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-   -   Pergola Beam Question (http://www.diychatroom.com/f19/pergola-beam-question-135425/)

jallred1 02-28-2012 10:33 PM

Pergola Beam Question
 
Hello,
I've read a few topics on this, but thought I'd confirm my suspicion that this might not work. I'm planning on building a pergola over my deck and want to place the support posts on the perimeter of the deck, having the posts double in some spots as railing posts and pergola posts (if that makes sense). The expanses between the posts are 12' on one side and 16' on the other. I was planning on building the pergola with douglas fir using:
4 6x6 posts, anchored on top of a poured footing, coming up through the deck and/or railing
4 2x8 support beams sandwiching the posts running in the 16' direction with lag bolts holding them (20' beams total...two feet overhang on each side)
12 2x6 top beams running in the 12' direction (16' beams total...two feet overhang on each side)

My biggest worry is that I will see sagging in the 16' 2x8 support beams in a couple years. Unfortunately, I can't add in a middle post to break up the expanse, as I have a built in bar under the expanse. I'm wondering if I will be okay or if I should completely redesign the pergola. Any help would be greatly appreciated. Thank you.

robertcdf 02-28-2012 11:06 PM

I would personally upsize the beam and the joists 1 size (to 2x10). The beam would be better off if doubled instead of split onto each side of the posts, doubled material is always stronger than 2 singles.

getzjd 04-03-2012 09:31 PM

I built a 20x20 pergola and went with 2x12's for the beams and 2x10 for the joists. For the few dollars difference, why not?

http://farm3.static.flickr.com/2511/...33b02f20_b.jpg

cortell 04-04-2012 08:40 AM

Someone in our neighborhood has a front-yard pergola built with 2x6 beams. It has a HUGE sag in it and looks awful. I'd definitely go with 2x10 or 2x12. As getzjd said, it's not going to make a huge difference in final cost, and it's going to look much better.

Also, it's a matter of fact that going with a deeper piece of lumber is more effective (with regards to stiffening) than doubling up. I.e., one 2x10 will be stiffer than two 2x8s.

getzjd 04-04-2012 09:04 AM

Quote:

Originally Posted by cortell (Post 891499)
Someone in our neighborhood has a front-yard pergola built with 2x6 beams. It has a HUGE sag in it and looks awful. I'd definitely go with 2x10 or 2x12. As getzjd said, it's not going to make a huge difference in final cost, and it's going to look much better.

Also, it's a matter of fact that going with a deeper piece of lumber is more effective (with regards to stiffening) than doubling up. I.e., one 2x10 will be stiffer than two 2x8s.


Funny you say that about the 2x6 beams. On my way home from work every day, I pass a neighborhood pool complex with a sagging pergola. Almost looks like it is smiling at me.

juryduty 04-04-2012 10:06 PM

Personally I prefer the single larger beam to the sandwiching 2x. Everybody seems to like the sandwiching with lag bolts. I guess it is cheaper. If it is allowed by the inspector, why not go with something like a 6x8 beam and a Simpson CCQ post cap.

Calalex 05-29-2012 06:57 PM

2 Attachment(s)
Hey getzjd, how did you fastened your beams and knee braces. i am currently working on a very similar project and I am getting a bit of movement if you shake the post vigorously. How low are your knee braces going? Any feedback is greatly appreciated. nice job by the way i hope to have mine look like yours. you can look up my thread under "pergola movement"

i have attached pics

getzjd 07-08-2012 05:37 PM

Sorry for the delay, but I simply drilled through and bolted my knee braces in. I do have extra bracing though as I was able to bolt to the beams on my deck as well.

I will check out your thread, see what the status is and offer up some ideas.


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