01
Calculate the installed assembly
The slate itself is only part of the total roof. Structural review may also include the deck, underlayment, flashings, snow-retention equipment and other permanent components. Project location adds code-prescribed snow, wind and maintenance loads that are separate from the slate weight.
02
Thickness and coverage drive quantity
Thicker stone generally weighs more per unit area, while exposure determines how many courses and pieces cover the roof. Small slates or reduced exposure can increase the number of pieces and overlaps. Use product-specific data and the actual layout rather than a rule-of-thumb alone.
03
Existing buildings need evidence
For reroofing, an experienced professional should examine framing, spans, connections, deck condition and previous alterations. Removing a light roof covering does not automatically prove the structure is ready for conventional slate. Lightweight real-slate systems may reduce load, but they still require a complete project review.