Roof Snow Drift

The two directions of wind that cause snow drifts are windward and leeward.

Roof snow drift.

So about 4 feet of fresh snow would have to be on your roof for it to become stressed. An example of a long drift which formed in a step on a very large roof 250m 800ft is shown in the photograph on page 1. Experience with ground level drifting patterns indicates that with a very large source of snow drift ratios could reach 6 1 or 7 1. 10 12 inches of new snow equates to 5 lb per square foot of roof space.

Windward drift results from snow blown against a projection or wall below a high roof. For more information visit. The maximum drift load is. In most situations varying.

Windward snow drifts occur when wind blows snow from a lower elevation roof towards the wall of an adjacent higher roof. Leeward snow drifts occur when wind blows snow off of a higher elevation roof down onto an adjacent lower roof. Density snow density γ. This shows the effects of snow drift on the roof of a building.

Version 0 0 3 december 29 2020. To understand just how much stress snow can put on your roof check out the following ibhs snow roof guidelines. Only 3 5 inches of old snow is needed to reach that 5 lb of per square foot of roof space so over 2 feet of packed snow may be too much stress for your roof. The drift load shall be added to normal roof snow load.

Snow drift length height of triangle. Packed snow is a little different. Importance factor i s. Rain load s r.

Snow drift load is in a triangular shape with maxim load pd at edge between upper and lower roof and decrease to zero for a length w. Ground snow load s s. Of the drift would have a 3 1 or 4 1 length to height ratio. Typically the windward drift height hdw is less than the leeward drift height hdl unless the length of the lower roof is considerably longer than the length of the upper roof.