I am looking to put a roof over a octagon shaped patio. I have 4x6 posts at each corner. What size beams would I need to put a pergola styled roof above the patio to span the 12' distance in between the posts?

  • Hello, and welcome to Stack Exchange. A diagram would be helpful (just what is 12' across); it would also help to know your location, and whether you'd need to deal with snow load. – Daniel Griscom May 12 '18 at 15:17

There are two considerations: 1) Structural, and 2) Aesthetics.

1) The pergola is small enough that you could span it with a 2x6. However, it will look weeny.

2) I’d use 4x6 (minimum) beams to match the posts. If you bolt them together they will want to “splay” outward. So, I’d use a gusset plate at the peak to help it keep its shape. Remember, steel connectors are basically “hinges”, so provide plate supports for rigidity or provide cross-ties at the top of your posts. (I like the gussets near the top so it has a “vaulted” appearance.)

Then you could install 2x6 decking on top of the beams. Install each section so the decking is parallel to the bottom edge.

  • Try this for post cap. They come in black too. Be sure to call for the flanges to rotate 90 degrees. (They look dorky when the flanges align with the beam.) fastenersplus.com/… – Lee Sam May 12 '18 at 20:38

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