Rooftop HVAC Units and Roof Leaks in Orange County
Rooftop HVAC units are the most common source of roof leaks on Orange County commercial buildings, and a growing one on homes with package units. The unit itself rarely leaks. What fails is everything around it: the curb it sits on, the condensate line dripping beside it, the ducts and line sets that punch through the membrane, and the roof surface worn down by every technician who walks out to service it. This guide covers each of those failure points and how to get the roofer and the HVAC contractor working together instead of pointing at each other.
Curb Flashing: Where Most HVAC Leaks Start
A rooftop unit sits on a curb, a raised box framed into the roof. The membrane must run up the side of that curb, terminate under a counterflashing or cap, and be sealed at the corners. Leaks happen when the curb is too short, so ponding water or wind-driven rain simply tops it; when the membrane was cut and lapped at the corners instead of being wrapped with a proper corner patch; or when the unit was set with no cricket on the uphill side, so water pools against the curb during every winter storm. A curb should stand well above the finished roof surface, and on a low-slope roof a cricket behind it is not optional. Our overview of Roof Penetration Leaks in Orange County: Vents, Pipes, and HVAC Curbs explains why penetrations fail before the field does.
Condensate Lines That Rot the Roof Around Them
Every air conditioner produces condensate, and on a rooftop unit that water has to go somewhere. Too often it goes straight onto the roof. A line that terminates on the membrane keeps a patch of roof wet all summer, which grows algae, softens asphalt-based surfacing, and creates a shallow pond that never dries. That pond is exactly where the membrane ages fastest and where the first seam opens. The fix is to route the condensate to a roof drain, scupper, or dedicated drain line, and to support the pipe on blocks rather than laying it directly on the surface where it traps debris. Where a pond has already formed, Flat Roof Ponding Water in Orange County: Causes and Permanent Fixes covers how the low spot is corrected.
Duct and Line-Set Penetrations
Supply and return ducts on a curb-mounted unit pass through the curb opening, which is protected. Problems come from everything added later: refrigerant line sets, electrical conduit, gas lines, and thermostat wiring that were pushed through the roof wherever it was convenient. These are often sealed with nothing but a blob of mastic that cracks in the first summer. Each one needs a proper pitch pocket or a pre-formed boot with a clamped collar, and grouped penetrations are better run through a single flashed sleeve than through five separate holes. When we find a roof with a dozen unflashed penetrations from years of tenant improvements, that is usually the whole leak story.
Technician Foot Traffic and Walk Pads
An HVAC unit that gets quarterly service sees a technician, a tool bag, and sometimes a replacement compressor dragged across the same path every visit. On TPO and PVC that means scuffs and eventual punctures; on modified bitumen it grinds off the granules; on foam it crushes the surface coating. Add screws and sheet-metal offcuts left behind after a repair and you have a puncture waiting for the first foot. Walk pads from the roof hatch or ladder to each unit, and a service perimeter around the unit, are the cheapest leak prevention available on a flat roof.
Coordinating the Roofer and the HVAC Contractor
The most expensive HVAC leaks happen during unit replacements. The HVAC crew arrives with a crane, sets a new unit that does not match the old curb footprint, and either shims it or drops in a curb adapter, and nobody flashes the result. Then it rains. The right sequence is: roofer inspects the existing curb and flashing before the swap, raises or rebuilds the curb if it is too low, the HVAC crew sets the unit and adapter, and the roofer returns to tie the membrane into the new curb the same day. Rescue Roofer regularly schedules alongside HVAC contractors on commercial jobs so the roof is never left open. For leaks that are already interrupting a business, see Commercial Roof Leak Repair in Orange County: Minimize Downtime.
Residential Package Units on Orange County Homes
Package units, where the whole system sits on the roof instead of splitting between an attic furnace and a ground condenser, are common on 1950s to 1970s homes with low-slope sections in cities like Garden Grove, Westminster, and Costa Mesa. The same curb, condensate, and penetration rules apply, but with a twist: many of these units sit on a wood platform on a shingle or rolled roof, and the platform legs were never flashed at all. Water runs down the legs and into the deck. When a homeowner tells us the ceiling stains only in summer, a package unit condensate line or an unflashed platform leg is where we look first.
Why Work With Rescue Roofer
Rescue Roofer has been licensed since 1993 (C-39, St. Lic #1137524), bonded and insured, with T.E.A.M. certified technicians who work on commercial flat roofs and residential low-slope roofs every week. Our 4-Phase Roof Inspection produces a 6–7 page photo report that identifies every curb, penetration, and condensate discharge on the roof, so you know exactly what needs attention before any work is approved. We use synthetic underlayment only, coordinate directly with your HVAC contractor, and back every repair with a written workmanship warranty.
Related reading: Commercial Flat Roofing in Orange County | Restaurant Roof Repair in Orange County: Grease, HVAC, and Health Codes | Commercial Roof Inspection in Orange County
Frequently Asked Questions
The leak is right under our rooftop AC unit. Is it the roofer's problem or the HVAC company's?
It depends on where the water is entering. A cracked cabinet, a loose panel, or a failed drain pan inside the unit is HVAC work. A failed curb flashing, a torn membrane around the curb, or a leaking duct penetration is roofing work. Rescue Roofer traces the entry point first so the right trade fixes it and you are not paying for two service calls.
Can a condensate line really damage a roof?
Yes. A line that dumps onto the membrane keeps one spot wet year-round, which breeds algae, softens the surfacing on modified bitumen, and creates a permanent pond that eventually finds a seam. Condensate should be piped to a drain or scupper, never left to drip on the roof.
Do we need walk pads on our flat roof?
If technicians service equipment on the roof more than a few times a year, yes. Dropped tools, dragged parts, and repeated foot traffic on the same path are a leading cause of punctures around HVAC units. Pads are inexpensive compared with the leak repair they prevent.
We are replacing our rooftop unit. Should a roofer be involved?
Yes, before the crane arrives. A new unit often has a different footprint and needs a curb adapter or a new curb, and the membrane must be tied into that curb correctly. Having the roofer flash the curb while the HVAC crew sets the unit avoids a leak that shows up the first time it rains.
Need a roofer in Orange County? Call 1-888-346-7663 for a free roof assessment — or request one online. Rescue Roofer has served Orange County since 1993. St. Lic #1137524.