You need to use a snow load formula for flat roofs.
Flat roof for snow load.
Minimum flat roof snow load values.
From our example our ground load and flat roof snow load were found to be 30 psf and 21 psf respectively.
Provisions on how to calculate the snow drift surcharge for structures can be found in section 7 8 of asce 7 10.
In our case let s assume that our structure has a flat roof roof slope 5.
In regions with relatively low snow load values the load from a single event may result in the peak loading.
Determine the transient load of the roof.
Online snow load calculator for buildings with flat or low slope roofs for balanced snow drift and rain on snow surcharge loadings calculator asce 7 05 for structural engineers construction professionals and building planners.
Express the result in feet rather than inches.
First figure out how deep the snow is piled up there.
The snow load that is applied to our structure is not the ground snow load but in most cases the flat roof snow load.
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.
If you have any concerns as you are determining your flat roof snow load consult with a structural engineer or roofing specialist.
Another is that they cannot handle as much snow weight as pitched roofs because the snow sits directly on the roof.
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.
This is all of the natural stresses imposed upon a roof such as snow loads rain loads and wind loads.
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.
Asce 7 05 equation 7 1 assumes that the snow load results from multiple events.
One of them is that flat roofs leak more easily than pitched ones.
The flat roof snow load is calculated using formula 7 3 1.
For example 18 inches would be 1 5 feet.
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.
As a result equation 7 1 which accounts for loss between events will result in a non conservative value.
