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 4×4 posts at the other end.
Using www.awc.org (calculator for rafters) I determined that I should use at least 2×6, 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 2×8 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 attached a shot of my design from Sketchup but it isn’t appearing for some reason.)