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# Weight bearing capacity of flat roof

#1
10-19-12, 12:22 PM
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Join Date: Apr 2007
Location: California
Posts: 98
Weight bearing capacity of flat roof

Is it possible to estimate the weight bearing capacity of the following flat (7% slope) roof? The room below is open beam.

2" x 6" T & G Western Red Cedar or Douglas Fir over 4" x 10" x 18' beams at 5' OC. Room size is 18' x 30'

Thanks

#2
10-19-12, 12:33 PM
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Join Date: Oct 2004
Location: WI/MN
Posts: 18,657
So the 4x10" beams are at 5' OC?

What's the spacing of the 2x6s?

#3
10-19-12, 12:58 PM
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Join Date: Apr 2007
Location: California
Posts: 98
The 4 x 10 beams are 5' OC.

The 2 x 6 T&G is flat on top of the 4 x 10 beams There is no spacing between the 2 x 6 material.

#4
10-19-12, 01:00 PM
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Join Date: Oct 2004
Location: WI/MN
Posts: 18,657
Duh, you said T & G....

#5
10-23-12, 12:48 PM
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Join Date: Oct 2011
Location: USA
Posts: 3,196
Play it safe, and pay an engineer (licensed P.E. in your state) to run the calculations for you. You haven't provided enough information to accurately determine capacity, such as what the beams are composed of, or what the roof sealing surface is composed of.

#6
10-24-12, 02:59 PM
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Join Date: Apr 2007
Location: California
Posts: 98
I would hire an engineer if I was adding solar panels or equipment to the roof. I'm tearing off 3 rock roofs and adding 1 new one with 1/4" MLV for sound attenuation. The 3 old roofs probably weigh 10 psf. I'll keep my new assembly to 10 psf or less.

#7
10-24-12, 06:22 PM
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Join Date: Oct 2011
Location: USA
Posts: 3,196
Since the roof you're adding is likely to be less weight than the 3 layers you're removing (presuming the MLV weighs less than 2 layers of rock), exactly why did you ask the question in the first place?

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