Low-Slope Roof Leak at a Wall Flashing on a Commercial Building
A roofing contractor is called to a one-story retail building with a modified bitumen roof over a lightweight insulating concrete deck. Water is staining ceiling tiles along a masonry wall after every driving rain from the west. The contractor finds the base flashing terminates 6 inches above the roof surface, the counterflashing is caulked to the wall with a bead of sealant that has cracked, and the membrane has a 1-inch blister 18 inches from the wall. The building owner wants a quick repair because a tenant is moving in next week. The contractor's foreman proposes cutting out the blister, patching it, and re-caulking the counterflashing. The original roof drawings show a two-ply modified bitumen system with a manufacturer's 15-year labor and material warranty still in force.
1. Is the foreman's proposed repair adequate? Explain what the symptoms indicate and what a proper repair should include.
Read the worked answer
No. The leak is at the wall flashing termination, not just the blister. The base flashing height and the cracked sealant on the counterflashing indicate the counterflashing is not mechanically secured and is relying on sealant, which fails. Water is likely entering behind the counterflashing and running down the wall. A proper repair should: remove the failed sealant, mechanically fasten the counterflashing with a reglet or fasteners at the required spacing, install a proper termination bar and sealant detail per the manufacturer's specifications, and replace the base flashing if it is not properly adhered and terminated. The blister should be cut out, dried, and patched per the manufacturer's repair detail - not just covered. Because a 15-year manufacturer warranty is in force, any repair must use the manufacturer's approved materials and details or the warranty may be voided.
2. What should the contractor do about the existing warranty before performing any work?
Read the worked answer
Contact the manufacturer's technical representative and the original installer, and review the warranty terms. Many warranties require that repairs be performed by an approved contractor using approved materials and that the manufacturer be notified. The contractor should obtain written confirmation that the proposed repair method will not void the warranty, document the existing condition with photos, and keep the correspondence in the job file. If the repair is beyond the warranty scope, the contractor should provide the owner a written proposal that distinguishes warranty-covered work from owner-paid work.
3. The owner insists on a one-week turnaround. How should the contractor balance schedule pressure against proper repair and liability?
Read the worked answer
The contractor should not cut corners to meet the tenant move-in date. Provide a written proposal with the proper repair scope, a realistic schedule, and a clear statement that the temporary patch option is not recommended and would not carry a workmanship warranty. If the owner elects a temporary repair, document that election in writing, state its limitations, and schedule the permanent repair. The contractor's license and liability exposure favor documented, code-compliant work over a rushed caulk-and-patch that will fail and generate a callback and potential claim.