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Planning to use 4 - 6x6 post, with 2x10 beams sandwitching 6x6 post for 17ftx17ft.

Using 2x6 rafter with 2x2 slats.

Has anyone created 17x17 pergola with 4 posts - any input and suggestion to achieve this is appreciated.

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  • Hello, and welcome to Home Improvement. We'll need more details, and perhaps a diagram. For instance, what do you expect this to hold up? Commented Mar 26, 2019 at 1:22
  • Need details: post to beam bracing, height of posts, spacing of rafters, attachment of beams to posts... Your approximate location is also relevant if you're in wind or seismic zones. Off the top of my head (haven't done the span tables), 17x17 is too big for what you're specifying. Commented Mar 26, 2019 at 2:40

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Assuming the pergola is a “lattice” type roof and not a “solid” roof, (because you mentioned 2x2 slats,) the total load on any one side would be about 1.5 psf for 2x6’s 24” o.c. plus 2.0 psf for 2x2’s 6” o.c. For a total load of about 3.5 psf.

So, the total load on the 2x10’s would be about 3.5 psf x 17’/2 = about 30 plf.

Depending on the species and grade of 2x10’s, one 2x10 spanning 17’ will support about 60 plf. So, two 2x10’s spanning 17’ will support about 120 plf, which indicates your support beams are grossly oversized.

Connection of the 2x10’s to the 6x6’s can be with 3 - 16d, which will support about 100 lbs. each nail.

Of major concern is how the 6x6’s will be supported and stay plumb.

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  • Respect to your knowledge, but if this was your own house, would you actually nail this together with 16d nails? If no, would you suggest lags/ through bolts/ something else? Commented Mar 27, 2019 at 12:42
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There are a variety of options and hardware available for making the mechanic connection between your posts and rafters or beams. I would choose to Use structural screws to fasten the 2x10 material to the posts. Something similar to GRK rugged structural screws or a Simpson type. Through bolts like carriage bolts are also an option as well as hangers.

You should ensure that the 6x6 posts are secured with an appropriate mechanical connection at their base using post base anchors or column base type hardware and that each post is supported at the bottom by a properly sized pier or footing. This will serve as both an Anchor as well as a foundation.

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