Deck Posts


Old 08-11-11, 07:30 AM
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Deck Posts

I am planning to build a deck. Deck size is 20 ft long, 12 ft wide and 8 ft high. How many posts will be require for a 20 ft long deck
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Old 08-11-11, 07:47 AM
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The post spacing will depend on your design. You can space them further apart if you use larger beams & joists. Smaller beams & joists will require the posts to be closer together. At 8ft high you should also look at larger than 4x4 posts and/or cross bracing to prevent it from swaying as people walk around on the deck.

With southern pine 2x6 joists 16" on center the maximum span would be 9'9". If you go up to 2x8's you can span up to 12'10" though I never like to go to the maximum allowable since the deck can have a soft bouncy feel. You can also increase the span length by putting your joists on 12" centers.
Old 08-11-11, 11:09 AM
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At that height if you are tying it into the house structure with a ledger board there are some places I know of that now are looking for adding jack post support under the ledger in case it some how came detached from the house regardless of what fastener methods are used. Probably not a bad extra safety precaution to consider. Also I think that 6x6 has become pretty much the standard now for high deck posts. Makes sense to me.
Old 08-19-11, 11:04 AM
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Deck over a Patio

I am building a pool deck over my existing cement patio. Can I attach the posts to the existing cement or do I have to dig into it. I am planning on using pressure treated lumber.
Old 08-20-11, 02:30 AM
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Welcome to the forums.

Your deck needs footings under the posts. You'll have to cut the concrete slab to install those footings. Size and spacing of each member involved is determined by what it's supporting, so start at the top and work to the bottom.

Joist spacing is determined by the type of decking you'll be using. Joist span depends on the size and species of PT you'll be using and the joist spacing. Beam size and spacing depends on species of wood and the joist span. Post spacing depends on the species and size of the beams. Footing size depends on the post size and spacing. Wind and snow load are also factored into each step. Seismic zone and frost have to be taken into account as well.
Old 08-20-11, 03:50 AM
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And to further Mike's comments, it will all be spelled out to you when you apply for your permit. Most items he mentioned will be local code items, such as depth of footings, size of lumber, etc.

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