Roof Design For Heavy Snow Load

Roof loads are a downward vertical force on the home.

Roof design for heavy snow load.

Shed dormers are easier to waterproof and shed snow better than gable dormers. The north zone middle zone and the south zone are identified on the roof load zone. Proper roof ventilation and high r value roof insulation is essential to minimizing ice dam formation. Express the result in feet rather than inches.

Generally loads get higher where more snow falls when roofs are shallower rather than steeper and where drift loads can accumulate. This includes overhangs and multiple roof levels. 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. However a south roof load zone home cannot be installed in either a middle or north roof load zone.

First figure out how deep the snow is piled up there. Or the 25 psf snow load could be entered as a roof snow load with the unbalanced snow loading option turned off. 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. The balanced snow load is applied everywhere where the roof structure is located.

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. 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. It includes formulas for calculating snow design loads for various locations and roof configurations. 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.

Hipped roofs are often used in complex roof formations with the hips facing different directions. 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. Roof load live load design is affected by the shape of the roof whether it is flat curved or pitched. In some cases roof snow melt systems or heat tape can be used to combat ice accumulation on eaves and in valleys.

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. 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. Framing table for maximum roof rafter spans. 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.