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Old 04-06-2011, 09:01 PM   #1
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Will My Pergola Beam Sag?


Hey Guys,

I'm looking to build a Pergola frame (no rafter or purlins) around my fire pit. I'd like one of the sides to span 18' using a 2X10X20. Will I run into issues with this saging or twisting down the road? I could use cross pieces on top to join the two 2X10X20 together if needed to stop flex/twisting. I guess my biggest conern is saging.

Also what type of footing would you recommend for the 6X6 (I like the larger post look vs a 4x4) posts? Some say a concrete footing with a simpson anchor, others say to put the beam in concrete directly in the hole. The beams will be surrounded by a paver patio and also have 3x2 columns (each side) built on the bottom for looks, so water isnt going to be an issue. I could use copper bands at the footing and where the column cap will meet the 6x6 if needed

What do you recommend?

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Old 04-06-2011, 10:50 PM   #2
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Will My Pergola Beam Sag?


By the way I am in Houston, Texas.

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Old 04-06-2011, 11:57 PM   #3
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Will My Pergola Beam Sag?


If you're using pressure treated, #2 grade southern yellow pine, you'll need 2x12 to span 18 feet.
I would design it so the span was reduced.
Ron
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Old 04-07-2011, 01:53 AM   #4
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Will My Pergola Beam Sag?


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Originally Posted by Ron6519 View Post
If you're using pressure treated, #2 grade southern yellow pine, you'll need 2x12 to span 18 feet.
I would design it so the span was reduced.
Ron
Hey Ron, how did you figure that one? Even with a live load, of which there is none, of 10 lbs. and assuming a dead load of 10 lbs. I came up with a span of over 23'.

Thank you sir.

Andy.
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Old 04-07-2011, 08:31 AM   #5
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Will My Pergola Beam Sag?


If I understand you correctly, you want to build a frame but no roof. Unless you are planning to support something on top of the joists, the only load will be the weight of the joist itself. But maybe I don't understand what you are proposing.

If there is no live load, weight only, the issue will not be sag, but twist of the wood as it dries. Very hard to get PT lumber that is dry, it is usually at least 30 percent moisture content, and it is likely to twist and bend as it dries. If this is aesthetically unacceptable, you need to get LVL or microlam, not for strength, but to resist twist.

As for the footings, you live in Houston, famous for expansive clay soil, which is a real problem for shallow footings. You should check with your local building inspector, they may have some suggestions for low load footers to minimize soil movement.
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Old 04-07-2011, 08:48 AM   #6
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Will My Pergola Beam Sag?


I looked up a few things regarding your area and it seems to me that for this project (if I understand the scope) you may not need a permit.
I would look into cedar and footings of 12" dia. sono-tubes about 24" min. deep would work fine.
Lots of other details too but that is a start.

Andy.
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Old 04-07-2011, 10:28 AM   #7
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Will My Pergola Beam Sag?


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Originally Posted by AndyGump View Post
Hey Ron, how did you figure that one? Even with a live load, of which there is none, of 10 lbs. and assuming a dead load of 10 lbs. I came up with a span of over 23'.

Thank you sir.

Andy.
I looked it up in a span table.
Ron
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Old 04-07-2011, 10:27 PM   #8
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Will My Pergola Beam Sag?


Thanks for the input guys!

There is no load on the pergola besides the weight of the frame itself, in this case (2) 2X10X20 on each side (the long spans). The shorter spans will use (2) 2X10X16 cut to lenght. that's it.

I can get blue linx 2.0E LVL for $50 (2X10X20) if that would be a better option? I plan on coating the entire structure with an exterior finish in a cedar color to protect it (and for looks), so if it isnt treated wood it isnt a huge deal.


I also could move up to 2X12 if needed?


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Old 04-16-2011, 12:27 PM   #9
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Will My Pergola Beam Sag?


I did a pergola with a 16' span with 2x6's a while back and used douglas fir. I only got warping in one piece but was able to bend it back and fasten it. I t looks fine.
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Old 04-16-2011, 12:51 PM   #10
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Will My Pergola Beam Sag?


Missed the opening post. No comment.

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