Flat Roof Flashing Leak Specialists

More than half of all flat roof leaks in Brooklyn start at flashing-those metal and membrane transitions where your roof meets walls, parapets, chimneys, or skylights-not in the open field of the roof itself. That’s why you can patch a blister or bubble three times and still see water at the same ceiling corner every spring storm. The real culprit lives along the edges and vertical transitions, and fixing it requires precision metalwork and waterproofing knowledge most general roofers don’t specialize in.

I’m Eli Mandel, and for 24 years I’ve focused almost exclusively on flat roof details that other contractors rush through. I started in commercial roofing in Manhattan, fell in love with sheet metal and flashing work, then brought that precision back to Brooklyn brownstones, walk-ups, and mixed-use buildings. Most of my calls come from property owners who’ve hired two or three roofers already-each one smeared more tar around a parapet or skylight, claimed the leak was “fixed,” and left behind the same problem six months later.

Tired of Chasing the Same Flat Roof Leak at the Edge or Wall?

You see it on the top-floor ceiling, right where the wall meets the roof line. A brown stain. Bubbling paint. Maybe damp drywall after heavy rain. Someone comes out, slaps some roof cement around the parapet base, and tells you it’s sealed. Three months later, the stain is back.

That cycle repeats because the repair never addressed the actual flashing system-the layered assembly of membrane, metal, fasteners, and sealants that has to flex with your building, shed gallons of water per storm, and survive Brooklyn’s freeze-thaw punishment. When any part of that system fails, water finds the gap.

You’re probably dealing with a flat roof flashing leak if:

• Leaks show up near walls, roof edges, or around penetrations like chimneys and skylights-not in the middle of the roof.
• The same leak returns after one or more “repairs,” usually in wet or windy weather.
• You can see metal flashing that’s rusted, bent away from the wall, or buried under layers of black goop.
• Interior damage appears at ceiling corners, along the top of walls, or near window frames on upper floors.

What Flat Roof Flashing Actually Does (In Plain English)

Flashing is the transition material-metal, membrane, or both-that bridges your flat roof surface to any vertical element: parapets, side walls, chimneys, bulkheads, skylights, vents, HVAC curbs. Think of it as a custom-fit gasket for every place the roof stops being horizontal. Water can’t just run off a flat roof like it does on a pitched one; it pools, backs up behind ice dams, and tests every seam. Flashing is what keeps those seams watertight.

On Brooklyn flat roofs, flashing lives in high-stress zones. Brick parapets shift as mortar ages. Metal expands and contracts with temperature swings. Membrane shrinks over time. If the flashing wasn’t installed to accommodate all that movement-or if someone shortcuts it during a roof overlay-you get separation, cracking, or rust-through, and water sneaks in.

Where you’ll find flashing on a typical Brooklyn flat roof:

• Along parapet walls and coping caps at roof perimeters.
• Around chimneys, vent stacks, skylights, and roof hatches.
• At inside and outside corners where walls meet the roof.
• Around rooftop HVAC equipment curbs and supports.
• At roof edge terminations and drip edges.

Why flashing is where most leaks start: The open field of your roof-modified bitumen, EPDM, TPO, or built-up layers-usually performs fine if it was installed correctly. Leaks begin where that membrane has to turn up a wall, wrap a corner, or tie into metal, because those details require multiple materials working together. Miss one step-skip the primer, use incompatible sealant, leave gaps in the metal-and you’ve created a leak path that no amount of roof cement will permanently close.

Is It Really a Flashing Leak? Quick Symptom Map

Most people call me after they’ve already spent money on a “roof repair” that didn’t work. Walk through your building and map where you see water damage inside, then think about what’s directly above or adjacent on the roof. If the pattern matches these scenarios, flashing is almost certainly your issue:

If you recognize your situation in that table, the next storm will likely test the same weak flashing detail again. Temporary sealant might buy you a few months, but the underlying problem-poor installation, material failure, or building movement-remains.

Why Flat Roof Flashing Fails Faster in Brooklyn

Brooklyn’s building stock and weather create a perfect storm for flashing failure. You’ve got century-old masonry buildings with parapets that have settled and cracked. You’ve got multiple roof overlays stacked on top of each other, each one trying to tie into flashing that was marginal to begin with. And you’ve got harsh seasonal swings-summer heat that bakes metal and membrane, winter ice that pries open every gap, and coastal wind-driven rain that hammers exposed edges.

