2x6 or 2x8 for deck joist

amakarevic

my deck will be about 7x10', which size joists should i use ?

Daniel Holzman

You don't state where you are located. The required joist size will probably be listed in the building code for your area. Best way to start is by discussing the deck design with your local code enforcement official. When I did my deck, the building inspector furnished me with a 20 page guide called "Design for Code Acceptance" that layed out all the rules for the deck, including beam and joist size, spacing, posts, bracing, stairs etc.

If you live in an area with no building codes, you may want to follow the International Residential Code anyway. The documents supporting the IRC tell you everything you need to know about sizing structural elements on your deck.

tcleve4911

Unless there is some other issue, just get 2x8's and sleep good at night.

Rule of thumb
1" of dimension to 1 foot of span.

i.e
6' span = 2x6
8' span = 2x8
etc
so if you have 7'.....round up...you're good to go

jlhaslip

agreed, but I never use anything under 2 x 8.

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Daniel Holzman

I strongly recommend you refer to code for your area. For example, my local code (IRC) specifies that the maximum allowable span for a 2x8 joist depends on the spacing of the joists (which you did not mention in your post), and the species of wood (which you did not mention in your post). IRC in the most restrictive condition allows a maximum span of 8'4" for a 2x8 joist made of redwood, western cedar, ponderosa pine, or red pine. Since you did not mention which way you were going to run the joists, if you need a 10 foot span you would need either a 2x8 or a 2x10, depending on the species of lumber you use.

Of course, you may be subject to a different code, if so your allowable spans could be different.

Gary in WA

As Daniel said: http://www.lancova.com/deckinfo.pdf
2009 up-date: http://www.awc.org/Publications/DCA/...eckarticle.pdf

Gary

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