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I'm trying get some advice on whether this design is even possible and if so if my post size and joists are correct (ie safe/structurally sound). I have seen many cantilevered pergolas so I think this T shape design is possible, but I am concerned that my width, 17 ft, is too wide for a design that only has one post to hold up each joist.

I am trying to create a T shaped pergola which a canvas material will be stretched across.

The dimension of design shown are for both posts to be 6"x6" cedar 12ft and 13 ft tall. 6.5' apart.

I am planning to secure each post with a footer 4 ft deep and 18" diameter. Is this deep enough?

The joists are the part I am most concerned about as they are 17ft wide (2"x6" cedar) with the post in the middle, so the beam will span 8.25ft to each side. Is this possible to do with not other posts?

If it matters, the property is located in Dallas, TX.

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  • Sure it’s possible but it will take a good (large) footing the depth sounds right but I would guess at 24-36 wide as a wag and 4x6 or 4x8 posts. If you have wind issues I can see even that being ripped apart.
    – Ed Beal
    Commented May 6, 2021 at 23:07
  • Lol we definitely have wind issues in Dallas, but I wouldn't mind going with larger footings and 6x6 or 8x8 posts. Additionally, the footing will be under a 6" concrete patio.
    – Luke Stone
    Commented May 6, 2021 at 23:19
  • I haven't done the math but I am skeptical that would be sufficiently rigid. That's not a whole lot larger than a fence post's footing, and this will need considerably more strength than a fence post. Commented May 7, 2021 at 6:29
  • You would definitely want some diagonal bracing between the posts and rafters, and between the posts themselves. If you cover this with canvas, you've created huge sail to catch all that lovely wind you get there in Dallas. I'd think that even with a light breeze you're going to be putting some fairly massive stress on those joints.
    – FreeMan
    Commented May 7, 2021 at 13:58
  • My gut is that this is a weak design, especially with the idea of a sail on top. If I had to do this for a client, I'd get 1/2" steel T-shaped braces (~5' per leg) and through bolt them. I'd also have the client sign away their right to sue. Have you considered this in welded steel? 4x6 box section seems reasonable. (And put vents in the canvas top so it doesn't turn into a sail.) Commented May 8, 2021 at 18:43

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