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Old 02-09-2015, 03:54 PM   #1
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Post Installation for 16x16 Pergola


Ok this will be the start of our Pergola build and I will document it here for anyone who would like to use in the future to maybe help them out. I have been researching the best way to install Pergola posts and most people are against burying the wooden post in concrete for fear it will rot in the future. I am now exploring the use of Sonotubes. Here is my question. We are excavating the Patio underneath where we are building the Pergola and will lay a concrete 6 inch Concrete foundation. Is it best to install the Sonotubes prior to the concrete patio, let it dry and then pour the concrete patio? Our posts will be 10 feet in height...so how far down should I bury the sonotubes? The dimensions of the posts are 8x8. Any help in this area is greatly appreciated.
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Old 02-09-2015, 04:53 PM   #2
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I don't really understand your use for sonotubes. Are your posts in the concrete or on top? Sonotubes are generally used for piers or if the hole you dig is too big and you want to save some concrete.
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Old 02-09-2015, 04:56 PM   #3
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You need to design all the structural elements of your pergola to carry the loads they will be subjected to. Loads are determined based on the geometry of the project, and the unit loads (typically taken from code). For example, if you are in the northeast, your pergola roof load (if there is a roof) will be controlled by snow loading. If you are in the south, roof load will be wind controlled. The loads are typically shown in the code which controls your design, your building inspector should be able to point you in the right direction.

Your posts need to support the vertical load (snow or wind), and also horizontal (wracking) load, typically due to wind, but could be seismic loading if you are in an earthquake area. If you bury your posts, the posts will carry shear load, and will resist racking. If you use galvanized brackets to support the posts on sonotubes, your posts need diagonal bracing in both directions to resist racking. In a house, wracking resistance is usually provided by plywood sheathing, but you don't have that in a pergola, so diagonal bracing is normally used (as in a deck).

If you use a metal bracket to support the post, the sonotube needs to be deep enough and wide enough to support the vertical load on the post. Width and depth are either code mandated (talk to your building inspector), or can be calculated based on the bearing capacity of your soil (your building inspector may be able to help you figure out the bearing capacity of the soil in your area).

If you don't need a permit, and there are no code requirements, you may want to see how a neighbor built their pergola, and follow a similar approach (assuming the neighbor's pergola worked out OK).
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Old 02-09-2015, 04:57 PM   #4
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Quote:
Originally Posted by qrod3 View Post
Ok this will be the start of our Pergola build and I will document it here for anyone who would like to use in the future to maybe help them out. I have been researching the best way to install Pergola posts and most people are against burying the wooden post in concrete for fear it will rot in the future. I am now exploring the use of Sonotubes. Here is my question. We are excavating the Patio underneath where we are building the Pergola and will lay a concrete 6 inch Concrete foundation. Is it best to install the Sonotubes prior to the concrete patio, let it dry and then pour the concrete patio? Our posts will be 10 feet in height...so how far down should I bury the sonotubes? The dimensions of the posts are 8x8. Any help in this area is greatly appreciated.
Ayuh,..... 1st off,.... Where are you, 'n what's the local frost depth,..??
'n what is the native soils,..??

The sonotube footers could be poured at the same time the floor coverin' 'em is poured,...
Or it could be done as a seperate pour, yer choice, little to no difference,...

Yer usin' steel, Right,..??

Last edited by Bondo; 02-09-2015 at 04:59 PM.
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Old 02-09-2015, 05:09 PM   #5
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We are in South Florida so not really worried about snow or frost. My big concern is hurricanes. I want to make sure we build this stable enough to withstand 150-170MPH winds. Will on top of sonotube or concrete be strong enough to support a 10 foot structure? Burying seems like the stronger solution, but I do not want the wood to rot away over time
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Old 02-09-2015, 05:19 PM   #6
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Originally Posted by qrod3 View Post
We are in South Florida so not really worried about snow or frost. My big concern is hurricanes. I want to make sure we build this stable enough to withstand 150-170MPH winds. Will on top of sonotube or concrete be strong enough to support a 10 foot structure? Burying seems like the stronger solution, but I do not want the wood to rot away over time
Ayuh,.... I believe the strongest connections is,....

Brackets welded to the rebar in the pour, 'n bolt the 6x6s to those,...
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Old 02-09-2015, 05:37 PM   #7
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I used pressure treated posts buried in concrete and wrapped them with cedar above ground. I went down about 2-3 feet and about 1.5 - 2 feet wide. I don't get the winds you get.
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Old 02-09-2015, 07:49 PM   #8
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OK, so you want to design for a hurricane. The uplift loads on the roof will be large, and depend on the type of roof and pitch of roof. You need to design your footers so the footers stay in the ground (don't laugh, I saw several pergolas that had blown away during Hurricanes Rita and Katrina, footers and all). You really need to discuss this project with your local building inspector, Florida building codes have gotten much tighter in the last few years, especially about wind loading. Your building inspector will have a good idea what is required for footers, posts, connections, framing, and roofing for your project. Footer types will depend on soil type in your area, which the building inspector should understand.
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Old 02-11-2015, 02:00 PM   #9
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Originally Posted by Daniel Holzman View Post
OK, so you want to design for a hurricane. The uplift loads on the roof will be large, and depend on the type of roof and pitch of roof. You need to design your footers so the footers stay in the ground (don't laugh, I saw several pergolas that had blown away during Hurricanes Rita and Katrina, footers and all). You really need to discuss this project with your local building inspector, Florida building codes have gotten much tighter in the last few years, especially about wind loading. Your building inspector will have a good idea what is required for footers, posts, connections, framing, and roofing for your project. Footer types will depend on soil type in your area, which the building inspector should understand.
Ayuh,.... I know I ain't wordy enough in my posts, but this is the Point of my sayin',......
"Brackets welded to the rebar in the pour, 'n bolt the 6x6s to those,..."
As in doin' so, the entire patio will become ballast,...
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Old 02-11-2015, 02:43 PM   #10
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Bondo made a good suggestion.

Also you could inbed something like these Tees into the concrete foundation. It then would be bolted to the sides of 6x6, the 6x6 would still need the feet to rest on.

http://www.amazon.com/gp/product/B00...d_i=B0044FR5Q4



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