Why not bury deck posts?


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Old 04-05-07, 10:53 PM
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Question Why not bury deck posts?

I'm putting a deck on my house in a few weeks, and I have a question about deck posts. I know the general consensus is to use tubeforms and a metal bracket, and not to bury the posts. But, I hate the look of a concrete cylinder above ground, plus the deck will sit about 4' above grade in certain spots, so I'd like to provide some better lateral support for the posts. My thought is to dig the postholes about 42" deep, screw a couple of short 2x4s to either side of each post (forming a "t"), and drop the post in the hole so that the 2x4s rest on the ground and the post sits about 18" off the bottom of the hole. I would plumb and brace the posts to their final position, then fill the hole with concrete, to about 6-8" below grade, and backfill with dirt. Before I put the posts in the ground, I will coat the bottom of the post with a 2% copper preservative to prevent rot. To me, this provides a nice monolithic solution for footer and lateral support. Does anyone see a problem with doing this?
 
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Old 04-06-07, 05:03 AM
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Welcome to the forums! The main thing I can see a problem with is code. Check your area codes to see if they allow it to be done. In addition, the wood, being encased constantly in wet soil will rot, guaranteed, no matter how much surfactant treatment you put on it. The lateral support you need will be provided by the Simpson Strong Tie base supports that will be installed permanently to the top of the concrete. You don't have to bring the concrete tube so high as to be ugly, but just enough to keep the wood from ground contact.
 
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Old 04-06-07, 06:02 AM
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As Larry said, you need to check local codes to find out whether you can do this in the first place. If yes, then you can start worrying about whether you should.
 
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Old 04-06-07, 06:38 AM
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Looking down the road, there will come a day when the posts need to be replaced. This will be very difficult if they are buried in concrete.
 
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Old 04-06-07, 07:29 AM
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Much thanks for the quick responses, fellas. Our local code allows for buried posts, but doesn't necessarily say that you can bury them in concrete, which is why I wanted to see if anyone has ever tried my theory. I thought that if I coat the post where it contacts the ground, it prevents rot. If that is not the case, how can any P.T. lumber be rated for ground contact? In regards to using the Simpson base, I wouldn't have thought that it provides much lateral support, since you are just nailing the bottom couple inches of the post. Having said that, I'm still the novice, so I'll trust the more educated folks on this one, and I'll use the Simpson base above grade.
 
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Old 04-06-07, 07:44 AM
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Glad you are going to keep the posts above grade. Surrounding PT lumber with concrete is never a good idea - besides the ground moisture the concrete will attract and hold moisture. While not as stable a fence post buried in gravel or dirt will usually outlast one set in concrete.

PT wood will outlast untreated wood when subjected to moisture or insects but sooner or later it will detriate from one or the other.
 
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Old 04-06-07, 07:48 AM
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I have a 25 year old house with a large deck in the rear. Parts of the deck are 5' above grade. The deck is supported on 6X6 PT posts that are buried in the ground. They are buried to the frost line (48") and partially encased in concrete. They met code requirements at the time of construction.

Two years ago I expanded my deck. I used sonotubes to suport the new posts. I decided to redo all the posts this way because I was concerned the old posts would eventually rot. I dug around the first post and it was as solid as when it was first installed. No evidence of rot. I left the original posts as they were first built.

From time to time I read posts here that caution against using PT in contact with soil. I think it may depend on the area you live in. I have PT fence posts (18 years old) PT deck posts (25 years old), a 3' high PT retaining wall and PT ties around flower beds. None of this has shown any indication of rot. I think the jury is still out on the newer stuff.

I would ask around (building inspector, contractors) in your area to see how PT holds up. Just be aware that they don't make PT like they used to.
 
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Old 04-06-07, 08:02 AM
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Originally Posted by Wayne Mitchell View Post
From time to time I read posts here that caution against using PT in contact with soil. I think it may depend on the area you live in.

Very true!!!

When I lived in fla. I had both cedar and PT fence posts that had to be replaced within 10 yrs of installation. I have neighbors here in tenn. that have 10 yr old untreated fence posts that are still standing
 
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Old 04-06-07, 08:41 AM
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Why not bury deck posts?

You may not like the look of a couple of inches of concrete above ground, but you can always hid it with landscape rock.

The future owners of the house might like the look so they know it was done properly.

Most codes to not permit a deck attached to a house if it is supported by a temporary support like buried posts.

You propbably cannot buy posts equal to the old treated wood for buried use (high concentration of chromated copper arsenate). This is not the "good old days" of poison and old growth limber.

Good luck.

Dick
 
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Old 04-06-07, 09:40 AM
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Glad I joined this forum -- so many quick responses, and great points all around. Thanks to everyone's input, I'm increasingly convinced that it doesn't make sense to even risk the possibility of having the posts rot out. I'll keep them above grade and hide the pillars with mulch or landscape rock. Thanks again.
 
 

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