R301.6

Section R301.6 is titled 'Roof load' and covers the requirements for the design and construction of a structure taking roof live loads into consideration. The method for determining roof live load and use of roof live load or snow load, whichever is greater, for roof design is established. The method for determining roof live load is by reference to a table which has 3 rows of different roof slope ranges and 3 columns of different tributary load ranges, with the table data listing the required design load. The purpose of this section is to prevent structural failure.

The model shows 3 roofs built with ridge beams and rafters 16" on center, each roof having a highlighted structural member with a corresponding translucent plane above it, which represents the member's tributary area. The following examples presume that these roofs are built in a location that snow load would not exceed roof live load.

The left roof has a slope that is less than 4-12 and a 20' span with a highlighted rafter. Using the table, the intersection of the 1st row and 1st column requires the rafter to be designed at 20 lbs/sq ft. The middle roof has an 8-12 slope, 20' span, and a length of just over 40' with the ridge beam highlighted. Using the table, the intersection of the 2nd row and 2nd column requires the ridge beam to be designed at 14 lbs/sq ft. The right roof has a 12-12 slope, 30' span, and a length of just over 40' with the ridge beam highlighted. Using the table, the intersection of the 3rd row and the 3rd column requires this ridge beam to be designed at 12 lbs/sq ft.