Stress points we see constantly on Brooklyn flat roofs:

• Parapet walls with deteriorated mortar joints behind the base flashing, letting water wick into the brick and travel down inside the wall.
• Layered roofing systems where a contractor added new membrane but reused old, corroded metal flashing or skipped proper tie-ins.
• Ice dams along parapet bases and in inside corners, where melt-freeze cycles push water under metal caps and sealants.
• Wind uplift at roof edges and copings, especially on buildings near the water, that pulls fasteners loose and opens flashing seams.
• Thermal expansion differences between metal flashing and membrane, causing separation at lap seams and terminations.

I’ve opened up dozens of “mysterious” leaks in Park Slope, Crown Heights, and Williamsburg where the roof membrane itself looked fine-no punctures, decent thickness-but the flashing at the parapet was a mess of rusted sheet metal, dried-out mastic, and gaps you could slide a credit card through.

Top Causes of Flat Roof Flashing Leaks

After two decades of fixing what other roofers left behind, I can usually predict what I’ll find before I even climb the ladder. These are the recurring failures:

1. Flashing installed wrong from day one. Membrane not turned up high enough, metal cut too short, no reinforcing fabric at corners, incompatible materials, or skipped fasteners. The roof leaks within a year, and every patch just postpones the inevitable rebuild.
2. Shortcut re-roofs that ignored old flashing. Contractor rolls out new membrane over the field but leaves decade-old, failing base and edge flashing in place, claiming it’s “still good.” It’s not. New roof, same leaks.
3. Dried, cracked, or missing sealants. Sealant is a maintenance item, not a permanent fix. When it’s used as the primary waterproofing instead of as a backup to proper flashing, it fails fast-especially on south- and west-facing walls.
4. Building movement pulling flashing loose. Brick buildings settle. Wood framing expands and contracts. If the flashing system is too rigid or poorly fastened, that movement creates gaps and tears.
5. Rusted or corroded metal flashing. Galvanized steel rusts through at edges and fastener holes. Aluminum corrodes where it contacts certain masonry or roofing materials. Once the metal fails, no amount of coating will restore its function.
6. DIY tar layers over the real problem. I’ve peeled back six or eight layers of roof cement, each one applied by a different handyman or roofer, to find that the original flashing detail underneath was never actually built correctly. All that tar just hid the issue and made future repairs harder.

What a Flat Roof Flashing Leak Specialist Does Differently

Most general roofers are great at laying down membrane in the open field. That’s production work-roll it out, torch or glue it, move on. Flashing is different. It’s custom fabrication, material compatibility, understanding building movement, knowing which sealant works with which substrate, and having the patience to rebuild a corner detail three times until it’s right.

When someone calls me for a flashing leak, I’m not looking to sell them a whole new roof unless they actually need it. I’m there to solve the leak at its source, which usually means opening up a section of flashing, seeing how water is really traveling, and rebuilding that transition so the roof and wall work as a system.

Typical “patch” approach (what doesn’t work long-term):

• Smear roof cement or mastic over a visible gap or rust spot.
• Bury failing metal under layers of sealant without removing or replacing it.
• Ignore cracks in the parapet, wall movement, or deteriorated mortar.
• Treat only the exact spot where water dripped, not the whole flashing line.

Specialist flashing approach (what we actually do):

• Carefully open the suspect area to see the full flashing assembly-membrane layers, metal, fasteners, substrate condition.
• Assess the wall or curb itself-mortar joints, masonry integrity, wood rot, structural movement.
• Rebuild the flashing detail step by step: proper substrate prep, compatible primer, correct membrane turn-up height, new metal with expansion provisions, fasteners in the right locations, and sealant only where it’s meant to serve as a secondary barrier.
• Test the repair visually and, when needed, with controlled water to confirm the path is sealed.

The difference in longevity is dramatic. A tar patch might last through one winter. A properly rebuilt flashing detail should give you ten to twenty years, depending on the materials and how well the rest of the roof is maintained.

Our Flat Roof Flashing Leak Inspection Process in Brooklyn

When you call me for a flashing leak, the inspection follows a methodical sequence. I want to understand the whole story-where water shows up inside, how it’s traveling through the building envelope, what’s failing on the roof, and why it failed-so I can give you a real solution, not a guess.

