Pergola Wobbly

[utabusdriverslc]

We have just helped a relative build a 23'x13'x10' pergola. It is not attached to the house. It is quite wobbly. We're not sure if it's because of the post bases, or because of the post caps, or because it doesn't have enough support. Everything is put together with screws, except for the lower 2x6s. We are amateurs at this and would appreciate any kind:thumbsup: suggestions.

 

[boomer1025]

Poles should have been heavier which would have helped some.

 

[ustmd]

When you say "wobbly", could you be more specific. Does it move side to side (i.e. parallel to the house) or is in all directions?

 

[ace10]

Many, many issues there.

Everything.... every single piece of wood appears to be undersized. 4X4 posts are simply not up to the task. You needed 6X6s. Using 4X4's for your beams was another really bad idea. Possibly the worst in the whole thing. Your 2x4 diagonal braces aren't providing any meaningful assistance. It looks like you used furring strips for your purlins.

You're not going to want to hear this, but if I was asked to "fix" that structure, I'd begin by carefully taking it down and starting over.

You tried to do it on the super-cheap.

6X6 Posts. Shorter. No reason for that structure to be so tall.
Triple 2X10 or 2X12s for the beams.
4X6 for the diagonal bracing. Bolted through the posts all the way into the brace on the other side.
The rafters should be 2X8 or 2X10. Some might tell you 2X12. Especially on 24" centers.
The purlins should be 2X4's.

You can reuse the tins.

Do it all in PT or some other resistant wood stock.

This is all my opinion. Others might tell you different. $0.02

 

[AchingBack]

Many, many issues there.

Everything.... every single piece of wood appears to be undersized. 4X4 posts are simply not up to the task. You needed 6X6s. Using 4X4's for your beams was another really bad idea. Possibly the worst in the whole thing. Your 2x4 diagonal braces aren't providing any meaningful assistance. It looks like you used furring strips for your purlins.

You're not going to want to hear this, but if I was asked to "fix" that structure, I'd begin by carefully taking it down and starting over.

You tried to do it on the super-cheap.

6X6 Posts. Shorter. No reason for that structure to be so tall.
Triple 2X10 or 2X12s for the beams.
4X6 for the diagonal bracing. Bolted through the posts all the way into the brace on the other side.
The rafters should be 2X8 or 2X10. Some might tell you 2X12. Especially on 24" centers.
The purlins should be 2X4's.

You can reuse the tins.

Do it all in PT or some other resistant wood stock.

This is all my opinion. Others might tell you different. $0.02

Perhaps the height of the structure is to keep the hot air higher. One problem, and a big one, the post brackets are too small to accommodate a 6"x6" post.

 

[ace10]

Perhaps the height of the structure is to keep the hot air higher. One problem, and a big one, the post brackets are too small to accommodate a 6"x6" post.

Cut off the 4X post brackets, then drill holes for new ones. Secure with epoxy.

 

[dave1949]

Yes, there are issues.

Supposing the goal is to improve what is there, you could add some rigidity by boxing in the ends above the double 2x6's, tying that to an added pair of purlins running at the top of the posts. You could do the same across the long dimension too. That space isn't really accomplishing much now. If you use pt plywood 4x8 sheathing for strength, then cover it with something that looks good, matches the house siding maybe.

One concern I have is the roof doesn't appear to have much slope. I doubt you worry about snow loads, but a heavy rain needs to run off easily too. The roof as it is, is not providing much in the way of stiffening the structure, due to the furring strips and tin being all there is there. Is there a plan to finish the underside of the roof?

 

[jaotguy]

one thing to try ....

screw a long 2 x 4 ( 2 screws per rafter ) to the bottom of the roof , run it on the diagonal ( corner to corner ) ... it should help stiffen the "roof box area " and prevent shifting side to side
........... walls have very little strength until they are sheathed , same with the roof design in the picture.

the other suggestion is to prop up each end ( corner ) , remove the end post and sonotube footing ... pound in a bigger steel pipe and keep 2 feet above ground showing ... slip the end post back ( inside the new tube ) reconnect to structure, then fill the voids with cement to take up any slack space and set the proper height ..... let it cure completely .... then do the same to each of the remaining corners .....


right now , the structure is just a couple of post sitting ON the ground ... by putting a base in the ground and UP the posts, you increase the side load capability ....

 

[utabusdriverslc]

Thanks to all that replied.
We're going to strengthen the front and back with additional 2x6s and are considering 2' of addional cement around the footers.
The roof has vinyl corrugated panels. We're going to add a different type of bracket to the 2x6 rafters. We feel that many of the brackets we used were the wrong type, particularly the 4x4 post caps.

 

[tcreeley]

We have just helped a relative build a 23'x13'x10' pergola. It is not attached to the house. It is quite wobbly. We're not sure if it's because of the post bases, or because of the post caps, or because it doesn't have enough support. Everything is put together with screws, except for the lower 2x6s. We are amateurs at this and would appreciate any kind:thumbsup: suggestions.

Your rafters need bridging straps or blocks - criss crossing between them. That would tie them to each other and make them roof work as a unit. Now each rafter is independent of the other- leads to flex.
Your structure is prone to twist and rock, and fold like a hinge. You need more diagonal bracing - on all 4 sides, especially as your posts are in effect free standing. Think of how trusses work- triangles, one after the other, that work together.
Put some diagonal/triangle/truss like bracing in - use plywood to lock it together, more the better.

- Looking at it more, and the car port plans that are similar, the big difference I see is that you don have any sheathing on the rafters, so they work independently of each other and don't contribute much to the rigidity. I'd target that with bridging-wood or metal. I think that would tie most of it together. On the two ends- some triangle bracing up and down from the rafter to the side beam- to get rid of the hinge effect. If you used timbers -6x6's etc, this would be less of a concern. You have plenty to work with,
Good luck.
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