Tile, Slate, Metal & Low-Slope Roofs
~12 min read · Know the inspection points and failure modes of non-asphalt coverings and membranes.
Beyond asphalt live the specialty roofs — tile, slate, metal, and the low-slope membranes — each with its own walking rules, failure signatures, and lifespans measured in generations or in ponding seasons.
Tile and slate
Clay/concrete tile and slate are long-life coverings (50–100+ years) whose weak points are the PIECES and the layers beneath: cracked, slipped, or missing units; deteriorated underlayment and flashings that age out long before the covering; and fastener corrosion letting slates slide ('nail sickness'). They are fragile to foot traffic — inspect from the edges, a ladder, or binoculars/drone rather than walking, and say so as a method note. Heavy coverings also demand adequate structure — sagging under tile is a framing question.
- Units crack and slip; underlayment ages out first
- Don't walk them — inspect from ladder/edges and note the method
- Weight requires framing capacity — check for sag
Metal roofs
Standing-seam and screw-down panels last decades; their findings: fastener back-out and gasket decay on exposed-fastener systems (the maintenance treadmill), seam and closure failures, corrosion at scratches, cut edges, and dissimilar-metal contacts (galvanic pairs — copper wash over steel, aluminum against treated lumber), panel oil-canning (cosmetic), and flashing details at penetrations. Movement noise and slope minimums per profile round it out.
- Exposed screws: back-out and dead gaskets = the drip points
- Galvanic corrosion at dissimilar-metal contacts
- Standing seam ages best; check closures and penetrations
Low-slope membranes
Flat roofs (below shingle slope) wear membranes: built-up (BUR) with gravel, modified bitumen (torch/peel), single-ply EPDM (black rubber), TPO/PVC (white thermoplastic, welded seams). Universal findings: ponding water (standing >48 hours — deflection, drains, or design), seam failures (EPDM's glued seams, TPO's weld voids), blisters and alligatoring (BUR/mod-bit aging), punctures, and flashing terminations at parapets and penetrations. Interior ceiling stains below complete the evidence loop.
Worked example
One property, three roofs: a concrete-tile main roof with a dozen slipped tiles and interior stains despite 'tiles rated 75 years'; a screw-down metal porch roof with rust rings around a third of its fasteners; and a flat EPDM garage roof with a birdbath-sized pond and a lifted seam. Report each.
The tile roof: the covering's 75-year rating misleads — slipped tiles expose the UNDERLAYMENT, which is the actual waterproofing and is decades old; interior stains say it has failed. Finding: reset/replace displaced tiles and evaluate underlayment — likely a relay despite healthy tiles; inspected from ladder/edges (method note). The metal porch: fastener gaskets are dying en masse — each rust ring is a future drip; systematic refastening/gasket replacement, and check for galvanic contacts. The EPDM: ponding plus a lifted seam is the leak recipe — reseam and address drainage (added drain/scupper or tapered fix); check the garage ceiling below. Three coverings, one lesson: the covering's lifespan is not the ROOF's lifespan.
Common exam pitfalls
Rating a tile/slate roof by the covering's lifespan.
The underlayment and flashings fail decades earlier — displaced units expose the real (aged) waterproofing.
Walking fragile coverings to 'inspect thoroughly.'
Foot traffic breaks tile and slate — inspect from edges/ladder/optics and disclose the method.
Dismissing ponding as 'flat roofs hold water.'
Standing water past ~48 hours accelerates every membrane's death and finds every seam flaw — report it with cause analysis.
Tiles outlive their bedding, screws outlive their gaskets, membranes drown in their own ponds.
Recap
- Tile/slate: units slip, underlayment is the real clock — don't walk them
- Metal: fastener gaskets, seams, galvanic contacts
- Membranes: ponding, seams, blisters, terminations
- EPDM glued seams and TPO welds are the leak lines
- Interior stains close the evidence loop
- Method and access limitations get stated
Prove it: 10 questions on this topic
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