Metal Roof & Steel Building Snow Load Guide

Metal roofs and steel buildings are everywhere in snow country because they shed snow well. ASCE 7 recognises that by classifying smooth metal as an unobstructed slippery surface, which changes the slope factor.

Slippery means it sheds sooner

On a warm roof, a slippery surface's slope factor Cs starts reducing the load at just 5°, versus 30° for shingles. So a metal roof at a moderate pitch carries noticeably less balanced snow than an equivalent asphalt roof.

Don't forget the thermal factor

Many steel buildings are unheated, so they use Ct = 1.2 rather than 1.0, which adds load and partly offsets the slippery benefit. Enter the real thermal condition, not an optimistic one.

Sliding snow is the catch

A slippery roof dumps its snow somewhere. ASCE 7 §7.9 sliding-snow loads land on lower roofs, walkways and equipment below. Plan where the snow goes and keep entrances and lower roofs clear of the slide path.