Pergola beam span questions


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Old 02-20-08, 01:33 AM
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Pergola beam span questions

I have a 16' w x 12' deep concrete patio. I want to build a pergola over it. I will be using 6x6 posts (cemented in the ground), 2x8 or 2x10 headers or beams at 12' lengths, and rafters 2x6x18' laid on their 2" side with 2x2x12' slats on top. I built a pergola before which was 13' x13'. I did not use more than 4 posts at the corners. Do I need to use any posts in the middle of the 16' span?

thanks
 
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Old 02-21-08, 08:50 AM
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miggidy,

If I'm understanding you correctly, there are a couple of things I would do differently

First, I wouldn't embed the posts in concrete. No way to replace them when they rot. Rather, I would dig and pour the footings and embed CBSQ's in the concrete, then attach the posts to those.

Single or dbl 2X8's or 2X10's for the beams?

2X6's spanning 16 feet? What will support them in the middle?

I would add another pair of posts in the middle of the 16' span with a third beam so the 2X6's don't sag, or break.
 
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Old 02-22-08, 12:30 PM
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Lefty,

I would use 2 2x8's or 2 2x10's to sandwich each post, so a total of 4 for the project.

If I did a middle post on the span, none of my patio furniture would fit, plus the wood on top would not be heavy or load bearing. My last pergola was 15 x 13 with no middle supports and that thing was sturdy. What about using I beams or turning the wood the other direction and span the 2x8 or 2x10 16 feet?

Thanks
Mitch
 
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Old 02-23-08, 04:56 AM
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miggidy,

If I were designing and building it, I would run the beams (triple 2X10's in your case) in the 16' direction, with the posts set 12' apart, so that there is a 2' cantelever of the beam past each post.

Rather than bolt the 2X's to each side of the post, I would cut the post shorter so that the sandwiched 2X's sit ON TOP of the post and are attached to the posts with Simpson BCS2-3/6. (That allows you to attach 3 2X's to a 6X6 post).
 
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Old 05-06-09, 07:53 AM
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Miggity,

May be late on this one, but what direction did you end up going with for your pergola? I am about to construct one with similiar dimensions, only the longest beam span is 14', not 16'. I read what Lefty had to say, but I am unclear as to how running 2x10's on top of posts would help the "sag" factor as much as it would the load factor, which in the case of a pergola is usually not an issue? Could you not run 2x10's sandwhiching the posts, add extra bracing 2' from each post, and add support blocks in between the beams to the same effect? Also, I understand burying posts in concrete can eventually lead to post rot, but I can not imagine the any brace can hold a post in gusty winds as much as the concrete method would in its prime. Beside, would'nt using pressure treated wood, filling gravel at the base of the hole, and the sealing post ends buy you some more time on the lifespan on the posts? A solid 10-15 years would be good for me. Besides, its wood, and I dont expect it to last forever. Open to all suggestions....
 
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Old 10-18-13, 01:00 PM
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Re: Pergola beam span questions

To minimize the odds of wood rot, I would first insert the wooden post (treated or not in tight plastic shell/sheet that rises way above a potential water level. That should seal the wood for a long time. You can also coat the base of the wood in vinyl/latex paint before pouring your concrete.
 
 

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