Leak Causes
HVAC & Equipment Curb Leak Repair
Rooftop HVAC units sit on a curb that penetrates the roof — and ductwork penetrations nearby add more potential failure points.
Rooftop HVAC and other mechanical equipment typically sits on a raised curb, similar in concept to a skylight curb, with the roof membrane flashed up and over the curb edge. Ductwork or refrigerant lines running from the unit down into the building create additional penetrations, each needing its own seal.
A recurring pattern: equipment gets removed or replaced over the years (an old AC unit swapped out, for example), and the roof penetration isn’t always properly re-flashed afterward — sometimes just patched over with whatever was on hand at the time, including mismatched materials that don’t bond properly to the existing membrane.
A proper repair means addressing the actual curb flashing and any associated penetrations as a complete system, not just sealing the visible gap. If a roof has had equipment changes over the years, it’s worth having those areas specifically inspected even if they’re not the current leak location.
What to Check When Equipment Has Been Replaced Over the Years
If your property has had HVAC or other rooftop equipment replaced at any point, it’s worth specifically asking whether the roof penetration was properly re-flashed during that swap, or just patched around the new equipment’s base. Equipment installers aren’t always roofing specialists, and re-flashing a curb correctly isn’t always part of their standard process.
This is a common enough gap that we specifically check curb flashing condition around any rooftop equipment during inspection, particularly if we know or suspect the equipment has been replaced since the roof was originally installed.
Common Questions
Who’s typically responsible for re-flashing a roof curb after HVAC replacement, the roofer or the HVAC company?
Ideally this is coordinated between both, but in practice it sometimes falls through the gap between trades. This is exactly the kind of thing worth confirming explicitly during any HVAC replacement.
Can a leaking equipment curb be fixed without removing the equipment?
Often yes, if there’s enough access around the equipment’s base to properly address the flashing without full removal, though this depends on the specific installation.
Suspect This Is Your Leak?
We diagnose the exact cause before recommending any repair.