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RodBarnes 07-26-2012 05:26 PM

Patio awning design check
 
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I am in the process of designing an awning for our patio. The patio is a 12'x24' concrete pad. The awning will be attached to the house (brackets on a ledger board) with four 4x4 posts at the other end.

Using www.awc.org (calculator for rafters) I determined that I should use at least 2x6, 16oc, #2 (non-incised) Dougals Fir to cover the 12' span between the ledger and the posts. This is based upon a 20psf snow-load (which is actually more than the 10psf spec'd for my location), 10psf dead load, and L/240 deflection. The "inch-per-foot" rule implies I would need an 2x8 header.

But I plan to use corrugated fibreglass or other synthetic panels for the roof so the dead load would be significantly less than with standard construction.

So I'm wondering if this is overkill or seems right. I'd appreciate your feedback before I proceed.

I've attached a shot of my design from Sketchup.

tony.g 07-27-2012 04:20 PM

The 2x6s spanning from the house wall to the main bearers across the posts would be OK (2x8s would be unnecessary).
Your main problems will be fixing the main bearers to the posts, and then the joists to the main bearers, allowing for wind uplift, as these roofs are very light. Simpson do special fixings for this

RodBarnes 07-27-2012 04:31 PM

I plan on using hangers on both ends of the joists screwed into the ledger and main bearers. Likewise, I plan to use similar connectors with screws to attach main bearers to posts. Posts will be bolted/screwed into post brackets which are already embedded in concrete when I had it poured. Screws will attach roof panels to strips across joists.

GBrackins 07-27-2012 06:26 PM

Rod,

sounds like you've put a lot of thought into your design. Wind loads need to be addressed as you are building basically a sail. Your location determines wind loads. Where are you located?

RodBarnes 07-28-2012 05:51 PM

Located in NW Oregon. We don't get a lot of significant wind. Maybe a windstorm one or two times a year that gust to 40+. Rarely more -- such as the Columbus Day storm of 1962. I was a kid then and remember it but that is the rare case where even house roofs had problems. There are plenty of awnings around similar to what I want to build and they've all survived.


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