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Old 02-11-2012, 06:03 PM   #1
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Furring out existing 2x6 rafters


My house was built in 1941. It's 1.5 story with regular gable roof. We are planning on renovating our 2nd floor. I have few questions about the approach i have chosen.




Existing rafters are 2x6 and 15' in length, span is 14'' o.c. The floor joists are 2x8 and joined from two pieces in the middle (each joist basically consists of two pieces). They are 12' in length (each, making total length of a bit less then 24'' because they overlap like 5''). I attached the picture. There are 2x4 collars nailed every other rafter.

I am planning on furring out rafters and ridge board with 2x4 douglas firs, creating an air channel (smth like 1'' from sheathing) along the space between rafters by using plywood wrapped in radiant barrier foil (exterior side), then putting unfaced R-30 insulation and plastic sheeting for for vapor barrier.

I will use simpson hardware. 3x7, 16ga plates for rafters, 6x2 12ga angles for reinforcing rafters to the ridge board, 9x1.5 16ga angles for reinforcing rafters to the floor joists.

Then, since i am adding weight to the rafters, i am planning to reinforce floor joists in the place where they connect together in the middle. I am thinking of using some simpsons plates and corners, and/or bolting them together.

I will be putting new subfloor using 4x8 boards, and then nailing hardwood floor. Also plan to add some knee wall cabinets.

Here are the questions:

1). By furring out rafters I will add weight to the roof structure (wood + metal plates & corners + plywood). Does this pose any structural problems? Should I reinforce the floor joists better (extend it with 2x4, etc.) then with just some hardware metal plates and bolts?

2). By removing collar beams I potentially increasing outward thrust, however, i don't think that those are helping much. The floor joists is really holding those rafters together. Therefore I plan to reinforce those joists. Question is: from what i described above , does it sound reasonable?

Thanks


Last edited by kirylm; 02-11-2012 at 06:12 PM.
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Old 02-11-2012, 06:17 PM   #2
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Furring out existing 2x6 rafters


I'm missing something, is your plan to take out that center supporting wall and the ceiling rafters to make a catheral celing?

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Old 02-11-2012, 06:20 PM   #3
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Furring out existing 2x6 rafters


no, no cathedral ceiling, i am keeping the floor. the picture's dimensions is not exactly correct, the height (from the ridge to the floor) is about 10'.
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Old 02-11-2012, 06:22 PM   #4
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Furring out existing 2x6 rafters


Looks like an attic not added living space.
How far is it from the tops of those rafters to the center of the ridge beam?
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Old 02-11-2012, 06:23 PM   #5
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Furring out existing 2x6 rafters


right, its an attic, but its finished to add living space.
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Old 02-11-2012, 06:27 PM   #6
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Originally Posted by joecaption View Post
Looks like an attic not added living space.
How far is it from the tops of those rafters to the center of the ridge beam?
if i understand correctly, you are asking about the height in the middle from where rafters intersect with ridge board to the floor joists? then - its about 10 feet.
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Old 02-11-2012, 08:33 PM   #7
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Furring out existing 2x6 rafters


Quote:
Originally Posted by joecaption View Post
I'm missing something, is your plan to take out that center supporting wall and the ceiling rafters to make a catheral celing?
Joe,

You mean ceiling joists....right?
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Old 02-11-2012, 08:35 PM   #8
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Furring out existing 2x6 rafters


I am not removing ceiling joists
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Old 02-11-2012, 09:11 PM   #9
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Furring out existing 2x6 rafters


"long the space between rafters by using plywood wrapped in radiant barrier foil (exterior side), then putting unfaced R-30 insulation and plastic sheeting for for vapor barrier"
Why are you placing a vapor barrier in? you don't need it in the attic except were the ceiling is and that is were the Kraft paper needs to be face down towards the living space. doing it from what you described sounds like your going to trap moisture.
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Old 02-11-2012, 09:14 PM   #10
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Furring out existing 2x6 rafters


right, the ceiling will be right on the rafters. i will be putting drywall on top of that plastic vapor barrier, so it will be facing living area.
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Old 02-11-2012, 09:34 PM   #11
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Furring out existing 2x6 rafters


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Originally Posted by kirylm View Post
right, the ceiling will be right on the rafters. i will be putting drywall on top of that plastic vapor barrier, so it will be facing living area.
Don't just use the Kraft faced batts it is a whole lot better. the Plastic is how can I say like placing your head is plastic bag and expecting to breath fresh air! if you do that you get water vapor on the plastic and in contact with the sheet rock and then you get mold. and damp sheet rock and more problems. I just wish who ever came up with placing plastic sheathing over insulation would be around to to repair the moisture damage it causes.

Last edited by Nailbags; 02-11-2012 at 09:38 PM.
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Old 02-11-2012, 09:36 PM   #12
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Quote:
Don't just use the Kraft faced batts it is a whole lot better. the Plastic is how can I say like placing your head is plastic bag and expecting to breath fresh air!
thanks for the advice

still my other questions are unanswered
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Old 02-11-2012, 09:42 PM   #13
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Furring out existing 2x6 rafters


your floor joists are 2x8 correct? can you read a lumber stamp? if you can can you tell me what kind of lumber it is? is it Doug fir larch? or Doug fir?
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Old 02-11-2012, 09:43 PM   #14
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Furring out existing 2x6 rafters


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Originally Posted by Nailbags View Post
your floor joists are 2x8 correct? can you read a lumber stamp? if you can can you tell me what kind of lumber it is? is it Doug fir larch? or Doug fir?
hmm.. i doubt that I will get that, but i will definitely try. does it matter that much?
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Old 02-11-2012, 09:48 PM   #15
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Furring out existing 2x6 rafters


yes it does I can give the formula for the tinsel strength of each types of wood and how much they can hold. Doug Fir Larch is the strongest, then Doug fir then Hem Fir then southern white pine then yellow pine the weakest.

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