Slate Hail and Fire Test

Natural Slate Hail Testing

Impact Resistance of Natural Slate Confirmed

Under the guidance of the National Slate Association, laboratory testing was recently conducted to confirm the ability of natural roofing slate to withstand damage from hailstone impact.

Natural Slate Hail Testing Results
The 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 at 3/8” and 1/4” thickness was tested. The slate shingles must 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.

• Complete details of the Hailstone Test Report

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

The cannon
Taking aim
The impact
Close-up of impact

Fire Resistance of Natural Slate Roofing

IBC Class A Fire Resistance Rating Received

The National Slate Association (NSA) and National Roofing Contractors Association (NRCA) recently teamed-up to conduct testing of the fire resistance of a slate roofing system in accordance with UL 790, “Standard Test Methods for Fire Tests of Roof Coverings.”

Fire Resistance of Natural Slate Roofing
The testing was inspired by a change in the International Building Code (IBC), the 2009 edition of which recognizes slate roof assemblies as having a Class A fire resistance only when installed over a noncombustible roof deck. Previous editions of the IBC designated slate roof coverings as having a Class A rating when installed over combustible and noncombustible roof decks. The test assembly consisted of nominal 1/4-inch thick, North American slate shingles laid with a 3-inch headlap over No. 30 felt underlayment on a 1/2-inch plywood roof deck. The tested assembly achieved a Class A rating.

While it is hoped the favorable test results can be used to substantiate the fire resistance of similarly constructed slate roof assemblies, NSA and NRCA will continue to work together to exempt slate roof coverings from testing to determine their fire classification in future editions of the IBC.

• Complete details of the Slate Fire Resistance Test Report

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

Setting up the burning brand test deck.
Burning brand test in progress.
After the burning brand test.
Close-up of the bottom of test deck after the burning brand test.

These photos are posted with permission from Mark_S_Graham, see additional photos on Flickr.

QR code

National Slate Association’s Mobile Field Guide is available free of charge via an internet browser on your smart-phone* or tablet when an internet connection is available.Or you may also scan the QR code here with your QR reader.

Click here to download the Mobile Field Guide press release.

*The NSA Mobile Field Guide is best viewed on iPhones, iPads and the newer Android phones. Windows® smart phones are not supported at this time. The mobile site is not intended or formatted for desktop computers or laptops.