How much does the snow on my roof weigh?

The weight of snow per square metre equals its depth, in metres, multiplied by its density. The commentary on snow loads of the National Building Code, reproduced in an appendix of the British Columbia Building Code, uses about 100 kg/m³ as the average for fresh snow in Canada. It gives 2 to 5 kN/m³ for old snow, or about 200 to 510 kg/m³.

A digest from the National Research Council of Canada notes that snow density rises to about 0.2 after a few days and to about 0.3 after a month, or 200 and 300 kg/m³. The 500 kg/m³ value matches the top of the old snow range. The Régie du bâtiment du Québec (RBQ, Quebec's building authority) points out that thaws and rain make snow denser, and so heavier.

The calculated weight does not tell you whether your roof will hold. The load each roof must carry is set when it is designed, and the RBQ refers this question to a structural engineer. No official source consulted gives a depth at which to clear a roof. The RBQ recommends having the roof cleared as soon as signs of overload appear, whatever the amount of snow.

Cracks in interior walls, doors that stick, unusual creaking, a ceiling that sags: leave the building with everyone and call 911.

Condominium manager, broker, inspector or neighbourhood association: you can link to this calculator from your website. It is free.

<a href="https://toiture-laval.com/outils/poids-neige-toit-laval/en/">Snow weight on a roof calculator</a>