Roof Snow Load Vs Ground Snow Load

Consequently the roof design snow load is taken to be less than the ground snow load.

Roof snow load vs ground snow load.

Roof snow load is a much more important statistic and is computed from the ground load in a region. Length of high roof lu. Ground snow load refers to the weight of water per square foot that is exerted on the ground by the snow pack. Length of low roof ll.

In other words on a steep roof less material would be stacked in a concentrated area at one time to avoid having it slide off. Length of roof upwind of the snow drift. The value used for the ground snow load should represent the snow load that has a 50 year mean recurrence interval or in other words a 2 probability of being exceeded in any given year. Figure 7 1 pages 84 85 and table 7 1 page 92.

This statistic is not often directly relevant although heavy snow can damage some landscaping features. In our case let s assume that our structure has a flat roof roof slope 5. The basis for the snow load computation in asce 7 05 is the ground snow load. 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.

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. The equation for converting ground snow load p g to roof snow load p f is asce 7 05 equation 7 1. The snow load that is applied to our structure is not the ground snow load but in most cases the flat roof snow load. The truss could be designed based on the assumption that the 25 psf roof snow load is a factored ground snow load in which case a ground snow load is back calculated using asce 7 based on the specified roof snow load pg 25 psf therein lies the problem with specifying only a roof snow load.

Paolo formichi university of pisa italy. Ground snow load pg. Length of roof downwind of the snow drift. In my region on cape cod we have a ground snow load design of 25 psf which is a greater design load than the live load 12 psf to 20 psf over an entire roof system.

Background and applications section 4 snow load on the ground the snow load on the roof is derived from the snow load on the ground multiplying by appropriate conversion factors shape thermal and exposure coefficients. From eave to ridge w. Horizontal distance from eave to ridge. This equation includes factors that take into account exposure and building heat loss.

Pf is flat roof snow load if as a consumer your concern is snowfall and you want to upgrade the ability of your building to carry it this is the value to increase.