Porosity is one part of performance
Fired clay can absorb water through its pore structure. The amount and behavior depend on the product, so color, apparent density or age alone cannot establish suitability for an exposure. Historic clay tile may remain serviceable while isolated units deteriorate. Evaluate the tile and the conditions affecting it rather than treating every weathered surface as proof that the whole roof has failed.
Ask for the relevant evidence
Obtain the manufacturer’s stated compliance, testing information and intended use for the exact product. ASTM C1167 addresses clay roof tiles, but a reference to a standard is not a substitute for the product documentation or for reading the applicable edition. Avoid transferring an absorption number or exposure classification from a different tile into the project specifications.
Look beyond the tile body
Persistent wetting can involve drainage, debris, flashing, damaged overlaps or condensation. A roofer or preservation professional should record where deterioration occurs and compare exposed, sheltered and repaired areas. That pattern may be more informative than one broken sample. Have any proposed replacement evaluated for both material suitability and physical compatibility with the retained roof.
Further reading & technical sources
- National Park Service · Preservation Brief 30 ↗
- ASTM · C1167-22, Standard Specification for Clay Roof Tiles ↗
- Building America Solution Center · Clay or Concrete Tile Roofs ↗
Consult the current product documentation and local requirements for your project. These introductions are not installation specifications.
More tile roofing guides
- How to read a clay tile data sheet
- What ASTM C1167 does—and does not—tell you
- A clay roof tile submittal checklist
Tile Roofing USA editorial guide · Published October 28, 2026.