I’m going to build a simple 12 x 12′ pressure-treated deck for the backyard. Want it to sit as close to the ground as possible. What would be the minimum number of concrete piers I could get away with? I’m thinking 9 (3 front, 3 middle, 3 back). But because I want it close to the ground, do I need piers at all? Could I rest the deck itself on concrete blocks on the ground (assuming that all these blocks would be perfectly level and sitting about 3″ off the dirt. Advice?
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I've seen decks on blocks, but I don't care for the looks, and unless you're planning on a big reveal around the outside...your layout has to be perfect.
Besides, I think it's far easier to level/layout 9 piers than 40something blocks(including a center support).
Also, I would think being up on piers would allow better airflow around/through the deck to dry out after rains.
The deck is gonna need maintenance every few years at least. Use pavers. With the right color and pattern it could be awesome.
9 piers laid out as you described, below the frost line. Blocks just set on the ground are going to shift around and settle unevenly, especially during winter frost heave.
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You could go with 6 sonos, and just sit triple beams on 6x6 galv. post holders set in the concrete.. Joist hang 2x10s and you would only be a few inches off the ground.
The recommendation from wood scientists is that even with PT, you build allowing 18" clearance for ventilation.
There are other scuzzy things that can grow there other than rotting wood.
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I'd lay it on grade.
Bob's next test date: 12/10/07
I did a roughly 8x14' "palletized" deck last year. Had the topsoil removed and graded the subsoil for good drainage away from the house. Put down about 8 inches of 3/4" stone, compacted only with the loader bucket. Then built a 2x6 PT frame and joists (16" OC), filled between the joists with more 3/4" stone, then screwed down 5/4 PT decking. After one winter, it still looks great and feels solid.
If you did use piers, i think only 6 would be required - 3 along each sides supporting a beam consisting of double 2x12, and then 2x10 joists between the beams.
I don't mean to be the party pooper, but you didn't say if you live where it freeze or not, not did you describe the soil. You can't get a reliable answer until that info is known.
In Hawaii, we use 16" pier blocks on compacted 3/4"- base coarse. There's also a minimum of 6" between wood and the ground for termite and rot.
In Colorado, those nine piers 10" in diameter would be good for all but the really shifty soil assuming they are at least 30" below the ground.
Hey!
The shifty soil is in Las Vegas. We got shifting soil here.