Roof - Weight of Snow

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Equation / Last modified by KurtHeckman on 2018/06/01 13:02
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The Weight of Snow on a Roof calculator estimatesRoofCOVERAGE-illustration.png                        Roof dimensions  the weight of snow on a roof based on the roofs dimensions and the type and depth of snow.

INSTRUCTIONS: Choose units and enter the following:

  • (l) The length of your roof
  • (w) The width of your roof
  • (p) The pitch of your roof
  • (d) The depth of the snow on your roof.

Weight of Snow (SW): The Weight of Snow on a Roof is returned in pounds.  However, this can be automatically converted to other weight and mass units (e.g. kilograms or tons) via the pull-down menu.

Water, Rain and Snow Calculators:

Type of snow or ice(kg/m3)
Fresh New snow 50-70
Damp new snow100-200
Settled snow200-300
Depth hoar100-300
Wind packed snow350-400
Firn   (granular)400-830
Very wet 700-800
Glacier ice830-917

The Math

The dimensions of your roof are used to compute the roof's surface area.  That area is based on the length and width of the area covered and the pitch.
The formula works for gabled roofs (two sided) and single sided roofs (see diagram).  For gabled roofs, this formula is only accurate if the both gables have the same pitch, which puts the ridge in the middle. For roofs with different pitches, calculate each side separately.  

The depth of the snow combines with the surface area to compute the volume of snow.  With that, and the type of snow, one can reasonably estimate the weight of snow on one's roof.

Ignoring minute traces of other substances, snow is frozen water.  This equation uses a median value for the Snow Water Equivalent (SWE) based on the type of snow or ice selected:

To reduce the weight of snow on one's roof, many people use a roof rake to pull large quantities of snow off of the roof.