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I am building a deck. One section of the deck will come out from the house 4 feet furhter than the rest of the deck. This pushes my joist spans to the next larger size. This part of the deck is supported from a beam a little further out, and the rest of the deck is supported from a different beam. Can I (and is it a good idea) to use 2x12 joists for the longer joists, and 2x10 joists for the shorter ones. I can raise the beam the 2x10s sit on by 2 inches so that the top of the joists are at the same level.

Or I can just buy all 2x12 joists for the whole thing.

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  • One of the reasons I wanted to use the 2x10s is to have a couple extra inches of clearance under the deck on that side. I am using Trex decking which allows for 16in joist spacing, but read 12 in joist spacing would give it a more rigid feel.
    – Michael
    Aug 16, 2013 at 12:32

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It is ok to use all 2x12's of course, and ok to use 2x10 joists on a 2x12 band.

Other ideas ...

1) use lower grade 2x12s in place of the 2x10s

2) use all 2x10s placing them 16" on center for the short spans and 12"oc for the long spans

3) look into cantilevering the joists on the long span, which may allow using 2x10s @ 16"oc (instead of uncantilevered 2x12 @ 16"oc).

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  • I can't find a chart for joist spans that is dependent on grade with a cantilever. I can find this one: southernpine.com/pdf/tables/SPtable12_060113.pdf but I don't know how to interpret that for cantilevers. It also doesn't match up exactly with the deck guide chart which has both cantilevered and not but just mentions visually graded.
    – Michael
    Aug 16, 2013 at 12:27
  • I'm not fond of trex, but that's just my personal preferences. An old-school solid feel will require over building in general, along with short spans (more posts). You can get about 2' more span by switching from 16"oc to 12"oc, or by cantilevering by 2ft. And you can get about 1' more span by up-ing the grade by 1. What are the lengths of the long and short joists? how much latitude do you have in locating the support beam?
    – mike
    Aug 16, 2013 at 19:44

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