The rules of thumb used
Snow weight varies with density, so public-safety guidance often uses approximations: roughly 10–12 inches of fresh snow, 3–5 inches of old packed snow, or about 1 inch of ice each weigh around 5 pounds per square foot. This estimator uses 0.5 psf per inch of fresh snow, 1.25 psf per inch of packed or wet snow and 5 psf per inch of ice.
| Layer | Approximate weight |
|---|---|
| Fresh, dry snow | ~0.5 lb per sq ft per inch |
| Packed or rain-soaked snow | ~1.25 lb per sq ft per inch |
| Ice | ~5 lb per sq ft per inch |
Why the reference capacity is only a placeholder
Real capacity depends on framing, span, age, condition, drifting and the code in force when the building was built. The 30 psf default is illustrative. Flat and low-slope commercial roofs, drifts beside parapets and older barns deserve a professional look. Never climb onto a loaded roof; snow removal is a job for insured professionals.
When snow becomes a claim
Sagging ceilings, doors that suddenly stick, cracking sounds and new leaks can signal stress. If damage occurs, photograph it, mitigate safely and see ice dam and snow load claim appraisal for how collapse and ice dam losses are valued.
About this estimator
Is this an engineering assessment?
No. It’s a rough estimate based on public rules of thumb. Only a qualified engineer can assess a roof’s capacity.
Why does rain on snow matter so much?
Snow acts like a sponge. Rain adds weight without melting much of the pack, which is why loads spike after a rain-on-snow event.
Does insurance cover roof collapse from snow?
Many policies cover collapse caused by the weight of ice or snow, subject to the policy’s terms. Check your collapse wording.