A pre-war apartment building in the Grand Concourse Historic District is a parapet wall with a roof behind it, and the details at the wall decide whether the roof stays dry. A manager should check what the exterior work needs from the Landmarks Preservation Commission before a scope is written. Soprema is a roofing and waterproofing manufacturer known for modified bitumen membranes, liquid-applied flashing resins and insulation. We install and repair those system categories on Bronx buildings, and the old masonry of the borough is where they earn their keep.
Modified Bitumen on Pre-War Roofs
Modified bitumen is asphalt blended with polymers and reinforced with polyester or fiberglass mats. It comes in rolls with a base sheet and a cap sheet, laid in two plies. The plies can be heat-welded with a torch, mopped with hot asphalt, applied with cold adhesive or self-adhered with a sticky back. The cap sheet carries granules that shed sun and protect the asphalt.
It is forgiving on roofs with many details, which describes most pre-war roofs: bulkheads, stair hatches, plumbing vents, short parapet runs and odd corners. The layered build can be patched and tied into, and a second ply gives a margin for foot traffic. For buildings like these, modified bitumen is often the first system we consider.
Failure modes are specific. Laps that were not fully sealed open first, usually at the low side where water runs. Granule loss exposes the asphalt to sun, and the cap sheet cracks along the grain after a few hard winters. Where two plies were laid with bunched felts or air pockets, blisters form and burst. We probe laps, look for bare patches and press on blisters before we decide between repair and replacement.
Historic Districts and Exterior Work
Concourse offers five and six story multifamily blocks in Tudor Revival to Art Deco styles, built under the 1901 Tenement House Act. In 2011 the Landmarks Preservation Commission made much of the neighborhood the Grand Concourse Historic District, so exterior work such as roof replacement can fall under its review. Along Alexander Avenue, the Mott Haven Historic District is mostly four and five story row houses built in the late 1800s.
For a roof in a district like Concourse or Mott Haven, the question is what the review covers: visible parapet caps, cornices, skylights or rooftop additions. The flat roof behind a parapet may not be visible, but the edge usually is. We confirm status early and build review time into the schedule.
Owners sometimes assume a historic district bans modern roofing. It does not. It governs what is visible and how it looks. The Department of Buildings distributes the 2022 NYC Construction Codes. Permits come from there. We sort the scope into those two piles at the start.
Liquid-Applied Flashing Resins
Old masonry parapets are uneven. The brick face is rough, the corners are not square and the coping joints are irregular. A sheet flashing struggles with that surface. A liquid-applied flashing resin, reinforced with fabric and applied wet, flows into the irregularities and cures into a continuous layer. It is useful at parapet bases, around pipe clusters and at odd corners.
Soprema is one source of such resins, including Alsan, a liquid flashing system. We use liquid flashing where it fits the detail, check compatibility with the main membrane and confirm cure conditions, since temperature and humidity change cure time. A resin that gets rained on before it cures is a failed flashing.
Surface preparation is the whole job. The substrate must be clean, dry and primed, and the fabric must be fully embedded with no dry spots. We check coverage with a wet-film gauge during application and measure cured thickness afterward.
Parapet Walls, Counterflashing and Coping
On a five story walk-up, most leaks begin where the roof meets the wall. Coping loosens, counterflashing lets go and water travels down the inside of the wall to a top-floor ceiling. A new membrane fixes nothing if it ends against a bad wall. We repoint soft joints, reset coping, install new counterflashing in a cut reglet and then tie the membrane into the new detail.
The work is done in order: masonry first, flashing second, membrane third. Each step is photographed. A coping and edge metal repair is included in the scope when the wall needs it, because a roof is only as dry as its edge.
Insulation and Assembly
Under the membrane, rigid insulation builds the thermal layer and the slope. On older roofs with little or none, new insulation can raise the roof at doors and parapets, so the available height decides the thickness. We measure at every threshold and parapet before we specify. Tapered boards correct ponding and send water to the drains.
A cover board over the insulation protects it from hot work and foot traffic. If a torch is used, the substrate has to be non-combustible or protected, and fire watch rules apply. Where torch work is a concern, we use cold-applied or self-adhered plies instead.
Drains deserve a second look when insulation changes. Raising the roof surface by a couple of inches puts the drain bowl below the new surface unless the bowl is raised too, and an unraised bowl becomes a pond. We reset drain bodies, replace clamping rings and extend leaders so the new roof drains as designed.
How We Install and Document
We install to the manufacturer's published requirements: substrate preparation, ply layout, laps, flashing heights and terminations. We photograph each step and log weather and materials. Whether a warranty is available depends on the manufacturer's program, and the scope-writing stage is when the terms are laid out. Our warranty management work keeps the paperwork in order once the job ends.
Ida's record hour of 3.15 inches in September 2021 is why drains are reviewed and overflow is added where a roof has none.
Cost, Timing and Code
Price follows roof area, tear-off, insulation, the amount of masonry and flashing work, access and any review time in a historic district. The Department of Buildings, which publishes the 2022 NYC Construction Codes, answers filing questions. With the Central Park station averaging 95.7 F in July and reaching -15 F, material temperature windows shape the schedule. We compare with other makers, such as GAF and Johns Manville, when owners ask.
Commercial Roofing Questions
Does a historic district stop me from replacing a flat roof?
It does not stop it, but it can add review for visible exterior parts. We confirm which parts are reviewed and when to file, so the schedule includes the time.
Is torch-applied modified bitumen safe on an old building?
It can be, with the right substrate protection, fire watch and training. Where wood or foam is close to the work, we choose cold-applied or self-adhered plies instead.
How long does liquid flashing take to cure?
It varies with temperature and humidity, from hours to a day. We schedule it for dry weather and protect it until cured. Rain on uncured resin ruins the detail.
Why repoint the parapet before roofing?
Because the flashing ties into the wall. Soft mortar or loose brick cannot hold a termination, and water will find the gap. Repair the wall first and the roof detail lasts.
Can modified bitumen go over my existing roof?
If the existing roof is dry, sound and within building limits, a recover is possible. We scan and core first, then say whether a recover or tear-off is right.
Send the Address, Roof Age and Last Work Order
Tell us the building type, the roof age and the last tenant complaint, and ask for a flat-roof walk before anyone writes a scope. If the building is in a historic district, say so.
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