Deck Joists Questions on Free Standing Deck Over Concrete Patio

My deck is 12' wide. What size lumber 2x8, or 2x10 to use for joists? Also it is 7' above ground on a concrete patio free standing or floating. Can I use metal plates for 2x4s fastened to the concrete?

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Mar 19, 2010
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Joist Span Comments
by: Editor - Rich Bergman

I have just redone our joist span table which I think will help you out a lot.

As far as your question about securing 2x4s to a concrete surface I am not sure I understand your question.

You can certainly secure support posts to concrete. But you have to determine between using 4x4 or 6x6 posts. I don't have a definitive answer for you on that one but my first inclination is to use a 6x6 over a 4x4 post as you are starting to get up fairly high.

You will find that 6x6 support posts are less likely to wobble but you would probably have to add supporting cross members joining the support posts to provide sufficient stiffness.

If your posts are not pressure treated and the ends are not coated in appropriate preservative then the building code will stipulate that your posts be elevated a minimum of 1" above the surface.

But go to this page to see the span tables.
https://www.decksgo.com/deck_joist_span.html

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