Step 1: Interior Leak Mapping. We start inside your building, documenting exactly where you see stains, dampness, or active dripping. I ask when leaks happen-during heavy rain, after snow melt, with wind from a particular direction-because that tells me a lot about whether we’re dealing with a drainage issue, a wind-driven rain problem, or ice damming.

Step 2: Roof-Level Survey. On the roof, I walk every flashing line: all parapet walls, around every penetration (chimneys, vents, skylights, hatches, HVAC curbs), and along edge terminations. I’m looking for obvious failures-separated metal, open seams, missing fasteners, rust-through, cracked membrane-and also for subtle clues like ponding water near a flashing line, which suggests a drainage problem that’s overwhelming the detail.

Step 3: Detail Investigation. If the failure isn’t obvious from the surface, I’ll gently open a section of flashing-lift a metal cap, peel back membrane-to see what’s underneath. That’s where I usually find the smoking gun: no primer on the masonry, membrane that was never actually adhered to the wall, missing or corroded fasteners, incompatible materials reacting with each other.

Step 4: Photo Documentation and Explanation. I take close-up photos of every problem area and, just as importantly, photos that show you what a correct detail should look like. Then I walk you through what I found in plain language: “This inside corner has no reinforcing fabric, so the membrane tore when the building settled,” or “Your edge metal is only fastened every two feet and it should be every six inches, so wind is lifting it and breaking the seal.”

Step 5: Repair Options and Priorities. Not every flashing line needs immediate work. I’ll tell you what must be fixed now to stop active leaks, what should be addressed soon before it becomes a leak, and what can wait. If you have failing flashing in multiple areas and the rest of the roof is also near end-of-life, I’ll give you the cost-benefit analysis of doing a comprehensive flashing overhaul now versus planning for a full roof replacement in a year or two and addressing only emergency leaks in the meantime.

Flat Roof Flashing Repair and Replacement Options

Flashing work isn’t one-size-fits-all. The right scope depends on how much of the system is failing, the condition of the main roof, and your timeline and budget.

Localized Flashing Repair: Best when you have one or two specific leak points-say, a corner where the membrane has pulled away, or a chimney with deteriorated counter-flashing-and the rest of the roof and flashing system is sound. We remove and rebuild just that section, tying it correctly into the existing membrane and metal. Cost is modest, downtime is minimal, and if the diagnosis is right, the leak stops permanently. I did this on a Park Slope brownstone last year where the leak was isolated to a single inside corner at the rear parapet; rebuilt that one detail, and the owner hasn’t seen water since.

Sectional Flashing Upgrade: Makes sense when you have multiple leaks along one wall, around a cluster of penetrations, or across an entire edge of the building. Instead of playing whack-a-mole with individual spots, we address the whole zone-replace or upgrade the base flashing, install new metal caps, reinforce corners, ensure proper drainage. This approach works well on buildings where one side takes more weather punishment (west-facing walls catching wind-driven rain, for example) or where an addition created a complex flashing transition that was never detailed correctly.

Full Perimeter or System Flashing Overhaul: If your flat roof is ten-plus years old and you’re seeing flashing failures in several locations, it often makes financial sense to redo all the perimeter and penetration flashing at once, especially if you’re planning to keep the existing membrane for another five to ten years. We systematically replace base flashings, edge metal, copings, and penetration flashings around the entire roof. It’s a bigger investment up front, but you eliminate the cycle of repair calls and you maximize the remaining life of your roof system.

Materials and Techniques We Rely On for Durable Flashing

I’m not brand-loyal, but I am material-science obsessive. Every flashing job is a combination of compatible materials that have to move together, shed water together, and survive UV, temperature swings, and physical abuse together. Get one material wrong and the whole assembly fails.

Typical components in a quality flat roof flashing detail:

• Base flashing: Usually the same membrane material as your main roof-modified bitumen, EPDM, TPO-turned up the wall or curb at least eight inches (code minimum in most cases, but I often go higher if drainage or wall condition warrants it).
• Reinforcing fabric or strip: At inside and outside corners, and anywhere the membrane changes direction sharply, we embed reinforcing fabric in mastic or adhesive to prevent tearing.
• Metal flashing and caps: Aluminum, galvanized steel, or coated steel, depending on the building and exposure. Metal sheds water away from the wall, protects the membrane from UV, and provides a finished edge. Proper metal flashing is fastened at regular intervals and detailed with expansion joints on long runs to accommodate thermal movement.
• Counter-flashing: Where the wall is masonry, we often install counter-flashing that’s set into a mortar joint or reglet (a kerf cut into the brick), so it overlaps the base flashing and prevents water from sneaking behind the metal.
• Sealants: High-grade polyurethane or silicone sealants, but only where they’re meant to serve as a secondary seal-at metal laps, terminations, and fastener heads. Sealant is not the primary waterproofing; the membrane and metal are.

