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Load carrying capacity of 2X4 Framing of Attic Floor

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  #1  
Old 06-06-07, 10:04 PM
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Join Date: Oct 2004
Location: USA
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Load carrying capacity of 2X4 Framing of Attic Floor

The question of the load carrying capacity of the framing on a project I am working on came up in my post to a different forum.

I am working on a 1910 era Craftsman style house. I am cleaning the attic, eliminating the knob and tube electric and re-insulating.

I would like to have dead storage up there (you really can’t stand – max head room is probably 5 feet under the peak) and was thinking of adding ¾ inch plywood screwed to the 2X4 joists.

The joist construction is 2X4 with 16 inch spacing and lath and plaster on the underside. The longest run between a load carrying wall is probably 10/11 feet.

From a practical point of view can the structure withstand the weight of the plywood and storage? What would be the live/dead load limits? Are there some simple solution that could be designed that would strengthen the assembly without compromising the space?

Thanks,
David
 
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  #2  
Old 06-07-07, 01:31 PM
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Join Date: Jan 2007
Location: Central Indiana
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What are the live/dead load limits on a 2x4 joist structure? -
2x4 on 16" centers, asuming E = 1.2x10^6 (SPF of today), 10'3" span, L/240 deflection, allowable loading = 10 psf live/5psf dead load. In other words, you can't (or shouldn't) use it this way for storage.

2x6's alone would up this to over 20 psflive/10 psf dead. My suggestion - sister 10' 2x6's to the existing 2x4's with an air nailer, this would up the capacity even more.
 
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