Deck post technique

[dgbldr]

Around here 2 methods are pretty equally seen:
1. Stick the post in the hole (in the ground), fill the hole with concrete, or
2. Fill the hole with concrete (sonotubes), then anchor the post to top of concrete with hardware.

The posts are then often used as rail posts by wrapping. I'm curious if anyone has enough experience with both methods to say which is less susceptible to post twist/warp. I know there are other pros/cons, but post twist/warp seems to be creeping up to major status lately with the quality of PT wood.

We're talking low decks, 2-3 ft off the ground.

[MarkMc]

A 5' post will have less total twist than the same as a 10', more or less.

[Greg Di]

Around here 2 methods are pretty equally seen:
1. Stick the post in the hole (in the ground), fill the hole with concrete, or
2. Fill the hole with concrete (sonotubes), then anchor the post to top of concrete with hardware.

The posts are then often used as rail posts by wrapping. I'm curious if anyone has enough experience with both methods to say which is less susceptible to post twist/warp. I know there are other pros/cons, but post twist/warp seems to be creeping up to major status lately with the quality of PT wood.

We're talking low decks, 2-3 ft off the ground.

How you anchor it makes no difference. Either way, it's a crapshoot. The best defense is a good, clear contract with language in it that explains the unpredictability of wood and how you are not responsible for what it does.

Wood's unpredictability is the main reason I am no longer framing with PT wood and have switched to steel.

[dgbldr]

Wood's unpredictability is the main reason I am no longer framing with PT wood and have switched to steel.

Are we talking that Trex type of steel? What do you use for posts?

[Top Notch]

They say if you treat the ends of the field cuts before the end grains see water or dry out you will limit the twisting.

Some people like to sink a post in a hole on 12" pad below grade then back fill it with stone which provides better vertical stability. Then there are people like me that dont like burying a post because I think it cant be good even though its treated so I add tons of un necessary concrete to a hole then anchor it on top. ;)

I do my railing posts at the framing stage so I coat the top with copper then run a 2x4 across them to temporarily keep them in line and hold them from twisting out of whack before the railings and sleeves do the job.

[tjbnwi]

I like to use the Redi-Footings. I don't bury the wood posts.

Tom

[jimAKAblue]

On a deck that is 2 or 3 feet off the ground, I always liked to bury the post. You have to dig 42" anyways and I'd just drop a few inches of gravel and then a 10' post. I'd use the exterior rim joist to lock the post at the mid point and when everything was done, it was all rock solid. I never experienced any trouble with twisting but I haven't seen what your stock looks like for a few years.

If the stock is that bad, you probably should think about changing the style of the posts by wrapping each post with a 1x veneer and let the post float in space in the hollow created by the veneer.

[dgbldr]

I like to use the Redi-Footings. I don't bury the wood posts.

Tom

Yes but what about the rail posts?

I'm thinking along Jim's lines. If you bury the post in concrete, that holds one end fixed real well. If you then bolt it to the deck structure (girder or rim, depending on design), you've restrained it positively at 2 points. Would that not resist most of the twisting stresses in the post?

[tjbnwi]

The Redi-Footing is just an extension of post. The post is captured in the yoke then bolted.

If you are bolting the posts to the rim, do wait until the frame work is done and then fill the holes with concrete? Trying to get the post that perfect has always been an issue.

I hold my beams back from the rim. My rail posts are captured In pockets for strength. I have had a few posts twist, not many in the schema of things.

Tom

[jimAKAblue]

If you are bolting the posts to the rim, do wait until the frame work is done and then fill the holes with concrete? Trying to get the post that perfect has always been an issue.

Tom

I never waited till the framework was done. I set my corners, then run my rims. I temp braced the rims (to keep them straight) and used them as the baseline. I then dropped the posts in the hole, fastened to the rim, plumb and fill.

My system involves working the posts and rim and holes simultaneously as opposed to setting all the posts, then installing the rim.

I do agree with temp bracing the tops if the rail won't be installed quickly. I was always able to get the rail started within a very short time frame, so that extra step wasn't required.

[Greg Di]

Are we talking that Trex type of steel? What do you use for posts?

Not the Trex system.

Light gauge steel C-Joists.

[TSJHD1]

The wood's gonna do what it's gonna do, then it will stop. At least that's my belief. So several years ago I started getting treated lumber on-site several weeks before it was to be used. Mainly, stair stringer material at first, but then I expanded to include any items that would give me problems if after they dried out, their size would change too much (or twist, etc.)

So I'll stack up the lumber and separate the individual pieces with rips of whatever is lying around. 3/4 ply gets ripped 3/4" wide, then cut into short pieces. 2x4's can get run through a table saw to make 3/4 x 3/4 square rips. Then I place 3 pieces between each board, one in the middle, and one a few feet from each end. Cover the lumber and let it sit for a while.

Tom

[Greg Di]

The wood's gonna do what it's gonna do, then it will stop. At least that's my belief. So several years ago I started getting treated lumber on-site several weeks before it was to be used. Mainly, stair stringer material at first, but then I expanded to include any items that would give me problems if after they dried out, their size would change too much (or twist, etc.)

So I'll stack up the lumber and separate the individual pieces with rips of whatever is lying around. 3/4 ply gets ripped 3/4" wide, then cut into short pieces. 2x4's can get run through a table saw to make 3/4 x 3/4 square rips. Then I place 3 pieces between each board, one in the middle, and one a few feet from each end. Cover the lumber and let it sit for a while.

Tom

Wow...that's a lot of effort. I could not imagine "babysitting" material like that for a deck...any deck...heck, any project.

[Lavrans]

Yes but what about the rail posts?

I'm thinking along Jim's lines. If you bury the post in concrete, that holds one end fixed real well. If you then bolt it to the deck structure (girder or rim, depending on design), you've restrained it positively at 2 points. Would that not resist most of the twisting stresses in the post?

Not really, especially with PT- depending on the PT, I suppose. It's rare that a post can be restrained at the top well enough to prevent twisting, and even if it is, there's a good chance the post will check or split all the way through.

I do something like Tom mentioned; get it early and let it sit. I also like to cut to rough size first. For a small deck that's difficult. If it's a larger project, then there's space and time, and it's not really that bad.

As much as anything this is one of those places where design comes into play. I really try to do over-the-post railings, especially with exposed PT posts. That way the post can twist and it won't be as noticeable as a post that has the railing butting to it, that now has big wedges where the post has twisted. I find that they don't move all that much, especially if you select them carefully, but a 1/2" twist will look bad if there is some place to see it.

[Greg Di]

Disclaimer, disclaimer, disclaimer...

If God forbid, someone still wants to install a PT deck, you absolutely need to tell them, in writing, what is going to happen and that it's completely beyond your control.

You can go through all these motions and still get insane movement despite your best efforts. If someone is only paying for the drivel of a PT deck, you shouldn't have to put any time into culling, precutting and staging wood on site. Use better material, save all the labor and sell it that way. #2 WRC is not that much more and is a million times better (but still not great but it gives you a fighting chance).