Corner Peel-Back on a Mechanically Attached Warehouse Roof
A 24,000 sq ft warehouse in a dusty industrial park receives a mechanically attached 60-mil EPDM roof: 10-ft-wide sheets, fasteners with 2-in. seam plates at 12 in. o.c. along the seams, and an enhanced perimeter row at 6 in. o.c. Field seams are made with 6-in. pressure-sensitive splice tape. The crew does not use splice cleaner, arguing that the membrane is new and came off the pallet clean; they roll seams with a 2-in. hand roller, and the daytime temperature during seaming is 48 F. Six weeks later, a storm with measured 85 mph gusts peels back a 20 ft by 30 ft section at a building corner. The membrane separated along the seam between the first and second sheet. The tape shows a clean adhesive transfer with visible dust embedded in the adhesive. There are no membrane tears or elongated holes at the seam plates, and every fastener and plate is still in the deck. The owner wants the contractor to 'add more fasteners' and reinstall the peeled membrane.
1. Based on the physical evidence, is this a fastener or wind-uplift problem or a seam problem? Explain the reasoning and identify contributing factors.
Read the worked answer
This is a seam failure that let uplift into the assembly; the fasteners did their job.
Reasoning from the evidence: the membrane released along a seam, not at the plates. Every fastener and plate is still in the deck, and there are no elongated holes or tears at the plates, which is what you would see if the membrane had been pulled over fastener heads or if the plates had insufficient bearing. So the attachment was not the initiating failure. The clean adhesive transfer on the tape means the tape bonded to the membrane and then released cohesively/adhesively rather than the membrane tearing around the seam, which points to a weak bond line, not a strong wind-only event. Once the corner seam opened, the membrane acted as a sail and the peel ran 20 by 30 ft.
Contributing factors, all visible in the setup:
- No splice cleaner on a dusty site, with dust now embedded in the adhesive. Splice cleaner is a required step, and 'new membrane' is not a substitute for it; factory surfaces still carry talc, dust, and handling contamination.
- 48 F seaming is at the low end for pressure-sensitive tape; tack and wet-out drop with temperature.
- A 2-in. hand roller over a 6-in. tape is unlikely to have delivered the uniform pressure the tape needs; the middle of the lap is the usual void.
- Confirm whether the corner zone itself was enhanced, not just the perimeter row at 6 in. o.c. Corner uplift demand is the highest on the roof.
'More fasteners' would leave the actual defect in place and would not have prevented this.
2. Write the repair scope for the damaged corner, including what must not be reused.
Read the worked answer
Repair the area as a new corner, not as a patch of the old one.
- Remove the peeled membrane back to sound, fully adhered material beyond the visible damage, and remove the failed seam tape entirely. Do not re-bond over old tape or old adhesive.
- Inspect the exposed substrate and insulation. Replace any insulation that is wet, crushed at the plates, or has enlarged fastener holes. Verify the deck is sound and dry.
- Do not reuse the existing fastener holes. New fasteners go in new locations at the spacing and pattern required for the corner zone per the manufacturer's uplift design for this deck type and wind speed, using fasteners and plates approved for the deck. Existing plates that stay in place must be verified, not assumed.
- Install new membrane with new seam tape, using splice cleaner on both surfaces, fresh tape within shelf life, and a seam roller of adequate width with the manufacturer's required pressure. Seam only above the manufacturer's minimum temperature, or use the approved cold-weather procedure.
- Treat the corner as a corner: verify the corner enhancement is actually installed, and consider adhered or additional mechanical securement at the corner if the original design did not specifically address it.
- Water test or visually verify all new seams after they cure, and document with photos and a seam map.
3. What quality-assurance program do you run on the remaining seams and attachments before signing off on the whole roof?
Read the worked answer
The failure mode is a workmanship failure, so the QA has to sample workmanship, not just count fasteners.
Seams:
- Probe every field seam the day after seaming with a seam probe or dull screwdriver, looking for voids and unbonded edges along the full length. Probe the laps that were made on the same days and by the same crew as the failed seam first.
- Perform destructive seam pull tests at a frequency the manufacturer recognizes, typically cutting samples from representative seams, and repair each test location properly. If failures appear, escalate sampling rate and consider reworking the seams.
- Verify tape records: product, lot, shelf life, and that splice cleaner was used. If cleaner was skipped generally, assume the affected seams are suspect until tested.
Attachment:
- Confirm as-built fastener spacing against the approved uplift plan, including that perimeter and corner zones were enhanced as designed, not just the field spacing.
- Check plate seating and any pull-through or elongated holes; confirm fastener type and length are correct for the deck and that engagement meets the manufacturer's requirement.
Documentation: retain test results, photos, and a seam map, and get the manufacturer's representative to review the probe and pull-test results before final acceptance. Advise the owner in writing that seams made without cleaner are a known risk area and schedule an inspection after the next significant wind event.