A failed seam is the single most common place a Winchester, KY commercial flat roof actually leaks — more often than a puncture, a curb, or a drain — because a TPO, PVC, or EPDM membrane is really a field of sheets joined edge to edge, and every one of those joints is a potential failure point.
Why Do TPO, PVC, and EPDM Seams Fail?
Seams fail from incomplete original welding or adhesion, or from years of thermal cycling and foot traffic working the joint loose — not usually from one single event.
TPO and PVC seams are heat-welded, fusing the two sheets into one; EPDM seams are typically bonded with adhesive tape or liquid adhesive rather than welded. A weld that ran too cool, too fast, or over a dirty or wet membrane during original installation never fully fused, and it shows up as a failure months or years later rather than immediately. On seams that were installed correctly, the usual cause is age: the membrane expands and contracts with every hot afternoon and cold night, and that constant movement eventually works even a good seam loose, especially near parapets, curbs, and other spots with less flexibility. The National Roofing Contractors Association lists seam integrity as one of the specific items a proper roof inspection probes by hand, since a seam that looks fine from a walk-by can still be open underneath.
Can a Failed Seam Be Repaired, or Does the Whole Membrane Need Replacing?
A localized seam failure is almost always a repair, not a replacement — patching or re-welding a section of seam on a small commercial building typically runs $300–$1,500.
The exception is a membrane with widespread seam failure across many joints rather than one isolated spot — that points to a systemic installation or age problem, and repeated seam repairs across a large roof area move into the $1,500–$7,500+ range for larger sections, the same bracket as other extensive membrane repair work. Either way, the fix has to match the original membrane type; a TPO patch heat-welded onto TPO holds, but the wrong material or method on top of an incompatible membrane just creates a second failure point. Our roof leak detection visit is where we probe seams by hand to find out whether it’s one joint or a pattern before quoting anything.
How do you find a failed seam if there’s no visible leak yet?
By hand-probing seams during inspection, especially near parapets, curbs, and drains, since a seam can be open underneath before it shows up as an interior leak.
Can EPDM seam tape be used to patch a TPO seam?
No — repairs need to match the original membrane’s material and bonding method, since mismatched materials generally won’t form a lasting bond and create a new failure point.
Does one failed seam mean the whole roof needs replacing?
Not usually — an isolated seam failure is typically a targeted repair; replacement becomes the conversation only when seam failures are widespread across the roof.
Not sure if what you’re seeing is a seam issue or something else? Get a free estimate or call or text (859) 310-1209.
Related: Flat Roof Repair | Roof Leak Detection | TPO vs. EPDM vs. PVC
Source: National Roofing Contractors Association.
Last updated: September 13, 2026