Deck posts–buried posts or concrete?
I posted a question yesterday as to the best way to dig post holes for a deck I am building. I received a dozen responses in less than twenty four hours; I just wanted to say thanks for the input, it’s very helpful in planning this project. I think I’ll go with the majority and rent the Dingo to dig the post holes and use screws instead of nails to fasten the deck. As you can probably tell from the title of this post, I have another question.
I will have about 12 vertical posts, (maybe more), that will support the deck. The holes will be at least 36″ deep. Because the ground slopes, the high side of the deck will be about 8 feet above grade. I haven’t decided what type of footer to use, I’m down to these two options:
1. An 8″ thick by 12″ diameter concrete base poured in the bottom of the hole. The post resting on top of the concrete and the rest of the hole backfilled with soil. With this idea I’d have about 30″ of the post buried in the soil. This seems cheap and fairly easy, but the post would be in contact with soil.
2. Either fill the hole with concrete, or put something like a Sonotube in the hole and fill that with concrete. Then I’d have 3 feet of solid concrete to put my post on and the wooden post would never touch the ground. This seems “better” in terms of keeping the wood away from the soil, but obviously more expensive since I would have to buy Sonotubes, metal post brackets, and more concrete.
Some people have told me the Sonotube route is a waste of money, others have said that even treated posts embedded in the ground will eventually rot and need replacement. The inspector says that either method is acceptable. I don’t want to waste money if I don’t have to, but I also don’t want to replace posts in the future if I can spend now and save later.
Any advice is appreciated, and thanks again to all the replies to my earlier post.
Replies
There are a few versions/ manufacturers of this available from your local lumber yard:
http://www.redibase-form.com/pages/info.html
or
http://www.soundfootings.com/SFresource.php
I googled "deck footing forms."
Wood, PT or not, should not be in contact with the ground, let alone buried in it.
Attach the posts to the piers using this:
http://www.strongtie.com/products/connectors/AB-ABA-ABE-ABU.asp
Also, this is a good resource:
http://www.strongtie.com/deckcenter/index.html?source=topnav
Take the course.
At the bottom of the page they list connection options.
I hope this helps.
Frankie
Flay your Suffolk bought-this-morning sole with organic hand-cracked pepper and blasted salt.
Thrill each side for four minutes at torchmark haut. Interrogate a lemon.
Embarrass any tough roots from the samphire. Then bamboozle till it's al dente with that certain je ne sais quoi.
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Wood, PT or not, should not be in contact with the ground, let alone buried in it.
Unless it is the type that is specified for use underground, such as the type used for permanent wood foundations. However, that is not the normal stuff you find at the lumberyard.
"Wood, PT or not, should not be in contact with the ground, let alone buried in it."hope that is just an opinion and not a rule the people with successful wood foundations should know about.FWIW, I removed some posts a few years ago from the end of a driveway where they had stood for about 12 years or so. This was the old CCA I presume. I didn't plant them.I did not see the slightest hint of decay beginning any place on them. Then I used them for a year as cribbing on the bottom of a pile.They still look almost new, except faded to grey.
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Okay, it's an opinion based on what I have seen and been taught. Your results my differ. That's cool.I've been taught by some pretty knowledgable folks, not to build wood structures with the wood coming into contact with the ground. Fences are a different story as are landscape retaining walls etc. Fence decays/ falls 10-15 years later, so what. We'll fix it next month. Retaining wall begins to fail. Okay, now we have a project for next summer. Deck post fails... ouch.Are there wood components which will work? Sure, but if, just if, the posts ever need to be replaced, it is so much easier to replace them from the top of a pier than 3' in the ground.Again, this is just my opinion.Frankie
Flay your Suffolk bought-this-morning sole with organic hand-cracked pepper and blasted salt.
Thrill each side for four minutes at torchmark haut. Interrogate a lemon.
Embarrass any tough roots from the samphire. Then bamboozle till it's al dente with that certain je ne sais quoi.
Arabella Weir as Minty Marchmont - Posh Nosh
It always depends on soil and ground water conditions for me, but a method I have used sometimes with success is this.
