Why Rooftop HVAC Curbs Cause Most Savannah Retail Roof Leaks

What Is a Roof Curb, and Why Does It Leak?

A roof curb is a raised, boxed frame built into the roof deck that a rooftop HVAC unit sits on. It lifts the unit above the drainage plane so water runs around it instead of under it. The curb is wrapped with roofing membrane, capped with metal counterflashing, and sealed where the unit's base meets that cap.

That last part is where things go wrong. Unlike the open field of the roof, which is machine-welded or mechanically fastened in long uniform runs, a curb detail is assembled by hand around an irregular shape, usually with sealant doing some of the work. Sealant is the shortest-lived material on the roof. It shrinks, hardens, and cracks in five to ten years of Savannah sun while the membrane beside it still has fifteen years left.

Add the movement factor. An HVAC unit vibrates constantly while running and expands and contracts with temperature. That motion works at the counterflashing and the fasteners holding it. Once the cap lifts even slightly at a corner, wind-driven rain gets underneath, and coastal Georgia has plenty of that.

Why Retail Buildings Get Hit Hardest

Retail centers are built for tenant flexibility, and that means every suite gets its own independently controlled HVAC unit. A twelve-suite strip center in Pooler or on Abercorn can easily carry fifteen or more rooftop units. A warehouse of the same square footage might carry three.

More units means more curbs, more counterflashing, more sealant joints, and more condensate lines discharging onto the membrane. It also means far more foot traffic. Every filter change, belt replacement, and refrigerant check puts a technician on that roof, and technicians tend to approach a unit from the same side every time. Over years, that path compresses insulation and scuffs membrane in a predictable line leading to each unit.

Then there is tenant turnover, which is the part owners underestimate. When a space changes hands, the new tenant frequently swaps or adds rooftop equipment during build-out. That new curb gets cut and flashed on the build-out schedule by whoever the tenant hired. The quality of that detail varies enormously, and it is now a permanent part of your roof.

Why the Leak Never Shows Up Where the Problem Is

This is the single most common source of frustration for property managers, and it is worth understanding before you approve a repair.

Water entering at a curb does not drop straight down. It runs along the top of the roof deck, follows a deck flute or a joist line, and exits through the first available opening, which might be a light fixture, an HVAC diffuser, or a seam in the ceiling grid thirty feet away. A roofer who patches directly above the visible stain has a good chance of patching a perfectly sound section of roof.

Tracing it properly means starting at the interior evidence, working back along the deck structure, and inspecting every curb, penetration, and drain uphill of that path. On a retail roof, that inspection usually ends at a curb. When we run a commercial roof inspection, the report identifies the specific detail that failed rather than the spot where the water landed, because those are two different places and only one of them needs repair.

What Actually Fixes a Leaking Curb

A proper curb repair is not a bead of sealant. It involves pulling the counterflashing, inspecting the curb wrap and the insulation inside the curb for saturation, replacing wet insulation, rebuilding the membrane flashing up and over the curb with new material, and installing new counterflashing with correct fastener spacing and a termination bar where the detail calls for one.

If the insulation inside the curb is soaked, sealing the outside traps that water against the deck. On steel deck, that is how a leak becomes a structural repair.

There is also a coordination question that comes up on roughly half of these repairs. If the unit above the curb is at the end of its service life, is undersized, or is discharging condensate straight onto the membrane, fixing the roof detail alone buys a year or two at most. The efficient move is to lift and service or replace the unit while the curb is already open. On centers in our service area we regularly coordinate that with the mechanical crew at Coastline Heating & Air, so the unit comes off, the curb detail gets rebuilt from the deck up, and everything is reset in one mobilization. One crane day beats two.

How to Stop Curb Leaks Before They Start

Curbs are one of the few roof problems that preventive maintenance genuinely solves, because the failure is slow, visible, and cheap to address early. On the retail centers we maintain in Savannah, Pooler, and Richmond Hill, the routine is straightforward:

• Inspect every curb twice a year, before and after storm season.
• Reseal cracked or shrinking counterflashing sealant on a schedule instead of waiting for a leak.
• Verify condensate lines discharge to a drain rather than onto the membrane.
• Install walk pads along the service paths technicians actually use.
• Walk the roof after every tenant build-out and document any new penetration.
• Clear roof drains so standing water never sits against a curb base.

That last one matters more in coastal Georgia than most owners expect. Ponding water beside a curb keeps the flashing wet for days after a storm, and constantly wet sealant fails years early.

Our CoastalCare Roof Protection Plan covers exactly this scope on a set schedule with a written condition report each visit, which also gives property managers dated documentation if a tenant claim ever comes up.

Talk to a Locally Owned Retail Roofing Contractor

Coastal Roofing of Georgia is locally owned and family operated, and we work on retail centers throughout Savannah, Pooler, Richmond Hill, Rincon, Garden City, Hinesville, and Statesboro. If you have water over a tenant space, we will trace it to the actual source and put the finding in writing before anyone talks about scope or price.

We cover the full scope on our retail and shopping center roofing page, or call (912) 312-0507 for a free inspection.