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Davengerguy 10-30-2012 11:23 AM

Max span for 2 2x8 for a deck
Needing to span 14' 3" for a deck at 12 on center. Don't have room for 2x10 and a single 2x8 spans 13' 8" Wanting to know if 2 2x8 still spaced at 12 on center would be safe for wet service with 40 psf live load 10psf deal load?

and if it is ok, what would be the max load on it.

hand drive 10-30-2012 11:26 AM

Davengerguy 10-30-2012 11:45 AM

thanks for the info, but I still do not see a max span for 2 2x8 used as a floor joist. I see one listed for a beam, but not a floor joist.

hand drive 10-30-2012 01:09 PM

you are getting into specialized framing that is not listed in code books, it seems that if your single 2x8 span calc is a few inches short then sistering a joist on will increase span capacity and be ok.

GBrackins 10-30-2012 01:22 PM

what grade and species of wood are you using? is it preservative treated (at mill)?

woodworkbykirk 10-30-2012 01:26 PM

or add a second beam mid span

Davengerguy 10-30-2012 02:58 PM

It is treated wood.
Grade is No2
I am not with the lumber right now but I belive it is Yellow pine.

GBrackins 10-30-2012 04:15 PM

using doubled 2x8 pressure treated #2 southern pine at 12" o.c. will provide you around L/600 live load deflection which will exceed the 2009 International Residential Code requirement of L/360.

here is the wet service span chart of southern pine joists. if you wanted you could order machine stress rated lumber and be in compliance with 2x8 #2 at 12" o.c.

the issue may be your building inspector. there are no span tables I am aware of that provide for double floor joists in a wet service condition. the inspector would be within their right to require a sign off from a professional engineer to demonstrate compliance with the code requirements.

Good luck!

GBrackins 10-30-2012 06:06 PM

you could also configure your deck into a free standing deck as outline in the American Wood Council's "Prescriptive Residential Wood Deck Construction Guide" as linked by harddrive above.

this would reduce your joist spans

another option .....

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