Sealing the upstands, copings and party-wall terminations where a Philadelphia rowhouse membrane meets masonry.
Fastest: call (833) 751-2102. Or send this and we call you back.
Parapet and cornice flashing is the detail where a low-slope roof turns up and stops against masonry. On Philadelphia rowhouses it is the joint that most often lets water past, and on an attached house it is shared with the neighbours. Philadelphia Roofing sends a local roofer to open, rebuild and seal that termination.
Walk a row of brick houses and look at the roofline. The front wall carries on above the roof as a parapet, often finished with a cornice that projects over the street. Behind it the roof membrane turns up the inside face of that wall and is sealed near the top. Nothing else on the roof has to do so many jobs at once.
Contractor and inspector guidance for this housing type names the same three culprits over and over: parapet flashing, drain and scupper seams, and ponding water. The first of those is this page. It is unglamorous work and it is where a surprising share of top-floor water stains begin.
The consequence on an attached house is particular. Where a membrane terminates against a party-wall parapet, the seal has to stop water migrating into the next house along, which means the repair is only finished when both sides of the wall are right.
A parapet is not a safety barrier. It is a low wall that can be loose at the top, and leaning on it or standing on it to look over the street edge is how people fall. Do not try to lift coping stones, probe mortar from a ladder set against the wall, or work on a cornice from a window. Loose masonry above a pavement is also a hazard to people below, so if bricks or coping look ready to come down, keep the pavement clear and call (833) 751-2102 rather than attempting to secure it yourself.
The street-facing detail, and the one a historic district cares about. A projecting cornice adds a horizontal surface and a joint behind it, and its condition is usually visible from the pavement, which makes it the easiest part of a roof for an owner to monitor.
The wall shared with the house next door, often with roofs at slightly different levels on either side. The membrane turns up both faces and the seal has to be continuous, because water in the head of a shared wall will reach whichever side has the weaker detail.
At the back of many rowhouses the water runs to a gutter along the wall rather than to an internal drain. That makes the rear termination both a flashing detail and part of the drainage, and the two have to be solved together rather than in turn.
If it's an emergency, call now. For non-urgent parapet and cornice flashing, send the form and we'll call you back.
Because it is exposed on every surface and it is a joint between materials that behave differently. Brick absorbs water, membrane does not; masonry and sheet expand at different rates in sun. The termination at the top of the upstand has to stay watertight while the two sides of it keep moving.
Add the geometry. A parapet stands proud of the roof, so wind-driven rain reaches its street face, its top and its inside face, and nothing above it is shedding water away. On a tall narrow house the wall also takes the weather from the open side of the block.
Then consider what is behind the flashing. Older brickwork with lime or softened mortar will take water in through open joints and carry it down inside the wall, emerging well below where it entered. That is why this repair often starts with pointing rather than with sheet material, and why a flashing job that ignores the masonry comes back.
It can be. The Philadelphia Historical Commission's roofs guidance favours work that is inconspicuous from the public right-of-way, and a cornice is about as conspicuous as a roof detail gets. Flat roofs hidden behind a parapet are generally treated more simply. The Commission confirms what applies to an address.
The practical reading is that what the street can see attracts attention and what it cannot usually does not. A membrane termination behind a parapet is one thing; altering the profile, material or paint line of a projecting cornice on a designated building is another, and that can need review before L&I issues a permit.
So the order of operations matters on a designated property. Confirm the status for the address, establish whether the work will be visible from the public right-of-way, and get the review question settled before the detail is specified. Our guide on slate and historic roofs in Philadelphia covers how that process tends to run.
Water collects in the head of a wall that belongs to two households and comes out wherever the plaster is weakest, which may be next door. Contractor guidance for this roof type treats sealing the party-wall membrane termination as mandatory rather than optional for exactly that reason.
It also makes diagnosis confusing. A neighbour with a wet top-floor ceiling may have a sound roof and a leak that originated two doors down, and each owner can get a different roofer with a different theory. Opening the shared detail and looking at it is what ends the argument.
The repair itself is straightforward once agreed: a continuous upstand on each side, held and capped, with the coping made good above it. Getting agreement is the slow part, so tell the adjoining owners early. In the dense blocks of Queen Village and Bella Vista and Northern Liberties a crew may need to cross a neighbouring roof just to reach the wall.
