Rain-on-Snow Surcharge (ASCE 7-22 7.10)

The rain-on-snow surcharge added to the balanced flat-roof snow load where the ground snow Pg is 20 psf or less and the roof slope (deg) is less than W/50 (W the eave-to-ridge distance). ASCE 7-22 raised this to 5-8 psf (commonly 8) from the older flat 5, because a low-slope roof in wet-snow climates holds rain a steeper roof would shed. A Pf of 15 psf at Pg 18 low-slope becomes 23 psf; a deep-snow region (Pg 25) takes no surcharge, staying 15 psf. Balanced case only, both triggers required. A design aid, not a substitute for the engineer of record.

applies = (pg <= 20 psf) AND (slope_deg < W/50); total = pf + (applies ? surcharge : 0); ASCE 7-22 surcharge 5-8 psf (default 8).

The ASCE 7-22 §7.10 rain-on-snow surcharge load, by name.

ASCE 7 is available through the ASCE Library at ascelibrary.org; the §7.10 trigger and surcharge are public.

Estimate. AHJ and licensed professional govern.

Field names used by the API: pf_psf, pg_psf, slope_deg, eave_to_ridge_ft, surcharge_psf, total_psf

• Trigger Pg <= 20 psf and slope (deg) < W/50ASCE 7-22 §7.10
• Surcharge 5-8 psf (default 8) added to the balanced Pf onlyASCE 7-22 §7.10
• Balanced only not added to drift, sliding, or partial-load casesASCE 7-22 Ch. 7