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Common Causes of Commercial Roof Leaks
Commercial roof leaks rarely start where the water shows up inside — water travels along decks and beams before it drips. Knowing the usual suspects lets a property manager find the real source faster and prevent the next one.
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1. Flashing failures
The top cause, full stop. Flashing — the metal transitions at walls, curbs, parapets, and penetrations — takes the most thermal and wind stress on the roof. Colorado's freeze-thaw cycling works joints open season after season. Failed pipe boots (cracked rubber collars) alone account for a huge share of commercial leak calls.
Prevention: include every flashing point in each inspection (see our inspection checklist for property managers).
2. Open seams
On single-ply membranes (TPO, EPDM, PVC), seams are the weak link — especially adhered EPDM seams as they age. Thermal cycling, foot traffic, and ponding water all stress them. Heat-welded TPO/PVC seams hold up better, but poor original welding still fails.
Prevention: probe-test seams during inspections; repair at the first sign of fish-mouthing — not after the leak.
3. Ponding water
Water standing 48+ hours accelerates every failure mode: it degrades membranes, pries at seams, and adds tremendous structural load. Ponding usually means drainage failure — clogged drains, settled insulation, or original slope that's no longer adequate.
Prevention: keep drains clear and address new ponding promptly. Details in how ponding water affects flat roofs.
Talk to a Colorado roofer. Chasing a leak in your building? One call connects you with an independent commercial roofing professional who finds the real source — not just the stain.
4. New penetrations
Every new rooftop unit, vent, antenna, or solar mount is a new hole in a waterproof system. The leak often appears months later when the improperly flashed curb finally gives way. Rule: any trade that penetrates the roof must coordinate with the roofing contractor, and every penetration gets proper flashing — not just sealant.
5. Storm damage and age
- Hail: Punctures membranes and fractures aged surfaces. Thicker membranes (60/80-mil) resist better.
- Wind: Lifts edge metal and loosens flashing; once the edge goes, the field follows.
- Age: Every system has a service life. Alligatoring, widespread blistering, and brittle membranes mean the roof is telling you it's done — see warning signs of membrane failure.
When age is the cause, the honest fix is commercial roof replacement — not another round of patches.
FAQs
Why does the leak show up far from the actual problem?
Water runs downhill along the deck, beams, and insulation before finding a path inside. The stain marks the exit, not the entrance — tracing requires a roof-level inspection.
Can I just seal a leak with caulk?
As an emergency stopgap. As a repair, no — sealant over a failed seam or flashing fails again. Fix the component properly.
How fast should a commercial leak be addressed?
Immediately for active leaks — every day of water intrusion damages insulation, deck, and interiors. Temporary dry-in first, permanent repair second.
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