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Joinery for octagonal screened porch #35903 03/07/21 12:55 AM
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Oldfart Offline OP
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I dreamed up a frame for the porch sketched in by architect with no detail save roof pitch, wall length, wall height, and roof overhang.

See the pics. Roof pitch is 9:12. I have it with 5x10 beams connected to 6x6 posts, 4x8 hips and 4x6 rafters, one rafter per bay. A shaped centerpost from 10x10 stock heads all the ridge members, and the rafters pinch in between.

There is plenty of structure here for the snow load, more than enough, really. I sized the members (yes, [/i]5[i]x10s, all to have it achieve a light look, not chunky at all.

The question here is what about the connection at each corner? Hip to post, beam to post. I have the hip mortised, the top of post tenoned, and skewed mortises in the posts are for the offset tenons at beam ends.

Each of the 8 sides is about 7'1" long. I show a "bent" which is the section through a pair of opposing hips. The 3.5x6 ties are only on half of the "bents."

Does the joint seem reasonable?

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Re: Joinery for octagonal screened porch [Re: Oldfart] #35904 03/09/21 03:21 AM
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timberwrestler Offline
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You could shape the posts to have 5 sides to simplify post to beam joinery.

The ring of plates is in tension from the rafters pushing down and out, so you should consider that.

Lowering the ties to run plate to plate could help with that.

Lastly, because there are so many rafters converging to one point, you could put short (purlin) headers between the hips about 1/3 from the top, and have the common rafters butt to that. Otherwise, no matter how accurate the cuts, something ends up wonky at the peak. The headers give you a little bit of flexibility.


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