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Ground-to-Roof Snow Load Calculator

Convert ground snow load to flat-roof design snow load per ASCE 7.

Computed in your browser — nothing you enter is uploaded. Figures are presented in United States units and terminology, and each formula’s basis is cited under regulatory standards below.

Last verified 2026-08-26 · v1.0.0

Market
Imperial · sales tax

Flat-roof design snow load

0.1523 psi

High confidence

With the figures above, the flat-roof design snow load comes to 0.15 psi. This is presented for United States. Building in another market? Change the selector above and the units and terminology follow.

Add the equipment this sizes

This result is a specification — 0.1523 psi — not a quantity. Put the thing it sizes into your project: how many, what you call it, and your supplier’s price.

Preliminary estimate, not certified engineering. This tool produces an indicative quantity calculation for planning purposes only — it is not a certified structural analysis, a guaranteed material takeoff, or a substitute for building department approval. Always verify measurements on-site and have a licensed contractor or structural engineer review any load-bearing, code-sensitive, or safety-critical work before purchasing materials or starting construction. Spotted an arithmetic or standards error? Report it to contact@craftquantities.com with your inputs — a confirmed fix gets a permanent check of its own, so the same mistake cannot come back.

Presented in US customary units and US trade terminology. Where a formula follows a published standard, that standard and its edition are cited beside it on this page; where none governs, the page says so. Local amendments override model codes — verify against the code in force where you build.

Regulatory standards & verification citations

  • ASCE 7 flat-roof snow load: pf = 0.7 × Ce × Ct × Is × pg, where Ce is exposure factor, Ct is thermal factor, Is is importance factor, and pg is ground snow load

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Frequently asked questions

What do Ce, Ct, and Is represent?
Ce is the exposure factor (wind exposure and terrain, which affects snow drifting off the roof), Ct is the thermal factor (heat loss through the roof that melts snow), and Is is the importance factor (based on the building's risk category) — all per ASCE 7.
Why does the formula start with a 0.7 factor?
ASCE 7 applies a 0.7 base factor to the ground snow load as a general reduction, reflecting that flat roofs typically retain somewhat less snow than open ground, before the exposure, thermal, and importance factors are layered on.
Is this the final design snow load for my roof?
This calculates the base flat-roof snow load (pf) only — sloped-roof reduction factors, unbalanced or drift loading, and rain-on-snow surcharge (also part of ASCE 7) are separate checks not included here.