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CuriousHomeowne 04-14-2012 07:38 PM

Wood shade structure beam requirements
 
I am having someone build a wood shade structure in my back yard and I am concerned about the size of the beam they are using.

The size of the structure will be 22 x 9 and only have the four posts in the corners. They are currently set to use a 6 x 6 beam that is going to span the entire 22 feet.

I am concerned that it will not be sufficient throughout the short term to prevent sagging. Any knowledge on the subject would be helpful.

Thanks,

Joe Carola 04-14-2012 07:46 PM

Quote:

Originally Posted by CuriousHomeowne
I am having someone build a wood shade structure in my back yard and I am concerned about the size of the beam they are using.

The size of the structure will be 22 x 9 and only have the four posts in the corners. They are currently set to use a 6 x 6 beam that is going to span the entire 22 feet.

I am concerned that it will not be sufficient throughout the short term to prevent sagging. Any knowledge on the subject would be helpful.

Thanks,

Do you have approved plans and permits? Is the contractor licensed and insured?

cortell 04-14-2012 08:13 PM

I can almost guarantee you that's going to sag like crazy. A neighbor down the street from me has a pergola with 2x6 beams. They only span about 10 ft and it has a huge sag. 22' is a ridiculous span for a 2x6. I'd bet it would sag under it's own weight.

If I were you, I'd get a very detailed description of exactly what they're going to do and post it here for review. Eg what are the beams going to support? How were the posts laid? 22' seems unlikely. I'd be surprised if they can get a 2x6 longer than 20'.

We need more details to tell you just how alarmed you should be about the whole project

cortell 04-14-2012 08:16 PM

I said 2x6 though you said 6x6. Doesn't matter. I contend a 2x6 will sag on it's own over that span. Whether it's 2x6, 4x6 or 6x6...the baseline sag will be identical

CuriousHomeowne 04-14-2012 09:18 PM

Joe - yes there are plans and permits. They also are licensed and bonded. However, that does not reassure me n this point :)

Cortell - I would agree. That is why I was wondering. Thanks for the comment.

The beams are only going to be supporting the beams themselves and a canvas cover.

Daniel Holzman 04-15-2012 06:06 AM

Cortell, the sag from a 2x6 is totally different than the sag from a 4x6 which is different than the sag from a 6x6. This derives from fundamental mechanics of materials principals.

The required size of a beam depends on the load, the dimensions of the beam, the span of the beam, and the connection details from the posts to the beam. The required load depends on your location, and is usually code driven.

The OPS has stated that they filed for and received a permit, and that the contractor is licensed. Presumably the design was either taken from a previously approved set of plans, or the design was done by a licensed designer and approved by the code authority. If the OPS now is having second thoughts about the adequacy of the design, the simplest place to start would be with the contractor, or hire and engineer or architect to review the plans. Attempting to review plans for a relatively large structure over the internet is just a recipe for confusion, you are likely to get uninformed opinions based on anecdotal comparisons to projects that likely have nothing to do with your specific situation.

cortell 04-15-2012 11:41 AM

Daniel, with all due respect, I'm not sure you got my point. For a given external non-trivial load, the sag in a 2x6 will for sure be greater then the sag in a 6x6. My point was that in absence of an external load, the sag of a 2x6 and 6x6 will be the same. If you claim that not to be true, please enlighten me with an explanation.

I call this the baseline sag, or the "minimum" sag. If the baseline sag of a x6 over 22' is visually unappealing, it makes no difference what the load is, or whether it's a 2x6 or 6x6. The customer is not going to like the end result.

Also I strongly disagree with your commentary. Permits and inspections are all about meeting MINIMUM code. Minimum code is almost entirely about safety. That process will help ensure the structure will not fail. It will not ensure the customer gets a visually pleasant result. The OP's question was about sag; it was not about safety. Pinging the discussion board on opinions about whether something will look good is entirely appropriate.

cortell 04-15-2012 11:46 AM

Also I acknowledge the comparison to my neighbors pergola was off base; I misread the OP's post. I quickly revised my position, though my verdict remained the same ( for reasons I've already explained)

PaliBob 04-15-2012 01:33 PM

My concern would be the strength of the posts connection to the Shade Structure and the strength of the posts connection to ground.
In a storm condition you may have a 200 sq ft SAIL!

edit: oops now I see in post #5 that the cover will be canvas
.........I assumed it would be a solid material

House Engineer 04-15-2012 05:32 PM

If the top is covered, remember to design it to support enough live load.

With a structure like you describe, I would build in some extra capacity to give the structure long-term outside durability and to be able to support the Adirondack swing that your wife will want you to hang from that 6x6. (Don't use the 6x6. It is grossly undersized).


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