Flat Roof For Snow Load

Another is that they cannot handle as much snow weight as pitched roofs because the snow sits directly on the roof.

Flat roof for snow load.

Minimum flat roof snow load values. Lets assume our project is in madison wisconsin and we have already calculated our balanced roof snow load here. 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. The snow load that is applied to our structure is not the ground snow load but in most cases the flat roof snow load.

You need to use a snow load formula for flat roofs. In regions with relatively low snow load values the load from a single event may result in the peak loading. The flat roof snow load is calculated using formula 7 3 1. First figure out how deep the snow is piled up there.

For ground snow loads greater than 20 pounds per square foot the roof load is equal to 70 of the product of the exposure thermal and importance factors the ground snow load and 20 pounds. One of them is that flat roofs leak more easily than pitched ones. From our example our ground load and flat roof snow load were found to be 30 psf and 21 psf respectively. When discussing snow load with anyone it is crucial to have a clear understanding as to if the load is a ground or flat roof snow load.

Other considerations for sloped roofs can be found throughout chapter 7 of asce 7 10. There are a few common misconceptions regarding flat roofs that are stubbornly persistent. This is all of the natural stresses imposed upon a roof such as snow loads rain loads and wind loads. Provisions on how to calculate the snow drift surcharge for structures can be found in section 7 8 of asce 7 10.

Determine the transient load of the roof. This is highly regional as weights of snow for example range from 10 to 300 pounds per square foot based on moisture and volume of the snow. As a result equation 7 1 which accounts for loss between events will result in a non conservative value. If you have any concerns as you are determining your flat roof snow load consult with a structural engineer or roofing specialist.

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. Express the result in feet rather than inches. Asce 7 05 equation 7 1 assumes that the snow load results from multiple events. For example 18 inches would be 1 5 feet.