Flashing Failure Repair in the Bronx, NY

The bulkhead base is where a pre-war six-story apartment house in Belmont fails first, before anywhere else on the roof. The bulkhead is the small structure over the stairs, and the flashing where its wall meets the roof is a long vertical joint that takes water, sun and movement every day. A property manager who gets a top-floor complaint should check that base flashing first, then the parapet, then every pipe and curb.

Flashing is the strip of material that turns the roof surface up a wall, around a pipe or over a curb, and finishes under a cap that sheds water over the top. When it fails, the field of the roof can be perfectly sound and the building still leaks. On Bronx, NY roofs the repair means cutting back to sound material and rebuilding the detail, and no bead of sealant is allowed to stand.

Pre-War Apartment Houses

Belmont is dominated by five and six story apartment buildings, both walk-up and lift-served, mostly built before 1939, with Art Deco and Tudor style apartment buildings and row houses. Longwood, Tremont and Bedford Park share that stock, while Concourse adds Tudor Revival to Art Deco blocks from the era of the 1901 Tenement House Act. A roof on one of these has a tall parapet, a bulkhead, vent stacks and a drain or two, and each is a flashing detail.

The first walk covers them in order: bulkhead base, parapet counterflashing, stack boots, drain flange, then rooftop equipment curbs. We press and pull each, look for gaps between the sheet and the brick, and mark cracked sealant, lifted metal and open mortar above the termination.

Belmont also carries commercial life on its ground floors. Belmont's main street is Arthur Avenue, East 187th Street is crowded with delis, bakeries and cafes, and the Arthur Avenue Retail Market takes up a whole block between Arthur and Belmont Avenues. Food businesses mean exhaust fans, and exhaust fans mean curb flashing that sees heat and grease, so a roof over a kitchen or bakery gets its fan curbs checked first.

Why Flashing Fails

Four reasons cover most failures. Movement: the roof and the wall expand and shrink at different rates, so the joint works open over many seasons. Age: tar and sealant harden and crack in sun. Water behind the top edge: a cracked mortar joint above the termination lets water run behind the flashing and push it off the wall. And added items: every vent, fan and sign mount somebody added later is a hole that was probably not flashed properly.

A Bronx roof sees a wide thermal range, with Central Park averaging 95.7 F in July and dropping to -15 F. A stiff strip of flashing at a wall takes the full swing, and it fails first. Add the freeze-thaw of a winter with about 29.8 inches of snow a year at Central Park, and any hairline crack takes in water that expands as it freezes.

Superintendents often see the early warning. A damp patch under the cornice, a white crust on the brick below the parapet or a stain that returns after painting all point to water entering at the roof edge. The crust is efflorescence, salt carried out of the masonry by moving water. It does not hurt the wall by itself, but it shows where water is travelling, and the flashing above it is the first place to look.

Historic Districts and Exterior Work

Much of Concourse became the Grand Concourse Historic District in 2011 under the Landmarks Preservation Commission, and exterior work such as roof replacement can fall under its review. The Mott Haven Historic District along Alexander Avenue between East 138th and East 141st Streets is mainly four and five story row houses from the late 19th century and was listed on the National Register of Historic Places in 1980. If a building sits in one of those districts, confirm what the exterior work needs before the scope is written.

Parapet caps, cornices and visible coping are the items most likely to draw review. Visible and hidden items are scoped separately, so membrane and flashing behind the parapet can start while approval for street-facing pieces proceeds. A Concourse building with a failed cap is a candidate for that split.

How We Find the Opening

We test with a hose, one detail at a time, starting at the lowest point and working up while someone watches the ceiling below. That keeps us from replacing a sound flashing while the real opening sits a few feet away. It is the same method used in commercial roof leak repair, and it works because water usually enters at one place and shows up at another.

Failures cluster. Where one flashing has opened, its neighbors on the same wall are suspect, since the same conditions run along the whole line. When we find one, we walk the whole wall and probe every joint, and we check the neighbors: a wind-lifted edge and a split seam are common companions.

Hoses are used carefully on an occupied building. We protect the roof hatch and stair, keep water off equipment, and watch the interior for the first drip. A test run in sections gives a clean answer in an hour or two, and the answer is photographed with a note of which section produced the leak.

The Repair

Repair starts by cutting the old flashing back to sound material and cleaning and priming the wall. New base flashing is set and welded or adhered to the field membrane, and a new counterflashing or termination bar is fastened and sealed at the top. On masonry, a mason repoints the joint above first, because flashing cannot hold on a crumbling wall. Around penetrations, a formed boot replaces the bead of sealant. Equipment curbs get new base flashing and caps, and the skylight and penetration flashing work follows the same steps. Cost follows the length of flashing, wall height, masonry condition, penetrations and access. A failed flashing admits water every rain, so waiting costs more than fixing.

Timing follows temperature. Sealants and adhesives need a minimum temperature to cure, so the best months for flashing work are spring and fall. In winter we make a mechanical temporary seal and schedule the permanent rebuild for milder weather. On an occupied building the work moves in sections along the wall, and each section is closed watertight before the crew leaves.

Commercial Roofing Questions

Can flashing be fixed with roof cement?

Roof cement is a temporary measure. It cracks with the next temperature swing and hides the problem. A lasting repair rebuilds the flashing with new material tied into the membrane and fastened at the top.

How high should base flashing run up a wall?

Typically at least eight inches above the roof surface, and higher where snow or ponding is likely. The membrane maker's detail and the code set the height, and we follow the stricter one.

Do we need a mason before the roofer?

If the wall above the flashing has open mortar or loose brick, yes. A flashing on a failing wall fails again, so repointing comes first and we coordinate the order.

Why does my top-floor unit leak only in wind-driven rain?

Wind pushes rain sideways into joints that shed vertical rain fine. A counterflashing with a small gap, or a cracked reglet, leaks from one direction only. A hose test from that side usually reproduces it.

What should I send to start?

A photo of the bulkhead base and the parapet, with the roof age and the last tenant complaint, gets the walk booked.