Find Your Roof Snow Load by ZIP Code

Your ZIP code is the starting point for finding your snow load, but the calculation does not end there. Here's the full path from ZIP code to design roof load.

Step 1: Ground snow load for your location

The ground snow load Pg is the weight of snow that accumulates at a site, in psf. It is set by ASCE 7 and varies by location: not just by ZIP code, but by precise latitude/longitude and sometimes elevation within a ZIP code. The authoritative source is the ASCE 7 Hazard Tool, which accepts a lat/lon or address. Your local building department also publishes a jurisdiction-adopted value, which may differ slightly from the ASCE map.

Step 2: Convert to a roof snow load

The roof does not carry as much as the ground, because wind and a little heat remove some snow. ASCE 7 Equation 7.3-1 converts ground snow load to flat-roof snow load: Pf = 0.7 × Ce × Ct × Is × Pg. The factors (exposure, thermal and importance) depend on your specific roof and building type, not just location.

Using RoofHelm

Enter your ground snow load (from your building department or the ASCE 7 Hazard Tool for your address), then select your exposure condition, thermal category and risk category. The calculator applies the equation and shows the flat-roof load, slope reduction and, if you enter a step or drift geometry, the drift surcharge.

Why it can't be one-click by ZIP

A single ZIP code can span multiple elevations, terrain exposures and roof types. Two houses on the same street with different pitch, thermal conditions and surroundings will have different design loads. The ZIP code gives you Pg; the full calculation gives you the number that governs your roof.