I’m wondering what peoples thoughts are as far as how to do deck support columns. Years ago when I built decks part time it was standard procedure to put some concrete into the hole, drop the post down into the hole and fill the rest with concrete. Now there seems to be alot of different types of mounting brackets that are set into the concrete at pour and then the post is attached to the bracket.
The deck I’m going to build will be raised some 8 feet off the ground due to grade of property and so I’m leaning towards setting posts into the concrete to increase the strength of the structure against lateral movement.
So what are the pros and cons of each?
Thanks!
TWOTTER
Replies
I don't know if lateral movement CAN be prevented by the manner in which you choose to anchor your posts to the footings. Rather I think that's an issue that needs to be addressed in the deck design and how it's braced.
Here's the footing detail I've used successfully for 2 decades in applications up to 16' high. I usually address the lateral movement concerns by running the decking diagonally. It offers good cross-bracing and is fairly easy on the eyes. Add 15% to your decking order.
View Image
That's just a 12" long #4 rebar pin that I've layed out to hit the center of the 6x6. Backfill 2/3 with crusher run, rest with dirt. Never move.
Interesting.
Are you doing this in an area subject to freezing. I guess I'm wondering what happens when you get some freeze thaw action around the bottom of the 6x6.
I'm in Eastern Ontario Canada so its a consideration.
I agree about the bracing to control lateral strength. I guess I was thinking of lower decks where I think posts in concrete are stronger than bolting the posts to brackets on top of footings and you don't need to brace.
Cheers,
TWOTTER
I'm in southwest VA where frost heave isn't a major concern, but when I worked in northern NJ we didit the same way--just deeper.
The main thing, as was echoed throughout the thread, is not to encase your posts in concrete.
If you happen to like, or maybe required by code to use, the fancy anchoring hdwr., that's probably money not wasted.
Don't pour concrete around your posts. It shortens the post life as essentially, the post bottoms will always be wet. I understand though that imbedding the posts in concrete adds a fair amount of lateral stability to a deck, although like David Hawks says there are other ways to brace a deck, including knee bracing and cross bracing between posts and deck floor structure. Diagonal decking is OK, if it fits the style of the home. Take a 150 yr old home, or one styled like that and run the decking boards diagonally? - barf! It does look good though on a modern or transitional style home. You still need the bracing on the posts though. Some planning is necessary to get the braces to line up with the posts and the deck beam/girder.
Back to the deck posts... There are a number of types of base/brackets available to connect the post to the footer concrete. The idea is to take the post out of contact with the concrete. This is what I like to do: Dig your holes. Fasten your brackets to the bottoms of the posts. Here is one example of a post bracket. Erect your posts and enough of the structure to hold the posts in place and get everything squared up. Your posts are basically just suspended above the holes. Temp stiff knees can be used to hold up the deck beam(s) etc. Temp braces of 2x4 scraps can be nailed horizontally across the post at grade level to support the posts above the hole. Now that you have everything squared up, plumbed and leveled, place your mixed concrete around the post filling the footer hole so that the concrete comes just to the correct level on the post bracket. This method lets you get your post brackets/anchor bolts/whatever placed in exactly the right spot. Now let it set up for a day or 2 and then resume working. I have actually even built the entire deck using this method, pouring the concrete last. Makes for an easy inspection cycle too, but you gotta be very sure your post holes will be acceptable to the inspector. At the very least, you can continue working while waiting for the inspector to show up to check your footer holes - if that is the way it is done where you live. Also, you don't want to let much of any rain water get in your footer holes as it is rather hard to clean them out with a post in the way.
BTW: our building code requires 6x6s for decks > 8' above grade. You might want to check your code.
Good luck with it!
Matt
Edited 1/26/2007 12:30 am ET by Matt
Thanks Matt. Good points made and i really appreciate the links. Good info there too.
Cheers,
TWOTTER
You're right, diag. run decking isn't gonna work on every style home. Guess I've been in the land of the 3/2 ranch too long, where a simple detail like that is a sure-fire recipie for referrals and repeat business.
Thanks for the memory jog.
Thanks all, good ideas for sure.
I think I'm going to go with the brackets on top of a footing. I like the idea primarily because it gets the column completly out of the ground and it seems like the best option with regards to rotting the columns out over the years.
Cheers,
TWOTTER
I usually rent a post hole digger and dig a 16 inch diameter hole down past my frost line; which is 3ft, so I dig down to about 4 foot. I place a couple of inches of gravel in the hole and then pour a concrete punch pad about 6 inches thick.
A drift pin is a very good idea, but I usually don't use one and instead install my posts down onto the punch pad , I brace my posts and then proceed to build my deck in place. One of the last things I do is backfill the posts...reason being so I can manipulate the posts if I need to tweak the deck so it is square before running the decking. Once my deck frame is up, and squared away, I then backfill the posts with the dirt that originally was excavated, and I add a bag of dry Sacrete in with the dirt. I tamp the fill in place and then water it down just a bit . The dry Sacrete helps to firm up the existing fill, yet it is not a concrete consisitency and so does not pose the same problems that in ground concreted posts usually face.
I always use 6x6s for posts 8 foot or higher. I would much rather have my posts buried in the ground than simply bolted on top of a pier. I too believe buried posts gives a deck more stability than those above ground. I stay away from concreting posts in the ground...even treated posts can still rot out over time using this method.
Davo
I understand that in some places with certain soils in the south or midwest, you can get away with sticking the post in the concrete, but in most places where I have seen that, it causes early failure.
The post allows water into the cavity in the crete, which then freezes and splits the crete apart. leaving nothing.
Also, the water being held keeps the post damp and accelerates rot and water damage, even in PT posts. Simpsons new post mount brackets allow for an inch or so of adjustment for more accurate placement than what I imagine you can get by setting posts in crete.
An earlier method before these was to leave a ceenter rebar standing 2-3 inches out of the crete and then drill a corresponding hole in the bottom of the post to keep it located on the pier.
When building tall like you mention, we use small diagonal kickers from deck beam to post to keep it all stabilized. Most of our decks get a lattice surround to hide the underbelly too.
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