Ground snow load in Iowa

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 Iowa’s comparatively modest 1,020 ft elevation spread, estimated values vary from 11 to 62 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.