ASCE 7-05 snow loading, calculating the snow load using the already-calculated Pf flat load, I am looking at the graph and trying to interpret from the sloped line, where the factor might be for a 12:12 pitch roof.
I am hearing that some copies of ASCE 7-05 have an error in that graph. Anyone care to give me the formula for the slope, so I can calculate it?
Looks like about 0.65 to me, which means if it is, the 1.5 factor then needed to adjust for unbalance due to drifting will put me right back at Pf, or for my location, 53.6 psf.
As an aside, the span tables are telling me I need, in SPF#2, 2x12s on 24 centers. The 1885 building being de-roofed for this remodel has rough sawn 2×6 rafters at about 20 inch centers, and has made it successfully through 120+ Adirondack winters so far.
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e=mc²(±1db)
Dinosaur
How now, Mighty Sauron, that thou art not brought
low by this? For thine evil pales before that which
foolish men call Justice....
SBCA (formerly WTCA) has an excellent spreadsheet for this and it's free. You just have to register.
It's called the Load Guide (towards the bottom of page) http://www.sbcindustry.com/loads.php
From another web page:
View Image
Attached is the errata sheet. Not sure of your question since the graph shows only straight lines so a formula is not really necessary. I assume you are aware there are 3 graphs depending on the thermal factor. 0.65 is about right for a warm roof using the solid line.