Membrane Leak After Rooftop Equipment Install Decision Tree
Why this matters
A low-slope membrane that was watertight until an HVAC unit, satellite mount, solar array, or new conduit went in, then started leaking, almost always leaked because of the equipment work, not a coincidental membrane failure. Trades that are not roofers routinely fasten through membranes, walk and gouge them, dam drainage with new curbs, or set equipment without proper flashing, then leave. The leak shows up near the new work but the entry can be offset because water tracks under the membrane along insulation joints. This tree assigns the leak to the correct equipment-related mechanism (penetration, curb/flashing, traffic damage, or drainage obstruction) so the right party is held responsible and the right detail is rebuilt, instead of blaming an aging roof that was fine last month.
Symptom presentation
The interior leak begins after a rooftop equipment installation, near or downhill of the new unit. On the roof you may find new fasteners or anchors through the field membrane, an equipment curb or stand set without proper flashing or counter-flashing, gouges and scuffs along the path the installers walked or dragged equipment, sealant smeared as a substitute for a flashed detail, or new equipment and conduit blocking drainage so water now ponds and backs up to a lap. Timing tied to the install date is the defining clue.
Quick checks
Establish that the roof was dry before the equipment work and confirm the install date against leak onset. Inspect all new penetrations, anchors, and curbs for proper flashing tied into the membrane versus raw fasteners or surface sealant. Walk the installer's likely path for traffic damage (scuffs, punctures, dislodged seams). Probe field seams with a rounded seam probe; a properly welded TPO or PVC lap resists the probe, while a cold weld, a contaminated lap, or a foot-traffic-dislodged seam opens and is a confirmed entry. Check drainage: did the new equipment, sleepers, or conduit dam the slope toward drains, creating new ponding that backs up to seams? A water level higher than the seam height on a low-slope deck conducts under the membrane. Verify warranty status, since unauthorized penetrations commonly void a membrane manufacturer's warranty, and photograph each defect against the install date for cost recovery before any repair disturbs the evidence.
Rooftop equipment areas carry electrical and mechanical hazards plus fall exposure at the perimeter and at skylights or hatches. Coordinate lockout with the mechanical trade, and use fall protection anchored per OSHA 1926 Subpart M.
Isolation tree
- Are there new fasteners, anchors, or conduit supports driven through the field membrane without a flashed, welded, or properly sealed detail? Raw penetrations are the most common cause; each is a direct entry point.
- Was an equipment curb, stand, or sleeper set without proper base flashing and counter-flashing tied into the membrane? An unflashed or improperly flashed curb leaks at its base, often offset downhill from the curb.
- Is there traffic damage along the installers' path (punctures, gouges, dislodged or contaminated seams from foot traffic and dragging)? Damaged seams and punctures away from the equipment but on the access path are a frequent overlooked cause.
- Did the new equipment or its supports obstruct drainage, creating ponding that backs up to a lap or seam? New ponding that reaches a seam height conducts under the membrane.
- If no equipment-related defect is found near the entry, trace the leak under the membrane: water tracks along insulation joints from a remote penetration to the interior drip, so probe uphill toward the equipment with a controlled flood or electronic leak detection.
Confirming diagnosis
A penetration cause is confirmed when a controlled water test or flood test reproduces the leak at a new raw fastener, anchor, or conduit support. A curb/flashing cause is confirmed when flooding the base of the new curb reproduces the leak and the flashing detail is found incomplete. A traffic-damage cause is confirmed by a located puncture or dislodged seam on the access path that reproduces the leak under test. A drainage cause is confirmed when the new ponding reaches a seam and reproduces the leak that did not exist before the obstruction. Controlled flood testing or electronic leak detection on the suspect area, correlated to the install date, is the deciding evidence and the documentation that assigns responsibility.
Remediation
Rebuild the correct detail to the membrane manufacturer's specification: weld or properly flash every penetration with a target patch or pourable sealer pocket per the system, flash and counter-flash equipment curbs and stands into the membrane, and repair punctures and seams with manufacturer-approved patches and welds. Restore drainage by relocating or elevating obstructions on proper flashed sleepers so the slope sheds to drains. Coordinate with the equipment installer and document the cause for cost recovery and to address warranty status. Flood-test the rebuilt details before closing to confirm the entries are sealed.
References
- IBC Chapter 15, R903 and the low-slope provisions of Chapter 15 for membrane roof coverings and flashing.
- FM Approvals / FM Global Property Loss Prevention Data Sheet 1-29, roof penetrations, equipment supports, and securement.
- ASTM D6878 (TPO) and ASTM D4637 (EPDM), membrane material standards; manufacturer flashing-detail specifications.
- NRCA Roofing Manual: Membrane Roof Systems, penetration, curb, and equipment-support flashing details.