Roof Live Load Less Than 20

Roof live load may be reduced by the following equation.

Roof live load less than 20.

For roof live loads of 12 psf or 16 psf. Where l r shall not be less than 12 psf and not more than 20 psf. In my region on cape cod we have a ground snow load design of 25 psf which is a greater design load than the live load 12 psf to 20 psf over an entire roof system. For roof live loads less than 20 pounds per square foot psf rafter spans and required e values tabulated for 20 psf shall be permitted to be adjusted in accordance with the fol lowing table.

Where uniform roof live loads are reduced to less than 20 psf 0 96 kn m 2 in accordance with section 1607 13 2 1 and are applied to the design of structural members arranged so as to create continuity the reduced roof live load shall be applied to adjacent spans or to alternate spans whichever produces the most unfavorable load effect see section 1607 13 2 for reductions in minimum roof. Many factors influence how a system responds to loading. 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. Where uniform roof live loads are reduced to less than 20 psf 0 96 kn m2 in accordance with section 1607 12 2 1 and are applied to the design of structural members arranged so as to create continulty the reduced roof live load shall be applied to adjacent spans or to alternate spans whichever produces.

For example appendix a indicates that one type of clay tile roof system has a live load value of 20 psf and a dead load value of 15 psf. Where uniform roof live loads are reduced to less than 20 psf 0 96 kn m 2 in accordance with section 1607 12 2 1 and are applied to the design of structural members arranged so as to create continuity the reduced roof live load shall be applied to adjacent spans or to alternate spans whichever produces the most unfavorable load effect. L r l o r 1 r 2. Af pa s appendix a lists a variety of live and dead load combinations for floors ceilings and rafters.

Factors that influence. On a roof with a slope greater than 4 to 12 the live load limit is typically adjusted downward from 20 psf to 15 psf to allow for the relatively greater dead load on the steeper roof. R 1 0 6. Roof live load of 20 psf or less see ibc 1607 and chapter 3 of this publication r rain load see ibc 1611 and chapter 3 of this publication s snow load see ibc 1608 chapter 7 of asce sei 7 and chapter 4 of this publication t cumulative effects of self straining forces and effects see asce sei 2 3 4 and 2 4 4 w load due to wind pressure see ibc.