Roof Live Load Reduction Formula

The live loads for members supporting two or more floors are permitted to be reduced by a maximum of 20 percent but the live load shall not be less than l as calculated in section 1607 10 1.

Roof live load reduction formula.

One for the tributary area supported by the structural element r 1 and the other for the slope of the roof surface r 2. You can also find the load per square meter or square foot of roofing by opening the advanced mode. Where l r shall not be less than 12 psf and not more than 20 psf. R2 is a reduction factor for roof slope above 4 12.

Where snow isn t a problem the live load can come from people working on the roof and any equipment they. I am looking at irc2009 don t have irc2006. If the roof design load is 20psf and you are considering the compression in a web member that is located near the mid span than i would not use live load reduction for the compression in that member. Where d is floor dead load.

I ignore the slope factor altogether for snow load reduction which adds another measure of conservatism. However in my practice i typically use the horizontal run of the roof for both types of load. L r l o r 1 r 2. Roof live load reduction.

The equation in the ibc is lr lor1r2. The op s question was with regards to live load and you are referring to roof live load. Roof live load may be reduced by the following equation. Also table r301 7 is for allowable deflection of structural members.

If you want to calculate these values by hand use the following formulas. R 1 1 for a t less than or equal to 200 psf r 1 1 2 0 001 a t for between 200 psf and 600 psf. Snow load is different than roof live load. T 1x 300 300 sq ft 400 no live load reduction permitted.

Once you know these values our snow load calculator automatically finds the total weight of snow on your roof. Live load reduction is a reduction in live load that contributes to the actions on a member. Snow load thickness density. The reduction formula has two reduction terms.

The commentary in asce 7 05 c4 about roof live load reductions explains the anticipated difference in use of roof areas vs. R1 is for tributary area above 200 sq. No where it talks about any reduction is live load unless i am missing something. For uses other than storage where approved additional live load reductions shall be permitted where shown by the registered design professional that a rational approach has been used and that such.

They are not one and the same. To do this i use conservative too heavy dead loads and full snow loads regardless of pitch.