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Old 03-22-2013, 04:11 PM   #1
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Furring out 2x6 trusses


I'm looking into finishing a room above my attached garage and am running into a problem with the insulation. The roof is supported by trusses and the boards going to the peak are made with 2x6s. A portion of the roof would serve as a sloped wall for the room. I'm trying to figure out a way of getting R38 insulation in a 5 1/2" bay. I've read that closed cell foam would be able to do it but that much CCF is very expensive.

Would furring out the existing 2x6s with a second 2x6 be too weak? If I fastened it with construction adhesive, screws, and plywood bracing, would it be sturdy enough to hold the drywall? This wouldn't be structural for the roof, it would only be used to give enough room between the roof and drywall for enough insulation. I've seen people use 2x2 strapping to do this but never 2x6, wondering if it would be dangerous or against code.

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Old 03-22-2013, 04:31 PM   #2
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Furring out 2x6 trusses


Got a picture?
Where these trusses made to even hold the weight of a floor in a finished room?
What size is the bottom cord and what's the spacing and spans?

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Old 03-22-2013, 05:21 PM   #3
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Furring out 2x6 trusses


The space above the garage was built with the intention of finishing it at a later time. I believe the board at the bottom of the truss is a 2x10, 24' span spaced 24" on center. Given that the trusses have no center supports, I would say they were designed to support the floor of a room.


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Old 03-22-2013, 05:28 PM   #4
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Furring out 2x6 trusses


Now just go back and add your llocation to your profile.
Go to quick links to edit.
Any questions on insulation always depend on location.
Do not just mention it in a post!
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Old 03-22-2013, 07:08 PM   #5
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Furring out 2x6 trusses


I'm from Maine and the code for ceiling insulation is R38.
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Old 03-22-2013, 07:57 PM   #6
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Furring out 2x6 trusses


This is really more like a stick framed attic with collar beams and a knee wall. Do you know if the floor rating is 40PSF? Isocyanurate foam gives you about 6.5 per inch. To get R38 you need just about 6 inches, and you are going to need airflow over the top of the insulation, so I see your problem. You only need more depth at the sloped portion so frankly, I dont see why you cant either get a variance for just that area, and just use about 4 inches of iso there. That gives you R-24 which is really pretty darn good. If you buy it from a roofing supply, or even better yet, you can contact a commercial roofing contractor and see what he has "in the barn" left over from a large low slope project. I bet he will be happy to sell it to you at a really good price. You can buy two inch and double it, or any thickness at all and put in layers. You can use "Stuff " in the edge gaps, and Surform it off after it sets up. I havent tried it yet but I bet a Variable Speed muti-tool with a half moon fine toothed blade would cut it really nice.

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Old 03-23-2013, 09:13 AM   #7
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Furring out 2x6 trusses


What are your thoughts on securing another 2x6 to the existing 2x6 to make the cavity deeper? It gets pretty cold here in the winter so skimping on insulation wouldn't be my first choice. I've found some information on people furring out framing but most only do an inch or two. Furring out an additional 5 1/2 would allow for venting and a decent amount of insulation but I want to make sure it can support the weight of the drywall I'm eventually going to hang on it. My thoughts are to use construction adhesive, long screws, and some 1/2 plywood to span the gap between the two boards to make it sturdy. The cost of all that still seems to be cheaper than filling each bay with closed cell foam.
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Old 03-23-2013, 09:42 AM   #8
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Furring out 2x6 trusses


Doing what your suggesting will work.
Just do not use screws, use nails instead.
Whole lot faster with a nail gun, cheaper, and screws should not be side loaded like that.

I'd attach the plywood or OSB to one side of the 2 X 6's before installing, lift them in place, nail the sheathing on one side to hold them up and move on down the row.
Then go back when done and do the other side and add the other missing nails, using #8 ring shanked nails.
This way your not trying to hold up two pieces of material, line them up and nailing all at the same time.

