# Pergola cantilever



## oh'mike (Sep 18, 2009)

Typically, if the roof structure is running across two headers---the cantilever can be 25 to 30 percent longer than the supported span---

Do you have a sketch of your proposed structure? Or a picture of someone else s pergola that is similar to what your would like?


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## concrete_joe (Oct 6, 2014)

IBC has some max deflections allowed for cantilever. the materials used, the loads, and length of cantilever will tell you how much cantilever you can do. i have a large patio cover (16x48) with only two support posts off the house, i cantilever a glu-lam ~12.5 feet on each side of the post, makes the roof look like its floating. people think its crazy seeing a cantilever that long, but i am still under max deflection that IBC allows, etc.

once you know the data the modulus for the material in deflection will be key.

look at post #9 here (http://www.diychatroom.com/f49/spa-208358/index4/#post1422494), i am standing under a 12.5 foot cantilever.


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## olson2334 (Mar 12, 2015)

This is what my wife liked and I can't say that I mind it either. The main idea of this would be to cover the walk way on the side of the patio. In addition, at the patios widest point on the patio allow for us to extend it so that the table can be under the cantilever perhaps. 

the below is only that I was thinking one could have the post, and create that triangular support structure(does that make sense. not sure how to describe it but the picture shows it) tied to the post to get the cantilever out a bit further but not sure how far i can go. 

Here was one consideration. (it wont allow me to post a link so know that you have to have www . in front of it. 

progressivelawnscaping.com/?q=images/portfolio/pergolas_screens_and_decks/cantilever_pergola

@concrete_joe wow 12.5 that would be awesome. We had always simply considered using cedar for this project. I didn't know that you could use something like glulam outdoors.


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## concrete_joe (Oct 6, 2014)

the pic shown by your link has lots of support in there, i bet there's very little bending going on. i myself dont like those arc'd support pieces. a design like that will also have some pivot point forces to work out so that the long side of the overhang doesnt rip the thing off of the pivot point. you could removed those arc'd support pieces in favor of a brace (cable or something) on the short side.

what i have is made for exterior use, Rosboro X-Beam glu-lam (3.625" x 12").

there are many materials you can use, just depends on how you want the architecture to be (all wood, all steel, combo, painted, etc etc)


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## olson2334 (Mar 12, 2015)

Thanks for the reply. I am in agreement that I don't care for much of how this looks accept that how it functions in that it is similar to what my wife in i were thinking ours might be built. It is a single post sort of setup that cantilevers out a good distance. I think how we build it would be different to some degree. At least that is what I have in my head.  

I am not sure i understand how you are suggesting removing that curved piece in place of a cable. Were you thinking to tie a cable into the short side and then into the post? If so, wouldn't doing that exaggerate the effect of a wind sort of event if the wind were to get under the cantilever?


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## rwa (May 10, 2009)

Olson and Concrete .... I think one or both of you are talking about span, not cantilever ... listen to oh'mike if you are indeed talking cantilever


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## SPS-1 (Oct 21, 2008)

To answer your first question --- you can cantilever as far as you want, but then design the support accordingly. You are not going to find the answer in the back of a book or on a chart. I expect you will need an engineer to design it if you expect to obtain a permit for it. If you look closely at the link you posted, the post is built up out of 2X pieces. I would not be surprised if there is a steel post behind there embedded deep in concrete. The curved piece in the photo is not just lessening the amount of cantilever, it is a brace. By putting in the brace, they have triangulated the post and beam and made it rigid. Without the brace, the beam at the top hinges at the top of the post. 

4x4 posts, not a chance. 

So really, the answer is anything is possible, but you will need professional help. And of course, the more cantilever you want, the more its going to end up costing.


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## concrete_joe (Oct 6, 2014)

you dont need an engineer to get a permit. i did all my own design and calculations for my patio cover. footings, A500 steel columns, live/dead loads, etc etc.

next, span ?? i am not talking about span, i am talking about cantilever. the pic i showed is a 22ft span between posts, only two posts, and each end is a 12.5ft cantilever past the post. the other side of the roof is on ledger against the house thus approx 1/4 of the load is being carried on each column, and just 1/8 on the cantilever. this is a tad different than the pergola but i was just showing that you can do crazy things with cantilever.

using a 4x4 as post(s)? possible yes, but depending on the cantilever torq (notice i didnt say length or weight because torq is derived from those #'s) the design must handle that torq properly. you can use whatever materials support the design, etc.


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