Wall Termination at Masonry and Two Marginal Pipe Boots
A 12,000 sq ft fully adhered EPDM roof is being installed on a low-slope building with a brick masonry wall on the north side. At that wall, the crew runs the membrane 5 in. up the brick, attaches an aluminum termination bar with fasteners at 24 in. o.c., and beads solvent-based lap sealant along the top edge. Existing through-wall flashing with open weep holes sits 10 in. above the new roof surface, and no counterflashing was specified. Two penetrations also need attention: a 6-in.-diameter PVC vent pipe fitted with a pre-molded boot listed for 2-in. to 6-in. pipe and secured with one stainless clamp, and a 2-in. conduit with a boot that is visibly too large, packed with lap sealant and no clamp. The building is in a freeze-thaw climate with wind-driven rain on the north wall. The owner's representative asks whether the wall detail just 'needs the sealant redone' as the only fix.
1. Evaluate the wall termination: identify each nonconforming element and explain what water will do to it.
Read the worked answer
Four separate defects, and the sealant is the least important of them.
Height. Five inches is below the height normally required for base flashing, which is at least 8 in. above the roof surface. There is no reliable lap above the splash and snow line, and the termination sits below the through-wall flashing at 10 in.
Fastening. Termination bar fasteners at 24 in. o.c. will not hold the bar tight enough to compress the membrane uniformly. The bar gaps between fasteners, water enters behind it, and the gap widens with thermal cycling. Typical practice is fasteners at 6 to 8 in. o.c. with the appropriate fastener for the substrate.
Sealant as the primary seal. Lap sealant at the top edge is a secondary detail. It is not a substitute for elevation, mechanical termination, and counterflashing. In a freeze-thaw climate with wind-driven rain, a solvent sealant bead on brick will crack and lose adhesion within a few seasons, and once it opens, water goes directly behind the membrane.
No counterflashing and no relationship to the through-wall flashing. The correct termination rises above the through-wall flashing line, and counterflashing covers the top of the base flashing so water in the wall drains out through the weep holes above the roof flashing rather than behind it. As built, wall water and rain can run down behind the base flashing.
Answer to the owner's representative: no, redoing the sealant fixes none of this.
2. Describe the correct sequence for rebuilding the wall flashing detail.
Read the worked answer
Rebuild from the deck up, and sequence the masonry work with the membrane work.
Establish the termination height. Base flashing should extend at least 8 in. above the roof surface and above the through-wall flashing line, so the new termination lands above 10 in. here. Determine that elevation on the wall before cutting anything.
Remove the existing termination bar, membrane flashing, and old sealant. Inspect the brick and the through-wall flashing; repair deteriorated mortar or spalled brick, and confirm the weep holes are open and will remain above the new flashing.
Install the membrane flashing with a proper adhesive or the manufacturer's flashing system, dressed tight to the wall with no bridging, and extend it to the termination elevation.
Install the termination bar with fasteners at the manufacturer's spacing, typically 6 to 8 in. o.c., using fasteners suited to the substrate. Seal the top edge of the bar with lap sealant as a secondary detail only, and keep the sealant bead small enough that it does not trap water.
Install counterflashing above the termination, in a reglet or surface-mounted, lapping over the top of the base flashing and terminating above the through-wall flashing so the weep holes stay clear. Leave the bottom edge of the counterflashing free to drain.
Verify weep holes are open and functioning after the counterflashing is installed; this is the step most often missed.
3. For the 6-in. PVC pipe and the 2-in. conduit, what is wrong and what is acceptable? How do you verify the finished penetrations?
Read the worked answer
Neither penetration is acceptable as described, for different reasons.
6-in. PVC pipe. A boot listed for 2 to 6 in. is being used at the extreme top of its range, so the cone is stretched to its limit and the sealing band that should compress against the pipe is stretched thin; a single clamp at that stretch does not produce uniform contact, and the boot may not have enough slack to accommodate pipe movement. Acceptable: a boot sized for the pipe, ideally with the pipe diameter centered in the listing rather than at the limit, installed over a clean pipe with the flange fully adhered or mechanically clamped to the deck and flashed into the membrane, with clamp(s) per the manufacturer. Confirm the boot material is compatible with the pipe and the vented contents, and confirm the pipe is rigid and properly supported so it does not move the flashing.
2-in. conduit. A boot that is visibly too large, with sealant packed around it and no clamp, is not a flashing. Sealant alone is never a primary seal at a penetration. Acceptable: a correctly sized pre-molded boot with a clamp, or a molded/applied flashing detail appropriate for a small pipe, fully adhered to the membrane and clamped to the conduit.
Verification: water test both penetrations, with the test held long enough to reveal a slow leak at the clamp line, and inspect from below if accessible. Photograph the finished details. Also confirm each boot and flashing product is the one specified and is within its listed size range, and record the listing used.