You only need the baffels on the slooped part of the ceiling.
I'd be double checking those knee walls with a string before going to far.
Often times there not straight and will make the area between the ceiling and the wall wave.
Often times a layer of 1/2" foam is added to the inside wall and sheetrocked over it. I also often times add a layer or house wrap on the back side of the insulation to reduce wind wash.

Now would be a great time to add some storage area behind those knee wall.

Last edited by joecaption; 03-23-2013 at 09:48 AM.
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Old 03-23-2013, 09:56 AM   #9
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Thank you for the great suggestions.
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Old 03-23-2013, 10:07 AM   #10
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Furring out 2x6 trusses


That room looks like the twin to one I did here in VA.
We add storage for things like Christmas stuff in the walls.
Added two dormers to let in more light, 4 skylights.
Added walls to make bedrooms, added closits in the tallest part of the rooms so there would not be a slooped usless space.
Added HVAC, and a bathroom and sitting room down stairs.

It was a real challange, someone had installed all the water lines on outside walls, not one of the drains was in the right place, there was only one small window, 24" wide stairs when we started.
Down stairs the builder had 4 X 4's every 8' right in the middle of the room just nailed to the sides of the floor joist.
The plumber had just slide the roof flashing over the pipe with roofing tar on the roof and just face nailed it.
There was no cleanout for the drain line.
There was a GFI in every single outlet box.
And this was all new constrution.
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Old 03-23-2013, 11:43 AM   #11
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Furring out 2x6 trusses


Quote:
Originally Posted by skipdawgy2 View Post
I'm from Maine and the code for ceiling insulation is R38.
check with your building official. typically under the International Energy Conservation Code (not sure if that is applicable in Maine or not) you are allowed to reduce your required R-38 to R-30 for situations like this. You are allowed 500 s.f. of reduced R-value.
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Old 03-23-2013, 11:45 AM   #12
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Furring out 2x6 trusses


from the 2009 IECC

402.2 Specific insulation requirements (Prescriptive). 402.2.1 Ceilings with attic spaces. When Section 402.1.1 would require R-38 in the ceiling, R-30 shall be deemed to satisfy the requirement for R-38 wherever the full height of uncompressed R-30 insulation extends over the wall top plate at the eaves. Similarly, R-38 shall be deemed to satisfy the requirement for R-49 wherever the full height of uncompressed R-38 insulation extends over the wall top plate at the eaves. This reduction shall not apply to the U-factor alternative approach in Section 402.1.3 and the total UA alternative in Section 402.1.4.

402.2.2 Ceilings without attic spaces.
Where Section 402.1.1 would require insulation levels above R-30 and the design of the roof/ceiling assembly does not allow sufficient space for the required insulation, the minimum required insulation for such roof/ceiling assemblies shall be R-30. This reduction of insulation from the requirements of Section 402.1.1 shall be limited to 500 square feet (46 m2) or 20 percent of the total insulated ceiling area, whichever is less. This reduction shall not apply to the U-factor alternative approach in Section 402.1.3 and the total UA alternative in Section 402.1.4.

use closed cell in the clipped area of the roof/ceiling and other type in knee walls and flat ceiling area
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Old 03-23-2013, 12:20 PM   #13
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Furring out 2x6 trusses


As the "attic room" trusses are designed for living space, you should have no worries about adding some 2x to the rafters for furring. I built 6-8 rooms similar with the same span/cords for floor joists (over garages also) and it is a very stable/strong system.
I would first; string-line the knee walls/ceiling cords for plane (add shims of cardboard before drywall from box store), add gable end wall drywall backing, wire, etc., XPS vertically in floor cavities under the knee walls (appears f.g. already done?), frame attic accesses, ask your local AHJ (Maine has your own Codes/local amendments), housewrap the attic side of wall insulation (as said by Joe), some ideas on venting; http://www.buildingscience.com/docum...n-roof-venting

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