View Full Version : Strengthening the posts of a pergola.

06-22-2004, 07:37 AM
I have built a 11 x 13 pergola above my deck. I used 4x4 Cedar posts that were notched and carriage bolted into the frame of the deck. The pergola consists of 2 x 8 bolted to the sides of the posts (strongback). The supporting beam of the pergola is about 7' 10" off the deck surface. While the purgola is sound and rigid, the posts have some sway to them (when you try to shake them). I'm not afraid of the thing falling over, but want to reduce the sway of the posts. I've tried diagonal bracing, and it really works to reduce the problem, but it's ugly and i would like to avoid it if possible. One idea i had was to fasten additional 4x4s to the exising posts to create a 4 x 8 posts, will this create a nice rigid post or am i wasting my time? Do i need to deconstruct the thing and repost with
6 x 6 ? Any suggestions would be helpfull.

06-22-2004, 09:34 AM
I would find some knee braces at your local home store. They should sell them in cedar in just about any size you want. They look very nice and are usually curved instead of just a straight brace.
The additional 4x4 probably won't do a whole lot and will probably make the post look off-center. If you were to try it I would use 2-2x4's - one on each side to even it up. It might work.

06-22-2004, 10:40 AM

Thanks for the quick reply. In reference to your idea of using the (2) 2 x 4 instead of the additional 4x4. Do i need to fasten the 2 x 4s to the deck frame and post or do i simply attach the 2 x 4s to just the post? Can i get away with using deck screws, or do i need something bigger like carraige bots or big lag screws?

Tom R
06-22-2004, 04:19 PM
Or you could wrap the 4X's with 1Xs on all 4 sides, overlapping your framing. It would strengthen in up and give it a 6 X 6 look. I always do it this way because 4 X 4's tend to look like 'matchsticks', when supportive.

06-22-2004, 04:50 PM
The only thing (in my opinion) that adding to the posts will do is just to make the wobbly posts into larger wobbly posts.

I think you need the diagonal braces at the top of the structure. You could buy 2x6's or 2x8's, then cut them into a nice curved shape with a jigsaw, scroll saw or bandsaw. Just attach them to the posts and top beam with long deck screws and you will be amazed how solid it will make your pergola.

As an example. whenever I build a gazebo, the diagonal bracing goes on before I ever attempt to do the roof since it really makes the whole structure go from jello-like to rock solid.

Tom R
06-22-2004, 05:01 PM
I agree he needs the corner bracing either way, but the reason I believe in his case adding to the posts would help (as long as it overlaps the framing) is because his 'weak (wobble) point' is where he 'notched' the 4 X 4. Now it's acting more like a 2 X 4. Otherwise, I generally do it for 'looks', not strength. (But then, I generally don't 'notch' the 4 X 4's).

06-23-2004, 06:17 AM
You guys are exactly right. I should have never notched the 4 x 4's. (Ah the pleasures of doing something for the first time). I am going to try the conservative approach and see if some bracing will make it feel sturdy enough. If that doesn't work, the next more radical approach would be to dissassemble the pergola and notch new 4 x 6 posts (it will be a 4 x 4 at the attachment points). I could then attach the posts to the deck frame as well as the deck posts. In addition i would run long pieces of blocking under the deck from post bottom to post bottom, which I would assume would create a pretty sturdy stucture, without ugly bracing.

THanks again for everone's help. If i ever build a second deck, it's gonna go so much smoother!!!!!!