Roof Design For Heavy Snow Load

If unbalanced snow loading isn t required or specified the truss designer may enter the 25 psf snow load as a top chord live load tcll set the load duration factor to 1 15 for snow and turn snow loading off completely.

Roof design for heavy snow load.

Shed dormers are easier to waterproof and shed snow better than gable dormers. If the design necessitates a roof slope that drains onto a traffic area snow retention devices should be provided to hold the snow in place. Snow loads are influenced by elevation general weather and moisture patterns slope direction exposure roof or trail bridge configuration and wind direction and severity. Depending on your region you may need to design for a maximum snow load of anything between zero to 65 pounds per square foot or roughly 0 3 kpa.

This includes overhangs and multiple roof levels. After you obtain the roof slope factor from those sections in asce 7 10 the balanced design snow load for the sloped roof can easily be calculated using equation 7 4 1. The easiest way is to push a yardstick into the snow on the roof selecting an area that looks typical of the overall snow depth. Framing table for maximum roof rafter spans.

These distinctive roofs with overhanging eaves feature four medium pitched sides and are characteristic of dutch architecture and help disperse snow loads in northern climates. Proper roof ventilation and high r value roof insulation is essential to minimizing ice dam formation. A great deal of confusion currently exists among engineers architects recreation specialists and maintenance personnel concerning the proper snow loading to use for the design and maintenance of trail bridges building roofs and other structures in mountainous high snow load areas. Let s look at the sample table below which shows maximum rafter spans for a snow load of 31 3 pounds per square foot psf.

For example 18 inches would be 1 5 feet. The balanced snow load is applied everywhere where the roof structure is located. Hipped roofs are often used in complex roof formations with the hips facing different directions. Roof load live load design is affected by the shape of the roof whether it is flat curved or pitched.

Roof loads are a downward vertical force on the home. Instead they reference asce 7 a specification published by the american society of civil engineers and the structural engineering institute called minimum design loads for buildings and other structures. If you live in the us our snow load calculator compares the total weight on your roof with the permissible load calculated according to the standards issued by the american society of civil engineers regarding the minimum design loads for buildings and other structures asce7 16. In some cases roof snow melt systems or heat tape can be used to combat ice accumulation on eaves and in valleys.

First figure out how deep the snow is piled up there. The north zone middle zone and the south zone are identified on the roof load zone. Express the result in feet rather than inches. Or the 25 psf snow load could be entered as a roof snow load with the unbalanced snow loading option turned off.