Adapting to your existing roof system: If your roof is modified bitumen, I use torch-grade modified for the flashing and heat-weld it in place. If it’s EPDM or TPO, I use compatible primers, adhesives, and tape systems per the manufacturer’s specs. If you’ve got an older built-up roof with gravel, I often recommend transitioning to a modern membrane flashing detail when we rebuild, because it performs better and is easier to inspect and maintain going forward.

One thing I will not do: mix incompatible materials to save a few bucks. I’ve seen TPO flashing over modified bitumen roofs with no separation layer, EPDM glued with the wrong adhesive, aluminum flashing in direct contact with wet mortar (which corrodes the aluminum), and torch-grade membrane applied over wood without proper clearance. Every one of those shortcuts creates a leak within months. If a material incompatibility exists, I’ll either spec a separation layer or choose a different approach entirely.

What Affects the Cost and Timeline of Flashing Leak Repairs?

Owners always want a ballpark number before I even see the roof, which I understand. But flashing work has too many variables for a blind quote. Here’s what drives cost and schedule:

• Length and complexity of the flashing run. A simple 10-foot section of wall flashing is a half-day job. A full building perimeter with multiple corners, elevation changes, and transitions can take several days.
• Height and access. Ground-level flat roofs are easy. Four-story walk-ups with no interior roof access mean ladders or scaffolding. Buildings with sidewalk sheds, storefront awnings, or adjacent properties require careful planning and sometimes permits.
• Condition of the substrate. If I open up flashing and find rotted wood, crumbling masonry, or rusted steel framing, we have to address that before we can install new flashing. I’ve had jobs where “simple flashing repair” turned into parapet rebuilds because the brick had deteriorated so badly the flashing had nothing sound to fasten to.
• Type and age of the existing roof. Tying new flashing into a five-year-old membrane is straightforward. Tying into a 20-year-old roof with three overlays and uncertain adhesion requires more care, testing, and sometimes custom details to ensure a watertight bond.
• Number of separate leak locations. If you have ten penetrations that all need flashing work, the job costs less per penetration than if we mobilize for a single skylight repair, but total cost and time go up.

A localized flashing repair on an accessible Brooklyn rowhouse might run $800 to $2,200 depending on scope. A sectional upgrade along one parapet wall typically falls in the $2,500 to $6,000 range. A comprehensive perimeter flashing overhaul on a small apartment building can run $8,000 to $18,000 or more if masonry work and access logistics are involved. I always provide a written scope and cost breakdown after the inspection so there are no surprises.

Timeline: Straightforward repairs usually wrap up in one to three days, weather permitting. Larger projects might take a week or more, and if we need scaffolding or have to coordinate with other trades (masons, carpenters), add time for scheduling and permits.

Talk to a Flat Roof Flashing Leak Specialist in Brooklyn

If you’ve been chasing the same leak for months or years, or if you’ve had three roofers tell you three different things, you need someone who specializes in the problem, not someone who treats flashing as an afterthought. Most flat roof leaks trace back to failed or poorly installed flashing at walls, edges, and penetrations, and fixing them correctly requires a different skill set than rolling out membrane in the field.

I’m Eli Mandel with FlatTop Brooklyn, and I’ve spent 24 years focusing on the details that stop flat roof leaks for good. When you call, you get a methodical inspection, clear photo documentation, honest explanations of what’s wrong and why, and repair options that fit your building and budget. No upselling, no mystery leaks, no Band-Aids.

When you contact FlatTop Brooklyn for a flat roof flashing leak assessment, you get:

• A focused inspection of your flashing lines, parapets, edges, and penetrations.
• Photos and plain-language explanations of what’s failing and how water is getting in.
• Repair or replacement options tailored to your Brooklyn building, with realistic cost and timeline estimates.
• Work done right the first time, so you’re not calling someone else in six months.

Don’t let the next rainstorm test those same weak flashing details again. Call us for a flat roof flashing leak inspection in Brooklyn, and let’s finally solve the problem at its source.