Usually yes, if the membrane in the open field is sound and the deck beneath it is dry. The termination is a defined length of work. What changes the answer is wet insulation or a membrane that has reached the end of its service, in which case flashing alone is a poor investment.
A roofer should tell you which of those two situations you are in and show you why: a probe, a lifted corner, a photograph of the deck. Rebuilding a perfect upstand against a sheet that is splitting elsewhere is work you will pay for twice.
Where the membrane is fine, this is one of the better value repairs on a rowhouse, because it addresses the detail that fails first. If the roof is coming to the end of its life anyway, the flashing is designed in as part of a flat roof replacement rather than done twice.
The roofer looks at the inside of the parapet from the roof and at the street face from ground level or a ladder. Water entering the top of a wall can show itself a storey below on the opposite face, so a single viewpoint is not enough.
The top of the wall is the most exposed masonry on the building. A cracked coping, an open joint or a cap with no fall sends water straight into the core of the wall, where no amount of membrane work on the inside face will catch it.
The old flashing, bar and sealant come off so the roofer can see the true condition of the upstand, the masonry behind it and how high the membrane was actually taken. A termination finished too low is a common find on earlier repairs.
Flashing bonds to sound material or it does not bond at all. Open joints are repointed and spalled brick faces made good before any new membrane or counterflashing goes on, which is why this job sometimes includes a little masonry work.
The membrane upstand is taken to a proper height, mechanically held and capped with counterflashing or a sealed head joint so water cannot get behind it. Party-wall terminations are sealed along their whole length rather than only where the stain appeared.
Parapets are a brick-city feature, and this is a brick city. The continuous rows of Center City, South Philadelphia and Fishtown present a near-unbroken line of shared walls standing above roof level, each one a termination for two membranes.
Wind is the local load that finds a weak upstand. The National Weather Service's review of Tropical Storm Isaias on 4 August 2020 lists eight confirmed tornadoes in the region, including EF2 tornadoes in Philadelphia and Bucks County, alongside widespread tropical-storm-force gusts. A flashing edge that is only held by old sealant is what lifts first in that kind of wind.
Older blocks make the masonry part larger. With roughly four in ten city homes dating from before 1940 by an older Census-based analysis, a flashing call here frequently turns into pointing the top courses of a wall that has not been touched in decades, particularly in Old City and Society Hill and Germantown.
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Repairs to flat and very low-slope membrane roofs on Philadelphia rowhouses, twins and converted buildings, starting at the drainage path.
Clearing, resealing and re-detailing the outlets that take water off a low-slope rowhouse roof.
Replacing the roof on an attached house, where the party walls, the neighbours and the street are as much of the job as the covering.
Repairing the flashing, counterflashing and masonry where a chimney or party-wall stack passes through a roof.
Most Philadelphia rowhouse roofs look flat but slope toward a drain, with a minimum fall of a quarter inch for every foot.
Tropical Storm Isaias crossed the Philadelphia area on 4 August 2020.
Base flashing is the part that turns up from the roof against the wall. Counterflashing is the piece above it, let into or fixed to the masonry, that caps the top edge so water cannot run behind. A termination needs both working together.
Only if it has failed. A cracked, tilted or open-jointed cap lets water into the core of the wall above every flashing you fit, so it gets checked first. Sound coping with tight joints can often just be repointed.
Very often, especially when the damp sits high on an outside wall and shows up after driving rain rather than after every shower. A roof leak tends to appear away from the wall line; a parapet leak hugs it.
Sometimes, when the entry point was an open mortar joint and the membrane termination is still sound. More often pointing and flashing are both part of the fix, because water has already found more than one route into the head of the wall.
Usually from the roof itself, working back toward the wall, with access planned around the kerb. Tall narrow houses with no setback leave very little room for a ladder on the street side, which is one reason this work is quoted after a look rather than over the phone.
The waterproofing principle is the same but the substrate is not. A cornice with timber members needs the rot assessed before anything is sealed over it, and on a designated building its appearance from the street may be reviewable. That is scoped on site.