StacksVerified U.S. regulatory reference

30 CFR §57.22221

Verified against eCFR.gov as of June 20, 2026View official text on eCFR.gov ↗
Overcasts and undercasts shall be—
  1. (a)Of substantial construction;
  2. (b)
    1. (1)Constructed of noncombustible materials; or
    2. (2)Where constructed of combustible materials, the outside surfaces shall be coated with at least one inch of construction plaster containing perlite and gypsum; at least one inch of expanded vermiculite, Portland cement and limestone; or other coatings with equivalent fire resistance;
  3. (c)Kept clear of obstructions.