Roof failure encyclopedia.

UV breakdown of asphalt oils. Surface contracts into a scaly, cracked pattern that resembles alligator skin.

Asphalt, tar & gravel, mod-bit

Repair window: 2–4 years before active leaks. Coating or recovery may extend life.

Trapped moisture or solvent vapor between roofing plies expands when heated, lifting the surface into bubbles.

BUR, mod-bit, occasionally TPO

Small (<2"): monitor. Large or popped: cut, dry, patch immediately.

Seam lap pulls open due to thermal cycling or poor adhesive cure. Water tracks straight under the membrane.

TPO, EPDM, mod-bit

Immediate seam repair — heat weld or new lap. Don't caulk over it.

Thermal expansion + freeze-thaw walks screws back out of decking. Membrane tents around each fastener.

Metal, single-ply mechanically attached

Re-seat with longer/larger fasteners, add stress plates, seal penetration.

Inadequate slope or clogged drains. Standing water over 48 hours doubles UV degradation and voids most manufacturer warranties.

All flat/low-slope

Tapered insulation, additional drains/scuppers, or sump pump in chronic spots.

UV + impact (hail, foot traffic). Exposed asphalt mat ages 3x faster.

Asphalt shingles, mod-bit cap sheet

Light loss + roof <10yr: monitor. Heavy loss + bare spots: replacement plan needed.

Fastener corrosion, broken battens, or impact. Slipped tiles expose underlayment to UV.

Clay, concrete tile

Re-secure or replace tile; inspect/replace underlayment if exposed >6 months.

Sealant failure or galvanic corrosion where flashing meets dissimilar metals. #1 source of leaks at chimneys, walls, skylights.

All

Strip out and re-flash — never caulk-and-pray.

Decking rot from chronic leaks, overloaded snow/water load, or under-spec rafters.

All

Stop work, get a structural engineer. Decking + framing repair before any roofing.

Algae feeding on limestone filler in shingles. Cosmetic, not structural — but unsightly.

Asphalt shingles

Soft-wash with zinc/copper sulfate. Install zinc strip at ridge to prevent recurrence.