Ground snow load might seem somewhat confusing until you read the basic premise that is identified in irc section r301 6 which states.
Live load for roof pitch tables.
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.
If your code book says your snow load is 40 psf then you use the 40 psf live load rafter table.
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 follow ing table.
Loads should be determined in accordance with this chapter.
The fact that snow loads only act part of the year has been used to create the rafter tables.
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.
Span configuration and load conditions.
This issue of live load vs.
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.
Roof loads rafter spans are tabulated for the most common roof loads.
The roof shall be designed for the live load indicated in table r301 6 or the snow load indicated.
The shapes and spans shown here represent only a fraction of the millions of designs produced by alpine engineers.
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.
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.
The loads are based on adjusted roof snow loads from the governing building code.
The loads are based on adjusted roof snow loads from the governing building code.
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.
1607 12 1 distribution of roof loads.
This information is found in the code book.
For roof live loads of 12 psf or 16 psf.
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.
