Skylight and Penetration Flashing in Brockton, MA
Skylights get blamed for leaking. The glass or acrylic dome is rarely the problem. The leak is at the curb, where the skylight frame meets the roof. That joint moves with temperature, settles with the building and sits in a spot where water collects. Pipe boots, vents and curbs for rooftop units share the same weakness. Every hole in a roof is a flashing, and every flashing is a place the roof can fail.
Brockton, MA gives these details a hard life. About 34 inches of snow a year, a record low of minus 19 degrees Fahrenheit and repeated freeze and thaw open any joint that is only sealed. We rebuild flashing so it holds through winter, not just through the next rain.
Rebuild the Curb Flashing, Not the Skylight
A skylight curb is a box around a hole in the deck. Membrane runs up the sides of the box and is capped at the top. The weak points are the corners, where the membrane folds, and the top edge, where it is sealed to the frame. Sealant dries and cracks. Corners open. Water runs in behind the membrane and down inside the curb.
We cut out failed flashing and rebuild it with new membrane. Corners get a formed patch or a welded cover. The top edge gets a metal termination and sealant. If the curb itself is rotted, we repair or replace it. We test the finished flashing before the crew leaves. Fixing the flashing is almost always cheaper than replacing the skylight.
Pipe penetrations follow the same pattern at a smaller scale. A boot is a collar that fits around a pipe and laps onto the membrane. The collar cracks. The clamp loosens. Water runs down the pipe and into the ceiling, often at a spot far from the pipe. On a thermoplastic roof, we weld a new pre-molded boot over the pipe. On other systems, we use the matching boot and seal the base. Large or odd shapes get a field-built pocket.
Distrust the Sealant Line
A tube of sealant is the usual repair. It works for a season. Then the roof moves, the sealant lets go and the leak is back. The crack in the sealant looks like the cause. It is not. The cause is that the joint moves and the sealant cannot flex enough.
We look at what moves and why. A pipe that expands in summer pulls the boot with it. A curb that settles with the building pulls its flashing. A frame that warms and cools rubs against its seal. The fix is a detail that allows for that movement: a welded boot with a stainless clamp, a membrane flashing with slack, or a counterflashing that laps over the roof flashing and sheds water. Sealant supports a good detail. It does not replace one.
Check Each Opening on the Roof
A roof plan should list every penetration. Each one has its own risk.
- Pipe boots, cracked rubber or loose clamps
- Vent stacks and goosenecks, rust or loose collars
- Skylight and smoke hatch curbs, open corners
- Rooftop unit curbs, failed flashing or low height
- Conduit and gas line supports, rubbing the membrane
- Roof hatches and ladders, gaps at the frame
We count them on the first walk. Roofs that have grown over the years collect abandoned penetrations from old equipment. Those get capped and flashed or removed. Every opening we close is one fewer leak path.
Height is the other check. Flashing must rise above the roof surface high enough that ponded water or snow cannot reach the top edge. Local practice and manufacturer rules set the minimum. Where a flashing sits low, we raise it or add a saddle to drain water around it. A detail that is tight but low will leak the first time water stands against it.
Decide Between Re-Flashing and Replacing the Unit
Old skylights add a second question. A dome that has yellowed and crazed has finished its service life. A frame that is corroded or cracked will not hold a new seal. In those cases, replacing the skylight with the flashing is smarter than flashing around a dead unit.
Some owners want skylights removed. We can deck over the opening, insulate it and tie the roof in. That removes the leak path for good. Daylighting and code needs differ by building, so the owner decides. When a unit stays, we check that the curb height meets the manufacturer's minimum above the roof surface. Low curbs flood in a heavy rain. A curb under mechanical equipment gets the same treatment as rooftop equipment curbs and supports.
Smoke hatches and roof hatches are a special case. The frame, the cover and the gaskets all wear, and a hatch that does not close tight lets in rain and air. We check the gasket, the hinges and the curb. Repair is usually possible, but a hatch that has bent or rusted through should be replaced with its curb flashing.
Account for Snow Drift and Ice Around Penetrations
Snow drifts against curbs and builds depth on the uphill side. Meltwater sits against the flashing for days. Ice forms and lifts the termination. Brockton averages 14.3 mph of wind, so drifts build fast around anything that sticks up.
We set flashing heights with snow in mind. Higher curbs and well-sealed terminations stand up to drift loads. We also keep pipe boots clear of drain paths so meltwater does not flow into them. After a heavy storm, we check penetrations first. A flashing failure repair in January is harder than in October, so the fall visit matters.
Cold shrinks sealant and stiffens rubber. A boot that sealed well in July can gap in January. That is why we use materials rated for low temperatures and we prefer welded or formed details over caulked ones. Details that rely on adhesion alone are the first to open in a cold snap. Details with a mechanical termination hold.
Trace the Leak Back to the Opening
A leak near a penetration is easy to guess at and hard to prove. We run a hose test, one detail at a time, from the bottom up. When the leak shows, we have the answer. This is the method behind any commercial roof leak repair, and it avoids paying to fix the wrong detail.
Waiting costs money. Water that enters at a curb soaks insulation around it and then spreads. On a hospital or a school, a leak near a skylight can wet a clean space or a classroom. In buildings like the Brockton VA, with more than twenty structures, each roof has its own openings. We list them building by building. Property managers in Easton, Stoughton and Brockton get the same list format, so repair priorities can be compared.
A roof with many openings costs more to maintain. Every one adds a seal that can fail. A job that adds roof insulation and cover board is a good time to cut the count, since the roof is open and abandoned penetrations can be removed. Fewer holes mean fewer leaks.
Commercial Roofing Questions
Why does my skylight leak only in heavy rain?
Water reaches the failed spot only when it is deep enough or driven by wind. A hose test finds the exact opening.
Can a leaking skylight be fixed without replacing it?
Usually, yes. Most leaks come from the curb flashing. We rebuild that and leave the unit if it is sound.
What is the lifespan of a pipe boot?
Rubber boots crack in sun and cold, often well before the roof wears out. We replace them with longer-lasting boots or build a welded pocket.
Can you remove a skylight and close the roof?
Yes. We frame and deck the opening, add insulation and tie in the membrane. Interior finish work is separate.
Do you flash around new equipment?
New openings get a curb, a boot and flashing from the start. We set them before the mechanical contractor cuts the roof, so the cut has a detail.