I’m building a cedar pergola with 6×6 post, 2×12 beams sanwiched on each side the the posts, and 2×8 joists across the beams.
The overall size is 25′ x 14′. The post on the long 25′ side are 22′ apart with a post in the middle.
The longest 2×12 beams I can get are 20′, so I will have to use 2 2×12’s to reach across the 3 post but I dont think its a good idea to butt joint the 2×12’s together on the sides of the middle 6×6 post. So I thought of this concept shown in the sketch to have seperate levels so I could get a good solid attachment for each 2×12 beam to the posts with bolts.
Does this sound like a good worthwhile idea or is butting 2×12’s on the side of a single 6×6 post acceptable?
Replies
I think the above design creates more "visual interest" than butted beams on the same level.
Strength wise, the butted 2x's are probably acceptable. But what you've drawn is much more visually appealing.
I think you can further refine the plan by extending the overlapped 2x beams a tad more. And, perhaps, raise the upper one some to give a bit of separation. A third level isn't out of the question although that will add complexity, effort, and expense.
More aesthetics: The bolts you show holding the 2x's to the posts would be better recessed and plugged. Use galvanized bolts, not zinc plated. Keep any bare steel away or you will get black streaking on the cedar.
It will smell great right after you're finished!
Good luck recessing and pluging a bolt in 1 1/2" of lumber and still have anything left for strength.
New Design - Scarf joint on beams
Looking into glulam beams.
I've also been reading up on scarf joints.
Is this the correct scarf joint pattern to use on 2x12's
That scarf joint would be great on a big timber, but could potentially cause a 2x softwood plank to split or be more rot prone. I would stick with a basic butt joint. Also, you should consider insetting the beam into the post so the beam is in compression instead of in tension. Hanging the beam on a few carriage bolts is weaker.
I like the other design better.
If you're going to scarf then do it across the width of the board, not across it's thickness. A 12:1 ratio would be about right, but that is a vague memory so you ought to look into it some more. The scarf can be easily done using a hand plane. A power plane will speed up the process. Use epoxy thickened with wood flour to do the gluing. First paint on unthickened epoxy to wet out the wood, then the thicke stuff. Clamp, but not too tight.
I still like the multi level design better.
The advice to cut seats into the posts is good.