Roof Design For Heavy Snow Load

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.

Roof design for heavy snow load.

Proper roof ventilation and high r value roof insulation is essential to minimizing ice dam formation. It includes formulas for calculating snow design loads for various locations and roof configurations. In some cases roof snow melt systems or heat tape can be used to combat ice accumulation on eaves and in valleys. 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.

This includes overhangs and multiple roof levels. Roof load live load design is affected by the shape of the roof whether it is flat curved or pitched. 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. However a south roof load zone home cannot be installed in either a middle or north roof load zone.

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. Or the 25 psf snow load could be entered as a roof snow load with the unbalanced snow loading option turned off. Hipped roofs are often used in complex roof formations with the hips facing different directions. First figure out how deep the snow is piled up there.

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. Roof loads are a downward vertical force on the home.

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. 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. The north zone middle zone and the south zone are identified on the roof load zone. Snow loads are influenced by elevation general weather and moisture patterns slope direction exposure roof or trail bridge configuration and wind direction and severity.

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. Generally loads get higher where more snow falls when roofs are shallower rather than steeper and where drift loads can accumulate. Express the result in feet rather than inches. Framing table for maximum roof rafter spans.