Ground snow load in Illinois

These are the stations with the highest 50-year ground snow load estimates in the state. Each value is a statistical estimate derived from that station’s snow record, not a measured load, and not a design value for any particular address.

Even across Illinois’s comparatively modest 710 ft elevation spread, estimated values vary from 7 to 36 psf. Local snow climate matters more than any single statewide figure.

A 50-year ground snow load is the weight of snow on the ground, in pounds per square foot, with a 2% chance of being exceeded in any given year. It is the statistical basis of the ground snow load maps in ASCE 7-16 and earlier building codes, and the form of value their site-specific case studies call for. (ASCE 7-22 moved to strength-level values on a different basis; see what changed in ASCE 7-22.)

The values above are per-station estimates from SR-20-1, the ERDC/CRREL report federal agencies use for site-specific snow load analysis. Each is derived from the snow measurements at that station, so it describes the station’s location, not your address. Between stations, the defensible way to estimate a value is the SR-20-1 case-study method: take the surrounding stations, adjust for elevation, and interpolate.

If you own a building, your design snow load is set by your local building department; the guide on how much snow a roof can hold explains what the number means for an existing roof.

If you are designing one somewhere the map is coarse or marked for a case study, Nivometra runs the SR-20-1 methodology for an exact location: it selects the relevant surrounding stations, shows you every one on the map with its elevation and record, and documents the interpolation in a report you can hand to a reviewer.