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flyinghigh
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Converting Rafter / Joist Combinations into Squre Feet

08/17/2008 8:03 AM

Is there an on-line table that converts rafter/joist combinations into #/sf? For example, a roof with 2x6's 12"oc would contribute 2.65#/sf, at 24"oc, 1.33#/sf; while 2x8's 12"oc would contribute 3.53#/sf, etc?
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ba/ael
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#1

Re: Converting Rafter / Joist Combinations into Square Feet

08/17/2008 10:28 AM

Probably, but I couldn't find it. It will depend on the density of the wood too. Taking wood at 35 pounds per cubic foot, the weight of joists per square foot of floor will be 35*b*d*sp/1728 or near enough to 0.02*b*d*sp where b, d and sp respectively are width, depth and spacing in inches.

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ba/ael
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#2
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Re: Converting Rafter / Joist Combinations into Square Feet

08/17/2008 11:04 AM

Oops...I made a mistake. That should have been 35*b*d/(12*sp) or conservatively 3*b*d/sp. Sorry about that!

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flyinghigh
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#3
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Re: Converting Rafter / Joist Combinations into Square Feet

08/17/2008 8:43 PM

Bruce, thx. I looked up in engineeringtoolbox.com the density of DF. Using their 33#/cf and your suggestions, I came up with #/sf=((33#/cf)*b*d*12/1728)/(xft oc*1ft), or (0.229*b*d)/xft oc. It seems to check out ok.
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Rotag1
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Re: Converting Rafter / Joist Combinations into Squre Feet

08/18/2008 5:08 AM

Boise Cascade has calculation software that may be of help with this and may other projects. http://www.bc.com/wood/ewp/software.html
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