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Snow Loading - Aluminum Patio Covers and Carports

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It is our contention that all homeowners should be aware that heavy snow accumulations in your area could pose a potential problem with overloading of roofs. In particular, flat roofs with changes in elevation are vulnerable to snow drifting and thus heavier loading. Also, it is well known that snow that accumulates and remains on a roof over a prolonged period of time tends to both compact and change into a heavier crystalline form. With the accumulation of additional snow, overloading and even failure of the supporting roof structure is possible.

All building roof structures are designed to a Roof Snow Load (RSL) as prescribed by the governing Building Code (which is a municipal designation) and are a function of the Ground Snow Load (GSL). For example:

• The ground snow load within a municipality is 22 psf.
• The ground snow load within a municipality is 42 psf.
• The ground snow load within a municipality is 40 psf.

psf. = pounds per square foot

Freshly fallen snow weighs from 5 to 12 lbs. per cu. ft.; compacted or wet snow weighs from 15 to 50 lbs. per cu. ft. Thus the above GSL would be exceeded with accumulations of snow having an average density of say 20 pcf when depths exceed 13 in., 25 in. and 24 in. respectively for Detroit or Windsor.

Responsible parties should ensure that roofs are continually monitored during periods of heavy snow accumulations and repeated snow falls. Remember that greater snow accumulations may occur from one storm than from another due to changes in wind velocity and direction.

Additional notes:

GENERALLY - to be uses as a guideline only...

• A 20 psf. rating is roughly equal to a roof being able to sustain 3" of standing water.
• A 20 psf. rating would be able to sustain 30-40 mph winds.
• A 30 psf. rating would be able to sustain 90 mph winds.
• A 40 psf. rating would be able to sustain 110 mph winds.

A light fluffy snowfall will weigh an average of 8 pounds per cubic foot. In order to get up to a 20 psf. snow load rating you could allow 2.5 feet of fluffy snow to fall.

A wet snow fall will weigh an average of 32 pounds per cubic foot. In order to get up to a 20 psf. snow load rating you could allow 8" of wet snow to fall