Pergola Post Options

bindersbee(6a UT)August 3, 2006

Man, I had this all typed out last night and I don't know what happened to my post- operator error no doubt!

Anyway, I am building a 14' x 14' pergola. Dh will help but it isn't a big priority to him (until I actually start on it- then he'll come help because he won't want me to do it wrong, LOL! He's such a perfectionist, but I digress). I have the plan worked out for the upper structure and know what I'm doing there but I wanted to get some opinions on the post possibilities. Oh- the upper structure will be made with Southern Yellow Pine. I got an awesome deal on it as it was leftover from a local project (outdoor playground). It's not like regular pine, much denser and rated for outdoor use.

So, for the size of the pergola, I think 6 x 6 posts would be best for strength as well as visual weight. The big dilemma is whether to cement them in (30" is depth of frost line here) or use shorter posts on stirrups, U-brackets or whatever the official name is. I'd like to cement them in because then I could hang a swing or two off the ends with the double sandwich 2x10's. I couldn't do that if we did the U-brackets. However, in-ground would shorten the lifespan of the structure. U-brackets would be okay but I just worry if they are really strong enough?

WWYD? Are there other options? Metal posts covered with boxed columns? Fiberglass columns (probably too expensive)? Would metal corrode over time if in ground too? Where would I even buy such posts? Ideas/ recommendations please! TIA!

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jake(z4b-5 NE)

Buried will give you very stable columns for a swing no doubt. I on the other hand built a 14 x 14 deck w/ swing cantilevered 18" outside the deck frame. I placed the column(s) on 12" dia. footing(s) (buried 42" Â frost depth here) and sticking up 6" above grade.

This 6" above grade keeps the post out of contact w/ dirt, as we know dirt deteriorates the wood product.

Rather then using stirrups I put an 18" x 3", #4 rebar in the footing sticking 6" in the air. Buried 12" w/ 3" bend to keep the rebar in place. Drilled a 6" x 1/2" hole in the post / column, slid the post over the rebar.

The whole deck had a roof over it thus making the "floating" columns more stable.

Diagonal or cross bracing (sometimes called "knee" brace) should be added to your pergola regardless of the post / column anchoring method you choose.

As for stirrups there is a national company that makes several different stirrups for various uses. You should be able to locate these stirrups at any home cheapo or other like stores.

These stirrups should be galvanized for outdoor use. Same with any nails, bolts, nuts and washers, they should be galvanized, zinc coated, brass or stainless steel.

If you bury the posts / columns I would go at least 36" - 42" deep for better stability.


    Bookmark   August 3, 2006 at 4:41PM
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bindersbee(6a UT)

Thanks Jake! I really should know how to do all this- I have a BLA (Landscape Architecture) degree- but I ended up working in a parallel field after college (City Planning) so my landscape construction skills are not at all where the should be. What you don't use, you lose. So, as embarassing as it is to have to ask, well, I gotta ask! Thank goodness there are experts here to help- I know just enough to be dangerous!

    Bookmark   August 3, 2006 at 5:39PM
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jake(z4b-5 NE)

Happy to offer whatever it is that I have to assist others like you and myself.

I have drgrees in Arch. Drafting & Design also a drgree in Horticulture, major in Landscape Design - minor in Nursery / Garden Center Management and what do I do ???

Get a job w/ the City doing CADD management and drafting supervisor for 33 years plus having my own residential and landscape design business for the past 26 years.

Some day i am going to decide what I want to do for a living, after I grow up and get older.


    Bookmark   August 4, 2006 at 11:57AM
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bindersbee(6a UT)

Ah, so you understand. Yes, those cushy City benefits and reliable salary were too much of a temptation for me to pass up straight out of school. I grew up with a wonderful Father who was a self-employed cabinet maker/ master craftsman. He's taught me a lot but one of the things I learned was that I hated the feast/ famine part of being self-employed!

If I get in over my head actually building this thing, I'll be calling my Daddy! No, I understand how it all goes together but I'm sure it will take more than me to heft some of this stuff into place!

I keep thinking I'll start doing some design work on the side (I've also worked for nurseries here and there and have kept up on my plantsmanship) but I need a little more experience first.


    Bookmark   August 4, 2006 at 2:07PM
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It should be possible to build a stable 14' x 14' pergola without relying on the footing although local codes may demand it. If you have a stable four square structure all you need is something to keep the posts off the ground. If cost is an issue you could also put the posts directly into soil or gravel without concrete and when the bottom rots out put concrete and stirrups in at that time.

    Bookmark   August 6, 2006 at 3:03PM
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I completed a 12' x 12' Western Red Cedar pergola last October. I used 6 x 6 posts and two 4 x 10 beams as my lintels (attached with simpson strong-tie connectors...had to be custom fabricated.

In any event I dug down below my frost line and put in concrete footers (rebar reinforced). I then put in a nice cobble paver patio above it. I attached post connectors to the footers (after removing the pavers) by drilling into them and using hydrolic cement to secure the bolts for the post holders. Make sure you pre drill everything so you do not split your wood!

