Joist and Beam size for ground clearance


Old 05-20-14, 01:03 PM
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Joist and Beam size for ground clearance

I am rebuilding a deck in my backyard. The old deck had PT decking and I'd like to use Trex Transcends. The frame was not built properly so I decided to rip it down and am rebuilding it to make it stronger. Here is my plan:

The deck is about 32' along the house and 15' deep with angled corners on the far two sides, kind like half of a pentagon.

The original deck was only 24" off the ground which was even with two patio doors so there's no option to go higher. Not to mention, there is negative grading in the back of the house so I'm having 10 yards of dirt brought in to correct that. So the clearance from the ground is making it tight to fit post bases, posts, beams, and joists. Figuring I use 2x10 joists and beams, that leaves very little clearance if any. I'm using 10" sonotubes with anchor bolts, Simpson 4x6 post base, and a notched 4x6 post bolting to the beam. I'm thinking that I could save some inches using 2x8 joists and beams or at least replacing either the joists or the beams with 2x8. Any thoughts on this?

I'm making this deck freestanding (yet right against the house) with 3 full beams across (for a 15' deck) with joists 12" on center.
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Old 05-20-14, 02:52 PM
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It's impossible to comment on the beam & joist sizes without knowing the span lengths. There are numerous span tables available online that you can consult and see if going down to 2x8 is an option. I'd stick with the 2x10s though considering the size of the deck and the smaller size lumber would only gain you two inches.
Old 05-20-14, 03:41 PM
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The more shallow the member (joist or beam), the more deflection your deck will have. Moreso if you plan on large parties, with lots of heavy people attending. I'd be inclined to go with 2 x 8 joists and doubled or tripled 2 x 10s for the beams. Don't overspan the beams by spacing your columns/footings too far apart. If vertical clearance is a problem, an option to consider would be to eliminate the columns entirely, and just bolt the built-up beams to your anchor brackets embedded directly in the tops of the footings.

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