Snow Load on Roofs by ZIP Code
The estimated weight of the snow on the ground and on a typical roof where you live, from NOAA's daily snow model, plus a calculator for any depth of snow.
Look up a ZIP code
Daily estimates run from October through May and start with the first nightly update.
Snow load calculator
How much the snow on a roof weighs, from its depth and the kind of snow. The answer is the weight per square foot; add your roof's area for the total.
About 6 lb/sq ft
12″ of average new snow holds about 1.2″ of water, and each inch of water weighs 5.2 lb per square foot.
| Kind of snow | Typical water share | 1 foot of it weighs about |
|---|---|---|
| Light, fluffy new snow | 7% | 4 lb/sq ft |
| Average new snow (10 to 1) | 10% | 6 lb/sq ft |
| Wet, heavy new snow | 20% | 12 lb/sq ft |
| Settled or packed older snow | 30% | 19 lb/sq ft |
| Ice | 92% | 57 lb/sq ft |
Typical values only. New snow ranges from under 5% water (dry powder in the cold Rockies) to over 20% (wet snow near the coast), and a snowpack gets denser as it settles. The ZIP lookup above uses NOAA's modeled water content for your area instead. Source: National Storms (nationalstorms.com), CC BY 4.0, data from NOAA NOHRSC SNODAS (ZIP estimates) and standard water weights (calculator).
What these numbers mean for a roof
Why the roof number is lower than the ground number. Wind and heat from the house usually leave less snow on a roof than on the ground. Building codes start from about 70% of the ground load for a flat, heated roof in the open, so we show a typical roof as 70% to 100% of the ground weight. That is a typical case, not your roof: snow drifts against walls and taller roofs, slides into valleys and onto lower roofs, and piles up where it's shoveled or falls off a higher roof. Those spots can carry two or three times as much. Rain falling on snow adds weight without adding depth.
This is an estimate of the snow, not an inspection of any roof. Whether a roof can carry it depends on its design snow load, its age and condition, and how the snow has drifted. Your local building department can tell you the design snow load for your address, and a licensed structural engineer or roofing contractor can look at the roof itself. You'll often find the design snow load on the house plans or the building permit. If you see sagging, new cracks in walls or ceilings, doors that suddenly stick, or hear creaking, get off the roof and call a professional. Don't climb onto a snowy roof to clear it yourself; a roof rake from the ground or a contractor is the safer way.
How we estimate
Every morning from October through May we read NOAA's SNODAS snow model (the Snow Data Assimilation System, run by the National Operational Hydrologic Remote Sensing Center). It estimates the depth of the snow and how much water it holds for every square kilometer of the lower 48 states, as of 06:00 UTC (1 a.m. EST), blending weather models with satellite, airborne and ground observations. We take the value at the Census center point of each of about 33,000 ZIP codes and 6,900 cities and turn the water into weight: 1 inch of water weighs 5.2 lb per square foot, whatever the depth of the snow it's in. A 1-km cell is an average: the snow in your yard can be deeper or shallower, especially in the mountains, near lakes and where snow drifts.
More winter pages: snowfall totals by ZIP code · snowiest US cities this winter · wind chill calculator
Sources
Snow water equivalent and snow depth: National Operational Hydrologic Remote Sensing Center (NOAA), Snow Data Assimilation System (SNODAS) Data Products at NSIDC, Version 1 (dataset G02158, National Snow and Ice Data Center, doi:10.7265/N5TB14TC); background on the NOHRSC National Snow Analyses. ZIP code points: US Census Bureau ZIP Code Tabulation Areas (2024 Gazetteer). Weight of water: 62.4 lb per cubic foot. This page is not affiliated with NOAA, NSIDC or the National Weather Service.