I coated the bottom and lower portion of my 6 x 6 posts with roofing tar just to make sure there were no issues. The tar that was left above grade was covered by my boxing out the bottom of the posts anyhow. Almost one year later and no problems. Used all stainless connectors (did not want an issue with staining my beautiful cedar).

As stated above make sure you cross brace the structure. Should be at least 3' down the post and 3' across the lintel for adequate bracing. If I knew how to include a picture in the post I would.

Good Luck!


    Bookmark   August 7, 2006 at 11:58AM
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joefromsd(San Diego)

Here's the way I usually set pergola and patio cover posts when I don't want to use knee braces.

Slope the top of the footing a bit so it drains well, then wrap it with copper, which will kill all the rot and mold at ground level, and looks pretty nice too!

Now let's see if I can get this to post!

    Bookmark   August 7, 2006 at 8:25PM
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bindersbee(6a UT)

I love this website. So many knowledgeable people here! I LOVE the copper banding. I have a not-so-beautiful view of Kennecott Copper Mine from my back yard (largest open pit mine in the world) but the upshot is that copper is an indiginous material here and just 'looks right' in my area. I will definitely do that!

That's a very nicely engineered way to do this. Thank you for the wonderful construction detail drawing and photo. That helps a lot!

    Bookmark   August 8, 2006 at 2:46AM
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Copper is a great idea...looks nice, although I personally prefer boxing out the column bases...I suppose one could do both. In any event the only other suggestion I would make would be to place the post into the cement and let them set before you cut them to length (height).

This way you can use a line level (or even better 2x4) to be tacked across the posts to give you a base to cut the post so that all of your posts are exactly the same height.

I am afraid with my meager skills I would never be able to set all of my posts so that exactly the same amount was left above ground!

If anyone can help me figure out how to post pics in here, I would like to include 2 (somewhat crappy) pics taken with my camera phone!

    Bookmark   August 8, 2006 at 2:22PM
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joefromsd(San Diego)

Scale, you need to use a Builders Level or Transit to shoot the bottom of the hole after it's partially filled with concrete. Make sure the concrete is level at the bottom, I usually use a piece of 2x4 to pat it down flat. After it sets up (next day usually) then you can shoot it and cut the posts very accuratly.

    Bookmark   August 8, 2006 at 8:56PM
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bindersbee(6a UT)

Actually, I'm pretty sure I will wait to trim the height until after it's all set. It will be enough for me to make sure they are all plum and properly aligned. I'll worry about the length after. Once I have the 2 x 10's sandwiched into place and the 2 x 6's that are going the opposite direction, I'll cut the remaining part of the tops off with a circular saw.

    Bookmark   August 9, 2006 at 12:47AM
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karinl(BC Z8)

scalesmd, to post a picture here you need to open an account on a webhosting site like Photobucket - it's free. Upload photos from your computer to the photobucket account. In Photobucket, each photo will have a TAG line. Copy that line to the text of your message here. When you hit "preview message" your photos should appear.

Hey bindersbee, this is a great question, and is relevant to fenceposts as well. We've been pondering how to do those so that the task of replacing them doesn't loom quite so quickly. Or, how to set them so that they can be easily replaced. So I'm very grateful for the responses too.

There is also that new wood product made from recycled tetrapaks or something - Trex in the US I think? I think they focus on decking though, maybe don't make 6x6 posts.

    Bookmark   August 10, 2006 at 2:12AM
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bindersbee(6a UT)

I am intimately aquainted with Trex- great product. There are 6 x 6 structural plastic posts which can be purchased from Bedford Industries. I actually have access to 3 6x6 x16' posts for cheap- just not 4! They are incredibly heavy but are engineered to be load bearing. If it weren't so difficult to obtain another post- I'd totally go that route. I'd never have to worry about rotting but, a 3 legged pergola isn't the look I'm going for!

    Bookmark   August 10, 2006 at 6:52PM
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madtripper(5/6 Guelph)

I have just built a pergola using the U-brackets. I am not very satisfied with the results. Teh U-brackets have some give to them and so I can easily wobble the structure. Everything is solid and you can see the movement right at the U-bracket.

I'll have to add some cross bracing which I have not yet done.

    Bookmark   August 11, 2006 at 8:38PM
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jake(z4b-5 NE)

Even when one builds a "pergola" or arch of some sort and when the posts are buried, it is always adviseable to install "knee" bracing at the corners and possibly even on the interior posts.

These knee braces sturdy the construction both laterally and help in vertical support also.

Defintely at the corners.

Weebles - wobble. Pergolas shouldn't.


    Bookmark   August 14, 2006 at 4:26PM
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Please get me started! I am planning to have a 14' deep concrete patio poured next month. I have decided to install a freestanding 10' x 12' pergola also. How is the best way to do this? Do I need to install the post or bracket into wet concrete or wait until all the concrete work is done and then begin the pergola?

    Bookmark   February 12, 2011 at 10:44AM
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