The fact that snow loads only act part of the year has been used to create the rafter tables.
Live load for roof pitch tables.
The loads are based on adjusted roof snow loads from the governing building code.
If your code book says your snow load is 40 psf then you use the 40 psf live load rafter table.
For example in the rafter span table below the highlighted cell in the 40 live load table indicates that 2 x 8 southern yellow pine joists that have a grade of 2 that are.
2attic loads may be included in the floor live load but a 10 psf attic load is typically used only to size ceiling joists adequately for access purposes.
The snow load is treated as a live load when you use af pa s tables.
Total load psf duration factor live load psf roof type 55 1 15 40 snow shingle 55 1 15 30 snow tile 47 30 snow 40 20 snow 1 25 20 construction or rain not snow load 55 1 15 40 snow.
Ground snow load might seem somewhat confusing until you read the basic premise that is identified in irc section r301 6 which states.
The shapes and spans shown here represent only a fraction of the millions of designs produced by alpine engineers.
The roof must be able to support the sum of its dead load and any anticipated live load so the roof has to be designed with a load limit that takes into account both of these loads.
1607 12 1 distribution of roof loads.
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.
Visit the roof framing page for more information on cutting roof rafters and visit the roof pitch calculator for determining rafter lengths based on rise and run.
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.
For roof live loads of 12 psf or 16 psf.
The roof shall be designed for the live load indicated in table r301 6 or the snow load indicated.
Loads should be determined in accordance with this chapter.
Roof loads rafter spans are tabulated for the most common roof loads.
This information is found in the code book.
Span configuration and load conditions.
This issue of live load vs.
However if the attic is intended for storage the attic live load or some portion should also be considered for the design of.
Victor staley a building official in the town of brewster mass responds.
Roof live loads largest roof loads typically caused by repair and maintenance pitch rise span lr 20 r1r2 12 lr 20 lr horizontal projection roof live load 16 r 1 r 2 live load reduction factors r 1 accounts for size of tributary area of roof column a t r 2 effect of the roof rise.
