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ASCE 7 Reduction in Roof Live Load

ASCE 7 Reduction in Roof Live Load

ASCE 7 Reduction in Roof Live Load

If roof live loads are to act vertically on the projected surface, can you also use the R2 reduction in Eqn 4-2? Considering areas where snow would not control, this could be up to a 40% reduction in loading.

Eg. A roof with a 12:12 pitch (F = 0.6) and 20 psf roof live load could theoretically be reduced by 20*.707*0.6 = 8.5 psf.

RE: ASCE 7 Reduction in Roof Live Load

You CAN use R1*R2 to obtain the Roof Live Load reduction, but the total value of the multiplication is limited. The minimum roof live load is 12 sf. I don't have 05 in front of me, but in 10 the provision is 4.8.2.

RE: ASCE 7 Reduction in Roof Live Load

Yes you can, but the 8.5 psf load is applied along the slope not horizontally. So if your bearings are 10' horizontally apart. than your rafter is 14.14' in length. So you have the 14.14'(along the slope)*8.5psf equal to the 10'(horizontal distance)*12psf or 120 lbs. You will still have a 12psf minimum roof live load horizontally.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

RE: ASCE 7 Reduction in Roof Live Load

Yes 12 psf min

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