(a) Quality. Asbestos-cement shingles shall have a dense, hard structure and be well seasoned and listed as not less than Class B roof covering material by Underwriters Laboratories, Inc.
(b) Underlay. The roof sheathing shall be covered with an underlayer of asphalt-saturated asbestos or rag felt weighing not less than fourteen pounds per square.
(c) American Method. Individual standard shingles shall weigh not less than 470 pounds per square and strip shingles shall weigh not less than 250 pounds per square. The maximum exposure to the weather shall be seven inches for the sixteen inch length, six and one-half inches for the fifteen inch length and five inches for the twelve inch length.
(d) Dutch Method. The minimum weight shall be 265 pounds per square. When applied the minimum head lap shall be three inches and the minimum side lap shall be four inches.
(e) French or Hexagonal Method. The minimum weight shall be 250 pounds per square. There shall be overlaps on at least two edges for a distance of not less than three inches.