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Discussion Starter · #1 ·
I am designing a pergola which I plan on using 20' 2 x 10 pt lumber. The rafters will span 18' an cantilever 2'. There will be 4 6 x 6 spaced evenly across a 20' span. Will the rafters sag with a 18' span?
 

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I don't understand. Do you mean the 4 6x6's will be under the 2x10's? If so, the 2x10's won't be spanning 19', they will only be spanning the distance between the 6x6's.

How far do the 6x6's span and what will be under them?
 

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Discussion Starter · #5 ·
The material used is pressure treated 2 x 10 for the rafters and girder. The 6 x 6 post will be spaced approximately 5 ft apart. There will a ledger board attached to the house and I will use concealed joist hangers. The girder will be 18' from the house. Will 2 x 10 not sag over 18'?
 

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Discussion Starter · #7 ·
Yes, the flange is essentially in the inside, typically used for the end joist if a deck.
 

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I question the use of treated lumber for a pergola to begin with.

If you use 16" centers & install a couple of rows of bridging blocks there prolly won't be much if any sag tho. Why not go with 2x12's instead of 2x10's?
 

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I would say that yes you will have a sag. Whether it will be enough that it will be noticable, I can't say.

I'm sure that our PT is different, but I would never even considerate it for a pergola. It could get ugly fast.
Yeah but pt is still pt, and all of it is a bastard when not constricted. The only time I would use pt for a pergola is if its getting covered in vines and even then it gets painted. Maybe its me but I would say yes, 18 ft a 2x10 will sag.

Can you run a box beam down the center with some cripples in it?
 
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