01
Start with the stone
Ward connects slate’s long service potential with material testing. ASTM C406/C406M classifies roofing slate using breaking load, water absorption and depth of softening, measured through C120, C121 and C217 respectively. These properties help assess the stone; they do not establish a hurricane rating for every roof made from it.
02
Read storm tests as assembly results
A 2008 technical article by Matthew Hicks reports a slate roof assembly tested at a 2:12 slope with simulated rain of 8.8 inches per hour and winds reaching 110 mph. The table records no slate movement or water infiltration beneath the deck. These results apply to that test assembly, not all slate products or installation methods. The report does not substantiate the additional 140-mph gust claim. A test slope is also not an installation approval: Greenstone’s Miami-Dade NOA 22-0419.12 specifies 3½:12 or greater, plus detailed deck, underlayment and fastening requirements. Check the applicable product approval and project requirements.
03
Separate longevity from a warranty
S1 slate is associated with an expected service life exceeding 75 years, dependent on location and exposure. That is different from a contractual warranty. Coverage and exclusions vary by supplier; North Country Slate, for example, offers a limited 75-year material warranty excluding removal and installation labor. Long service and repairability are useful sustainability considerations, but neither establishes that slate outperforms every competing roof system. Material selection, complete roof design, skilled installation and maintenance all deserve attention.