Roofing slates are split by hand with hammer and chisel to reveal a natural cleft surface. Splitters are very good at their trade but the thickness varies slightly and slates are grouped into different classes. This variation reinforces the fact that slates are a natural stone product not a uniformly consistent synthetic material. While some quarries may split and sort to slightly different thickness groupings, most roofing slate is grouped into the following thickness categories:
3/16" to 1/4"
Historically known as "commercial thickness", but currently limited in production. Estimated weight is 800 pounds per square.
1/4" to 3/8"
Also known as "nominal quarter inch" and it is the current industry standard thickness in North America. Slates in this category are split for a target of ¼", thus some slightly thinner slates may be included. This is not intended to be a blend of ¼" and 3/8" thick slates. If full 3/8" thick slates are desired, 3/8-1/2" slates should be ordered. Estimated weight is 1000 pounds per square, but most range from 875 to 950.
3/8" to 1/2"
A form of "heavy slate" or "heavies", this thickness range and thicker is generally made from coarse stone, which typically yields a greater amount of texture. Estimated weight of 1300 to 1500 pounds per square.
1/2" to 3/4"
Custom produced heavies. Estimated weight is 1800-2000 pounds per square. Some quarries may break this category down into ½-5/8" and 5/8-3/4", in which case the 5/8-3/4 may weigh as much as 2500 pounds per square.
3/4 to 1"
Custom produced heavies. Estimated weight of 3000 pounds per square. Slates that are 20" in length or longer AND ¾" or thicker should be specified to have 4 nail holes per piece
1" to 1 1/4"
Custom produced, roughly 4000 pounds per square.
1 1/4" +
Custom produced, roughly 5000+ pounds per square.
Please note that:
363 VT Rt. 30 S