Clay & Slate Roofing Inspection

Clay tiles weigh 9–12 lbs/sq ft; slate weighs 7–10 lbs/sq ft — significantly heavier than asphalt shingles (2–4 lbs/sq ft). Per IRC R301, the roof structure must be engineered to support the dead load of tile/slate plus live loads (snow, maintenance). A structural engineer assessment is required when re-roofing from lighter material to tile/slate.

1. Verify structural engineer has assessed roof framing capacity for tile/slate weight

2. Check rafter/truss sizing matches engineering specifications

3. Confirm sheathing type and thickness is adequate (minimum 5/8" plywood for tile)

4. Verify any required reinforcement (sister rafters, added purlins) has been installed

5. Check load path is continuous to foundation

6. Assess snow load requirements — tile + snow may exceed original design load

- Roof structure not assessed — sagging, cracking, or collapse under tile weight

- Re-roofing from shingles to tile without structural upgrade — overloaded framing

- Purlins/battens not properly sized or spaced — tiles sag between supports

Per IRC R905.3 and R905.4, two layers of underlayment are required for tile and slate roofs (or approved synthetic equivalent). Ice and water shield at eaves in cold climates (same requirements as shingles). Tile roofs often use battens over underlayment for drainage plane. High-temp underlayment recommended under dark tiles (heat can degrade standard felt).

1. Verify double layer of underlayment or approved single-ply synthetic

2. Check ice and water shield at eaves, valleys, and penetrations

3. Confirm high-temperature underlayment used under dark tiles (rated to 240°F+)

4. Verify battens installed over underlayment (if required by tile system)

5. Check counter-battens for drainage plane in steep or complex roofs

6. Confirm all overlaps meet code minimums (19" for double-coverage felt)

- Standard felt under dark tiles — heat degrades felt in one season

- Single layer of underlayment — code requires double layer for tile/slate

- No drainage plane (counter-battens) — trapped moisture rots deck

Per manufacturer specifications, battens must be spaced to match tile exposure (varies by profile — typically 13–14" for standard S-tile, 10" for flat tile). Battens must be pressure-treated or rot-resistant wood, minimum 1"×2" (2"×2" for slate). Layout must account for field tiles, hip/ridge tiles, and cut tiles at valleys and rakes.

1. Verify batten spacing matches manufacturer's specified exposure for the tile profile

2. Check batten material — pressure-treated or naturally rot-resistant wood

3. Confirm battens are properly fastened to rafters (through sheathing, not just to sheathing)

4. Verify layout is planned for full tiles at visible areas (cuts hidden at hips/valleys)

5. Check eave closure/bird stop installed at first batten

6. Verify ridge batten position allows proper ridge tile seating

- Inconsistent batten spacing — tiles don't align, water channels form

- Battens rot (untreated wood) — tiles loosen and slide

- No bird stop at eave — birds and pests nest under tiles

Per IRC R905.3/4 and manufacturer specs, all tiles must be mechanically fastened (nails or screws) — not just gravity-set. In high-wind zones (>110 mph), every tile must be fastened. Fasteners must be corrosion-resistant (stainless steel or hot-dipped galvanized). Slate requires two copper or stainless nails per piece. No tile should bear weight on the tile below.

1. Verify all tiles are mechanically fastened per manufacturer and code requirements

2. Check fastener type — corrosion-resistant (copper nails for slate, stainless for clay)

3. Confirm each tile hangs on the batten, not resting on the tile below (no weight stacking)

4. Verify consistent exposure and alignment across the roof surface

5. Check for cracked or broken tiles — tap test for slate (dull sound = cracked)

6. Verify hip and ridge tiles are properly mortared or mechanically fastened

7. Check that tiles at rakes and valleys are properly cut and sealed

- Tiles not fastened — wind lifts and removes tiles (especially in hurricanes)

- Weight-stacking — lower tiles crack under accumulated weight

- Wrong fastener material — galvanized nails in coastal areas corrode rapidly

- Cracked slate installed — develops leak within first year

Per IRC R905.3/4, flashing for tile/slate roofs requires heavier gauge metal than shingle roofs (minimum 26-gauge galvanized or 16-oz copper). Valley flashing must be wider (minimum 24" W-valley). Step flashing at walls must integrate with tile profile. All penetrations require custom-fitted lead or copper flashings shaped to match tile contour.

1. Verify valley flashing is proper width and gauge for tile weight

2. Check step flashing at walls — must work with tile profile, not just flat

3. Inspect chimney flashing: base, step, and counter-flashing properly integrated with tiles

4. Verify pipe penetration flashings are lead or copper, shaped to tile profile

5. Check that all flashing extends under tiles on uphill side

6. Confirm sealant is used sparingly and appropriately (not as primary waterproofing)

- Lightweight flashing damaged by tile weight — must use heavier gauge

- Flat flashing under profiled tiles — gaps allow wind-driven rain

- Pipe boots designed for shingles — don't seal against curved tile surface

Per manufacturer specifications, ridge and hip tiles must be bedded in mortar (Type M or S, or flexible polymer adhesive) and mechanically fastened. Ridge must allow ventilation if attic is vented (dry ridge system or vented ridge tiles). Hip tiles must follow the hip line precisely with consistent spacing.

1. Verify ridge tiles are bedded in flexible mortar or adhesive AND mechanically fastened

2. Check that ridge ventilation is maintained if required (dry ridge system)

3. Confirm hip tiles are aligned and properly bedded from bottom to top

4. Verify mortar coverage is complete at joints — no gaps for water entry

5. Check end tiles at ridge/hip terminations are properly sealed

6. Inspect mortar/adhesive for cracks (rigid mortar cracks with thermal movement)

- Mortar only (no mechanical fastening) — ridge tiles blow off in storms

- Rigid mortar cracks with thermal expansion — use flexible adhesive instead

- Ridge blocks ventilation — attic overheats, condensation forms