Roof waterproofing that seals Jersey City flat roofs end to end

Most leaks we trace on Jersey City flat roofs don't start in the open field of the membrane. They start where something interrupts it: a vent stack, a hatch curb, a parapet base, an old antenna mount, the joint where a rear extension meets the main roof. Patch one of those and the water simply moves to the next weak spot a few feet away. Roof waterproofing treats the field, every edge and every penetration as a single continuous layer, so there is no seam between the repair and the roof around it.

On a pre-war walk-up near Journal Square that can mean a long list of interruptions: plumbing vents, exhaust fans, a bulkhead door, internal drains and a parapet running the full perimeter. A brick rowhouse downtown may have fewer penetrations but a long run of party-wall parapet shared with the neighbors. The approach is the same either way. Our technicians map every detail first, decide how each one will be sealed, and only then choose the liquid-applied system that handles that particular mix of details.

Roof water doesn't stop being your problem at the roof edge, either. Every gallon the membrane sheds goes down the leaders, and on many older buildings those leaders empty right beside the foundation or into a buried pipe that collapsed years ago. One inch of rain on a 1,000 sq ft roof is about 623 gallons. If the basement turns damp after storms, we check where that water lands and, where it fits, carry it away from the walls with underground leader drains.

Sheet goods like EPDM, TPO and modified bitumen cover open roof area well, but every pipe and curb needs a cut, a boot or a field-made patch, and each of those is a lap that can open later. A liquid-applied membrane goes on wet and cures into one skin with no laps at all. That makes it the stronger choice on cluttered roofs: dozens of pipes, conduit supports, odd-shaped curbs, or the corner where three generations of old repairs meet.

We use two main families. Polyurethane membranes are flexible and tough, and they suit larger areas where foot traffic is light. Reinforced PMMA systems cure fast, even in cool weather, and carry a polyester fleece embedded between coats, which gives them strength at details that move with the building. Both need a clean, dry, primed surface. Neither one is paint: a properly built membrane goes on at a measured thickness and is reinforced wherever the roof flexes.

Owners often ask whether a silver or white coating is the same thing. It isn't. A roof coating is a maintenance layer that restores UV protection on a membrane that is already sound and dry. Waterproofing is the water-stopping layer itself, built and reinforced to keep water out without help from what lies underneath. If the existing roof is wet across most of its area, neither one is the answer: that membrane has reached the end of its life and needs replacing, and the parapets and details around it get waterproofed into the new surface.

The difference shows at the details. On a waterproofing job, flashing heights are checked, base flashings are wrapped or rebuilt, termination bars are set at the top of every upturn, and fabric goes into every inside and outside corner before the full coats. That work is slow and unglamorous, and it is where most of the labor goes. It overlaps heavily with flashing repair, and the details we always cover include:

• Reinforcing fabric at every inside and outside corner
• Pipe and conduit penetrations wrapped and collared
• Parapet bases run up and terminated under a bar or coping
• Curbs on hatches and rooftop units fully wrapped
• Drain bowls clamped or stripped into the new membrane
• Transitions between old and newer roof sections bridged

On roofs with internal drains or scuppers, we flood test a section once the membrane has cured. Drains in that area are plugged, an inch or two of water is held against the new work, and someone checks the ceiling below for any sign of moisture. One inch of standing water weighs about 5.2 lb per sq ft, so we test in sections the structure can comfortably carry, never the whole roof at once.

We also photograph each detail before it is covered, so you have a record of how the parapet bases, drains and penetrations were built. If you manage a condo or co-op building, that record helps when the board weighs this work against other repairs, because it shows what condition the deck and insulation were in when the membrane went on. Owners planning a rooftop deck should read how a deck treats the roof underneath before any framing goes down.