reduces any thermal bridging. 2 x 4's are also easier to carry .

Bud
That would actually save tons of $$.
I also wondered the value of going high R value with the thermal bridge of the wood.

 
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04-16-13, 05:57 AM   #4  
Hi Mike,
When a wall gets that thick it is better to build two 2 x 4 walls. Space the walls 5.5" apart and install 6" Roxul between them and fill each (2 x 4) side with 3.5" Roxul. R-15 for each of the 3.5" cavities and R-20 for the 5.5" space will get you over R-50. It also reduces any thermal bridging. 2 x 4's are also easier to carry .

Bud

 
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04-16-13, 06:33 AM   #5  
That was my initial thought as well, but had not done it, so was interested in seeing an expert response. The only question that I would have then would be the weight of two of the walls not resting on joists. Two of them would obviously rest across the joists, but the other two would be resting mid-span on the subfloor. Is blocking then required, or is this a non-issue since the weight of the structure would remain on the outsdie walls? Not trying to mess up your thought Mike, nor question your judgement Bud; just curious.

 
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04-16-13, 06:59 AM   #6  
That was my initial thought as well, but had not done it, so was interested in seeing an expert response. The only question that I would have then would be the weight of two of the walls not resting on joists. Two of them would obviously rest across the joists, but the other two would be resting mid-span on the subfloor. Is blocking then required, or is this a non-issue since the weight of the structure would remain on the outsdie walls? Not trying to mess up your thought Mike, nor question your judgement Bud; just curious.
You'r questions are valid.
I was thinking of using a 2x12 kickplate (bottom plate) at the bottom. This would make it much easier to keep everything together and inline. The wall would be non-load bearing as it's in the attic and not replacing any existing supports within the attic.

Long story short, the walls for this attic room should be considered interior/non-load bearing, just need to accommidate a ton of insulation.

 
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04-16-13, 08:34 AM   #7  
The floor boards are the original 1"x8" (need to confirm) planks that are used as the subfloor on all levels of the house. It supports my weight walking on it with no noticeable give, so I don't think there should be an issue with supporting the walls that will span multiple joists.

The attic arrangement as it stands now has made it tough to estimate current R values. There is blow in insulation between the floor boards and the ceiling (of the second floor), and then another ~4 inches of blowin on top.

 
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04-16-13, 09:24 AM   #8  
pedro, you point is correct and if one half of that double wall is to be resting on the subfloor only, then some extra bracing would be advisable, depending upon what that subfloor is. I actually have some 35 year old structure in my current house where cross support should have been used and the floor distortion is very noticeable. Just using a single bottom plate of 2 x 12 would help, but a support underneath or a couple of 2 x 12 studs as part of the wall would as well.

The 11.5" wall would be a tight fit for the 12.5 inches of Roxul, but a hand saw can shave off a bit if needed. It may compress enough, I just have never tried to compress the Roxul. You would need something behind it to push against.

As for overkill, remember it is far less effective if there are areas which fall short of the higher value. Neatness counts.

Bud

 
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