helena
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# Posted: 30 Jan 2013 06:15pm
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Trying to figure out my rafter and roof beam sizes. On little buildings I "guess" and then beef up a bit but, this I'm going to be sleeping under and we had hurricane force winds last night that got me paranoid! 
Building is 20' x 20'. I'm going the pole construction route so, have buried 9 - 6x6 posts 3 and half feet in the ground. So, I have spans of 10 feet every direction.
I'm doing a turf roof and have figured out the following for my loads:
Turf fully rain saturated - 1" depth of turf = 7 lbs. per square foot
I will be cutting turf 2-3" thick so make it 21 lbs. per square foot
Is that my total DEAD load or do I need to factor in weight of sheathing/sarking and rafters?
How do I figure out my LIVE load? Are environmental loads calculated in as the LIVE load?
My worst case scenario environmental loads are:
SNOW LOAD:
1" inch snow = 1.25 lbs. psf
20" inches snow = 25 lbs psf
WIND LOAD:
I calculate the strongest wind to be 120 mph.
Calculating windspeed to pressure (.00256 x V2) V=120 mph
.00256 x 14400 = 36.86
with the addition of "drag coefficient" for flat square surfaces you multiply above x 2.
36.86 x 2 = 73.73 lbs. psf
So, total environmental load, worst case scenario is roughly 100 lbs psf!
How do I factor in the environmental loads of snow and wind?
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