Sun shade over elevated deck...will this work?

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Old 05-21-12, 01:51 PM
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Sun shade over elevated deck...will this work?

I have an 12W x 10L elevated deck that sits about 5.5 to 7 feet above gound that is in need of some shade.

I would like to build a free standing support structure (similar to a pergola frame) to hold a sun shade/sun fabric.

Would this be adequate to support it (since it only has to hold the weight of the lumber?):

1. 4x4 post attached to current deck rail post (shown in pic) and rim joist using carriage bolts through joist and lag screws through posts.
2. 4x4 post attached to deck joist below using carriage bolts (for post located near door/house)
2. Double (or single?) 2x6 beams, running front to back, bolted to posts
3. 2x6 rafters spaced 24" OC running, side to side
-or-
2x4 rafters spaced 12" OC with/without 2X4 or 1x4 purlins spaced 12"

Overall, would be 137" wide and 124" long between posts. Can only use 4 posts due to the window that's in the way...I know this is a big span between posts, but since the only weight is lumber, would I be okay?

A picture is attached.

Would this work? Better suggestions if not...

Thanks in advance.
 
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Old 05-25-12, 09:48 PM
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What you're planning to do could work, keeping a few things in mind.
1. Spanning 10' with 2 x 6 beams will result in the beams developing a sag over time (even though the loading is minimal). Same for the 12' joists. You might consider increasing the stiffness of beams and joists by adding bottom "flanges" (2 x 4s oriented in the flat direction), glued and screwed. The effective beam spans could be reduced by installing 2'-offset corner braces (through-bolted, at 45 degrees) at each end. Would add an interesting look, too.
2. Bolting through existing rail posts to attach your corner columns could be "iffy", unless they are super-tightly attached to the deck's structure with through-bolts, blocking and brackets. If the existing rail posts wiggle when pushed firmly, they aren't suitable for attaching columns to. Adding holes will also weaken the posts somewhat.
3. If you live in snow country and have a fabric cover over the finished framework, that's a whole new ball game in terms of applied loading. Speaking from experience here--we had a cheapo patio gazebo completely collapse a few years ago during a freak snow storm. I had been sweeping the heavy, wet stuff off about every half-hour or so, but it wasn't enough to prevent the steel 1" square tubes from buckling.
4. In addition to snow loads, wind loading will also exert some serious pressure on the structure. Think of a big sail, catching a 60 mph or 70 mph updraft against the house.
 
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