Setting posts - series of dumb questions

May 3, 2015 11:36 AM

So I'm not much of a DIY person, but I might want to build a pergola along one side of my back yard. Normally I'm a trial-and-error kind of person, but since this would involve concrete-set posts, parts of this have to be right the first time. I still have some questions after googling around.

1. I get how to set the posts and make them plumb and square with each other. What I can't figure out from all the how-tos I've seen is: How do you get the tops level with each other? Careful measurement of the hole depth? Saw the excess off (awkward on a ladder) from the high ones later? Shim the top of the short ones? I'm picturing having all the posts sticking up, then when I go to put the cross beams, the beams aren't level. What then?

2. I guess you do the flooring surface, which would be paving stones, after the posts are in? Can I just have pavers over a gravel bed, or would I have to have concrete under that? (I would prefer to not have concrete)

3. There is a limit to how much area I can cover with a "structure" without having a permit. I want to say it's 200 square feet; I can look that up again. My question about that is, can I cheat and build two 200 sq. ft. structures side by side and have the greenery cover both without a permit? (Which would mean extra posts) Would it be easier to just get the permit?

4. What am I not thinking of?

Thanks. A family member gave us a giant potted clematis and now I have to do something with it.

posted by ctmf to Home & Garden (8 answers total)

1. I'm assuming these posts are going to stick up 8 feet or more and you want to set them so the tops are all level. What I would do is put a pencil mark 3 feet from the top (or whatever will end up being a convenient eye level. Set up post #1 using a couple diagonal 2x4s to keep it solidly vertical. Tie a string around it at the pencil mark, and tie that to post #2 at the pencil mark. Use a level to find out if the string is level, and adjust post #2 by adding or removing fill as needed. Brace #2 with 2x4s When it's nice and level, set post #2. Continue all the way around. The last post should end up level with #1. If it's not, you can figure out where your problem is and adjust accordingly. Pour the concrete when they are all in place, perfectly vertical and all the pencil marks are at the same level.

2. Pavers can go over a gravel bed that's nicely leveled and tamped down. Actually try to have it slope slightly down from the center to all the sides, so you don't get a pool of water in the middle when it rains.

3. Get the permit if your municipality is going to be picky about this.
posted by beagle at 11:49 AM on May 3, 2015

1. I've always set them a bit high and then cut to length. It's not hard with either a sharp handsaw or a circular saw.

2. Yes. The pavers aren't part of the structure, so you can deal with them any way you want -- gravel and/or sand bedding, concrete, etc -- and if it doesn't work out the first time there is no problem for the structure.

3. Permit questions can never be answered in the abstract. (What you are describing wouldn't need a permit at all where I am, for example.) It is usually a really helpful step to just go in and talk to the front desk person at the planning/building department (as compared to calling or emailing, so you can show them your drawing and they can pull up your property on the computer). They can explain how the rules really work (which isn't always the same as what you see on the website) and if they are feeling nice that day they will help with those "change this one thing and then an expensive permit won't be needed" design issues that you are asking about.

4. Don't forget to carefully brace each post and triple check that it is vertical before pouring the concrete.
posted by Dip Flash at 11:51 AM on May 3, 2015

For the height: We didn't get the tops to match. How would you? It's not like the dirt is perfectly flat. We used a saw to cut off the top after we finished building things. My husband used a handsaw, but I don't know if that's the easiest.
posted by ethidda at 11:54 AM on May 3, 2015

Put a temporary stake in the ground at the high end of your fence line, taller than you want it to be. Put another stake in the ground at the far end of your fence line, then run a piece of taut string between them at the height you want all your fence posts to be. Make sure the sting is level, then you can dig your holes beneath it that you intend to set your posts in using the string to plumb the spots for the centers of the holes, & then measure from the bottom of the hole up to the string to give you the length you need for each of the posts. It'll be accurate within a close enough tolerance that it will look fine at a distance, i would think.
posted by Devils Rancher at 11:54 AM on May 3, 2015

Would post spikes be an option?
posted by essexjan at 12:08 PM on May 3, 2015

Regarding my answer above, I pictured this as round or hexagonal structure, hence my reference to the last post matching up to Post #1. But it's the same process for a line of posts, if that's what the config is. However, the cut-it-off option is probably much easier.
posted by beagle at 12:24 PM on May 3, 2015

Use a water level to get the posts all the same height. A single piece of clear tubing a bit longer than the widest span, fill it with ice tea, and bring one end to post A and one end to post B. Mark the height of the water at each. They are level. It is both simple and accurate. It will take five minutes longer to master than using a level, but it will be perfect.
posted by mearls at 6:59 PM on May 3, 2015 [1 favorite]

My personal belief is that wood doesn't belong in the ground, even in concrete, because that will make it wet and wet wood eventually rots as well as being a termite magnet. Preservative schmervative.

If you design your pergola with stirrups under the posts, you can get the stirrup bases level with each other by tacking them to temporary formwork with their legs dangling into the holes, before you pour in the concrete. Then getting the post tops level simply involves making all the posts the same length.

Using stirrups necessarily involves a bolted joint at the bottom of the post, so individual posts won't have much resistance to swaying; some form of diagonal bracing will be needed to keep your pergola from being the wibbly wobbly pergola of death. I used 6mm galvanized wire rope and turnbuckles on ours, which looks nice and works well.

If yours is going to back up to a fence line, you can run an X of bracing cables corner to corner on the fence side and corner to corner on the roof. That will be enough to keep the whole thing rigid without needing bracing on the other three sides, which gives you unrestricted access between the posts. If it butts up to your house and one side of the roof is rigidly attached to a rail along the house wall, you only need the X across the roof.

If the aspect ratio of the roof or the braced side is more than about 2:1, you're better off with XX shaped bracing instead of a single corner-to-corner X.
posted by flabdablet at 11:28 AM on May 4, 2015 [1 favorite]