Pergola - Questions about general approach and posts on brick patio.


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Old 02-26-10, 10:31 PM
J
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Pergola - Questions about general approach and posts on brick patio.

Hello all,

My wife and I are planning on building a pergola. I'd like to describe our planned approach to see if there is anything silly we are doing and then ask some specific questions.

The footprint we are looking at is approximately 7' by 40'. We were planning on 4x4 redwood posts and 4x4 redwood beams. We have a solar screening mesh we are using for the top cover so the load on the beams should be minimal, as there are no slats. Our longest planned unsupported beam span is 12' between posts. I'm not sure if this is too long or not. My hand calculations show a maximum 1/4" droop assuming a 20 pound load evenly distributed. We have a porch cover with a stuccoed over 4x6 (maybe 4x8) beam that we would like to support one side (the 40' side) of the pergola from. We plan to have 4x4 knee braces on each side of the post to its attached beams.

The biggest question I have is anchoring the posts. The surface we are building the pergola on is a red brick patio. It has a 1/8" per foot slope. My wife is adamant that we won't remove any bricks and pour footers. Desire is to do nothing that would prevent us returning directly to a pre-pergola state by removing the pergola. I'm stumped. If it matters, we're in southern Arizona. We get short lasting heavy rainstorms in the summer and are not generally concerned with frost lines. Digging in the caliche filled soil is no picnic.

The options I can think of are:

1) Just have the posts directly on the bricks

2) Build a cement form on top of the bricks and pouring a "footing" in that, casting a strong-tie post base in it. It's not as good as a footing in the ground but it could be pretty massive.

3) Stack a few 14"x14" pavers on top of the brick pavers and lag bolt a concrete post base to them.

Also, I don't know how to deal with the slope of the bricks as it transfers to the posts. Of course this will depend on how I do the post bases. Do the bases have a little play in them so I can plumb and level the posts even if the base is slightly sloped?

Thank you VERY much for your time.

Looking forward to a successful project.
- Jason
 
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Old 02-27-10, 04:45 AM
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Welcome to the forums! Adamancy (sp) quite often extinguishes possibilities of progress. Picture this....if you don't dig footings and properly apply the vertical posts, preferably at 8' spacing, and you install the screening on top, you have a high wind with your rain storms, you basically have a parachute that will take your pergola into the neighbor's yard and collapse it like a deck of cards.
So option 1) No
Option 2) won't allow you to go back to pristine brick
Option 3) won't prevent vertical lift.

Dealing with the slope will just entail making each post at 8' interval 1" longer, but better yet, level across the top, regardless of the projected slope, which is sometimes variable.
Hang in there, we have a bunch of seasoned deck folks that will chime in with other viewpoints. I gave you mine, and it was free and worth every penny of it.
 
 

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