Dig four feet or more ( our frost depth is about 40-48 inches here)
Take a bag of Sakrete Concrete mix and lay it flat in the bottom of the hole.
Stand the 6x6 ground contact treated post on it with the portion buried in the ground wrapped with 1" blue foam and backfill.
The foam is because ice lens conditions can grab a textured or porous surface and freeze to it. jacking it out of the ground as the ice lens grows. It won't grab the foam
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Taunton University of Knowledge FHB Campus at Breaktime.
where ...
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Drill a hole in the bottom of the post and pound in a short piece of rebar. This pins the post to the concrete so it won't slide laterally.
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
"Take a bag of Sakrete Concrete mix and lay it flat in the bottom of the hole."
Are you saying you dump the concrete in without mixing it? If so, are you confident that the footer will be as strong as it needs to be?
Jon Blakemore RappahannockINC.com Fredericksburg, VA
What we did on our deck is to set and brace the posts (with rebar in the bottom) and then pour concrete until it was just flush with the bottom of the post.
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
By the time you set the post on the bag. it puckers down in a bit and that depression is going to resist lateral pressure.
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not there for strength, just for added compression resistance.A deck does not need that much 'strength' for footings. Lot get build just on posts or sonotubes with no foot and the more common problem here is frost jacking them out rather than any sinking in.'course that depends on how many and how often, soil type, ground water etc.
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The size of the footing (square inches) should be calculated (or pulled from a table) to balance the downward force on the post. For a simple deck the post may not need much footing (in most soils), but if the deck is covered/multilevel/whatever then a footing of 8-12 diameter inches may be required. The footing can simply be large (maybe 2") clean crushed rock piled as deep as the hole is round and compressed, though usually concrete is simpler, and doesn't need compressing.Around here "frost pull" doesn't seem to be a problem for deck supports, probably because the soil isn't particularly loamy.
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
If you're talking about the posts that support the structure, then I will have to respectfully disagree.Around here, we assume a soil bearing capacity of 1500 PSF. If you get a soil test, you can obviously go by those results. A deck footer supporting 50 SF of deck, at 40/10 loading, needs to be designed for 2,500 lbs. So a 16"x16"x8" footer gives use 1.77 SF, which will exceed 2,500 lbs. at the assumed soil bearing capacity.I don't see how a bag of sakrete can be relied upon to give a service life equal to the other components of the deck. Since you're not mixing the concrete, I would bet the strength of the concrete is much below the 4,000 PSI design strength that the standard bags are supposed to yield. Since the height of the footer is only the thickness of the bag, would you not have a bearing area that may only be a foot square? Maye even less?Maybe your area is much different than our (I'm sure it is) and the soil has a bearing capacity of >3k#/SF, but it just doesn't seem reliable to me to do it that way.
Jon Blakemore RappahannockINC.com Fredericksburg, VA
I rely on time tested methods that have worked for at least a generation here, learning what works and what doesn't from having demoed a lot as new money pays to rebuild bigger or different.But since you like numbers, I'd wager that a common strain is to find more solid soil at anywhere from 3-5 feet down, capable of bearing closer to 2000PSF than your 1500at a spread on the bag of 1.77 that can handle 3500#.Spacing posts at 6-8 feet apart( depending on railing layout) you are loading with no more than that.And like I said, time has proven it to work.I would not use it on some mushy silt or loam, or where a roof would be added over this deck later, but for a plain old deck, it works just fine.
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I'm with Piffin. As long as the wood is rated for ground contact, you can bury it and it will likely outlast the above ground portions of the deck. Around here, you have to go to a real lumberyard (or the contractors's desk at a box store) and ask for ".60 treated". Don't just get the stuff of the shelf. If you read the fine print, you will see that it is not rated for ground contact.
The buried poles in pole barns are commonly built by laminating 3 or 4 2x6's. .60 treated 2x6's are spliced onto the below ground portion.
One or the other -- definitely don't embed the posts in concrete.
You can reduce the likelihood of rot on the posts by backfilling them with crushed rock rather than soil. This generally holds better too.
The big advantage of placing the posts in the ground (aside from cost) is that you gain considerable lateral stability -- the posts can't easily move sideways and that helps stabilize the structure they support.