How to Estimate Your Roof's Current Snow Weight

You don't need a scale to estimate how much snow your roof is carrying. Two measurements and a density lookup give you a reasonable psf number you can compare to the design load.

Measure snow depth

Measure snow depth on a flat, open surface near your home; a deck table or garden table works well as a snow board. This proxies what is on the roof; the actual roof depth may differ if the roof is warmer (melts from below) or if wind has redistributed snow.

Estimate density by snow type

Fresh powder: 3–5 pcf. Light settled snow (1–3 days old): 6–9 pcf. Dense older snow (4+ days, warmed): 10–15 pcf. Wet, heavy snow (near freezing, compacted): 18–25 pcf. Use 12 pcf as a general middle-ground for mixed snow from a typical storm.

Calculate the load

Load (psf) = depth (feet) × density (pcf). Example: 18 inches (1.5 ft) of dense snow at 15 pcf = 22.5 psf. At 25 pcf (very wet) it is 37.5 psf, well into the danger zone for roofs designed for lighter loads.

Compare to your design load

The design roof snow load for your location from ASCE 7 (which you can calculate here) is the code limit. If your estimate approaches that number, consider snow removal. If it already exceeds it, remove snow immediately and watch for structural warning signs.

Account for layering

After multiple storms without melting between them, the roof may carry several distinct layers with different densities. Estimate each layer separately and add them. A week of repeated storms can accumulate 3–4 layers, and the base may have been compacted to 20+ pcf while the top is fresh powder.