Hail testing: natural slate confirmed to be impact resistant

October 23, 2016

Have you always wondered how natural slate holds up to hail? Recently, under the guidance of the National Slate Association, testing was done and it was confirmed that natural roofing slate can withstand damage from hailstone impact.

This testing was conducted on North American produced S-1 rated natural roofing slate by Architectural Testing of Southlake, Texas, in accordance with Factory Mutual FM 4473, Specification Test Standard for Impact Resistance Testing of Rigid Materials by Impacting with Freezer Ice Balls

Slate shingles that were 3/8” and 1/4” thickness were tested. In order to pass the test, the slate shingles had to survive two direct hits at the same target point by ice balls fired from a compressed air launcher at two different target locations on the slate.

The 3/8” thick slate met Class 4 requirements, surviving the impact of 2” ice balls traveling at 76 MPH. The 1/4” thick slate met Class 3 requirements, surviving the impact of 1 3/4″ ice balls traveling at 69 MPH.

roof slate with hail and snow

For questions related to these test reports, please contact the National Slate Association toll free at 866-256-2111 or email