01
What the classification addresses
ASTM C406 classifies roofing slate using referenced test properties associated with expected service. S1 is the highest service classification within that framework. The report should be current, product-specific and tied to representative material from the named source.
02
What S1 does not guarantee
A classification does not design the roof, verify every delivered piece or correct poor storage and installation. Thickness, size, sorting, fastening, flashings, exposure, headlap and climate remain part of performance. Documentation should be reviewed in the context of the project specification.
03
Ask for traceable documentation
The supplier should be able to identify the slate and provide relevant reports. Check laboratory, sampling date, product name and reported results. When the source or product changes, old paperwork from unrelated material should not be treated as proof.