Stop Flat Roof Chimney Leak Problems
Water Coming In Around Your Chimney on a Flat Roof?
You’ve got a drip on your ceiling. It’s coming from right below the chimney. Again. Maybe you paid someone to tar around it six months ago. Didn’t work. Now you’re wondering if the whole roof needs replacement, or if the chimney’s falling apart, or both-and every forecast makes you tense up.
If you’ve got this situation right now:
- Flat roof. Brick or block chimney.
- Leaks or stains near the chimney chase or wall.
- Patches or tar blobs that didn’t solve it for long.
You’re not alone, and you’re not crazy. Flat roof chimney leaks are the most misdiagnosed and poorly fixed problem I see in Brooklyn-because water can sneak in from six different angles, and most quick fixes only address one. The rest of this page walks you through what’s actually happening up there, why tar keeps failing, and what a proper chimney leak repair looks like on a Brooklyn flat roof.
First Things to Do When You Spot a Chimney Leak
Before the next storm:
- Move furniture, electronics, or valuables away from the leak area inside.
- Put a container or plastic sheeting where water is dripping.
- Take clear photos of the leak inside and the chimney/roof area outside, if it’s safe to do so.
- Avoid climbing on a wet flat roof; wait for it to dry or let a pro inspect.
Warning: Smearing more tar around the chimney without understanding the cause can trap water inside brick joints or under the roof membrane, hide damage, and make later repairs more expensive. On a flat roof in winter, that tar will crack and shrink, opening new gaps within a season.
Why Flat Roofs and Chimneys in Brooklyn Leak So Often
Brooklyn’s full of row houses, brownstones, and small apartment buildings built eighty to a hundred years ago. Most have flat roofs with brick chimneys flashed by a tin smith in 1940, then re-roofed four times since, each time burying the old flashing under a new layer. Every winter freeze-thaw cycle lifts the bricks a fraction. Every summer, thermal expansion works the metal. Every decade, another layer of modified bitumen or rubber goes down-often without properly addressing the chimney intersection.
Here’s what makes it worse:
| Weather Stress | Building Reality |
|---|---|
| Heavy rains that pond on flat roofs | Older chimneys with cracked mortar joints |
| Snow and ice sitting against chimney bases | Multiple re-roofs with flashing buried under new layers |
| Temperature swings that expand and contract metal flashing and brick | DIY tar patches that temporarily hide problems |
On a Bedford-Stuyvesant building last year, I found three separate layers of step flashing around one chimney, each installed without removing the failed one underneath. Water was traveling sideways between the layers, then dropping through a gap in the wood deck. The homeowner had paid three different roofers over five years. None had pulled the assembly apart to see what was really going on.
How Water Actually Sneaks In Around a Chimney on a Flat Roof
Typical leak paths we see:
- Failed base flashing where the flat roof membrane meets the vertical chimney.
- Missing or loose counter-flashing embedded into the brick joints.
- Cracked mortar joints or bricks that absorb and channel water inside.
- Gaps or splits where old roof layers meet a newer chimney repair.
- Hidden holes or corrosion around metal chimney saddles or crickets.
Water doesn’t always drip exactly where the gap is. On a flat roof, it can travel along the top of the membrane, inside mortar joints, or along framing before finally appearing inside-sometimes ten feet away from the actual entry point. That’s why you’ll see a stain near the chimney on the third floor, but the gap is actually on the uphill side of the chimney on the roof, where wind-driven rain pushes water under a lifted flashing edge. Without tracing the path from stain back to source, you’re guessing. And guesses get expensive.
Quick Self-Check: Is It the Roof, the Chimney, or Both?
You can do a rough diagnosis from the ground and attic:
| Likely Roof/Flashing Issue | Likely Chimney/Masonry Issue |
|---|---|
| You see cracked or lifted roofing material right at the base of the chimney | Bricks are spalling (flaking) or mortar joints are missing |
| There’s a visible gap where the roof meets the brick | You see gaps under metal counter-flashing pieces |
| Someone has smeared tar around the chimney that’s now cracked or pulling away | Stains or dampness appear on the chimney itself inside the home |
Reality check: In many Brooklyn buildings, both the roof flashing and the chimney masonry need attention at the same time for a lasting fix. A roofer who only does membrane work will patch the roof and leave crumbling mortar. A mason who only repoints brick won’t address the failed flashing underneath. You need someone who understands the whole assembly.
Real Fixes for Flat Roof Chimney Leaks (Not Just More Tar)
Stopping a chimney leak for the long haul usually means addressing both the roofing and chimney interfaces, not just slapping on sealant.
| Approach | Best For | What It Involves | How Long It Usually Lasts |
|---|---|---|---|
| Targeted Flashing Repair | Newer roofs with localized flashing failure | Removing failed flashing, installing new base and counter-flashing around the chimney | Several seasons to many years, depending on roof age and conditions |
| Roof & Chimney Joint Rebuild | Older brick chimneys and aging flat roofs | Rebuilding or repointing chimney areas and re-flashing the base | Long-term when done with quality materials and detailing |
| Partial Roof Section Replacement | Flat roofs near end-of-life around the chimney area | Replacing roof layers in a section around the chimney, then installing new flashing | Longer-term, often until rest of roof needs replacement |
On a Park Slope brownstone, the leak was coming through the uphill side of the chimney every time it rained hard. Previous roofer had tarred the downhill side-where there was no leak. We removed the old base flashing, found rotten wood blocking underneath, replaced the blocking, installed new pre-bent aluminum base flashing, cut reglets into the brick joints, and embedded copper counter-flashing. Took a full day. Five years later, still dry.
How We Diagnose and Repair Flat Roof Chimney Leaks in Brooklyn
What to expect from a chimney leak service visit:
1. Interior and Exterior Leak Mapping
We start inside, noting exactly where leaks or stains appear, then inspect the roof and chimney area outside to line up patterns. If you’ve got an attic or crawl space, we look there too-water tracks are often visible on framing before they soak through a ceiling.
2. Close Inspection of Flashing and Chimney Base
On the flat roof, we check all four sides of the chimney, looking at base flashing, counter-flashing, roof seams, and any old tar patches. We’re looking for gaps, corrosion, lifted edges, and whether the flashing is actually embedded in mortar or just stuck to the brick face with caulk.
3. Chimney Condition Check
We evaluate the brick, mortar, caps, and any metal components to see whether water is entering through the masonry itself. Spalling brick, open joints, or a missing crown can let water run down inside the chimney and out through interior walls-even if the roof flashing is perfect.
4. Clear Repair Plan and Photos
We share photos and explain whether it’s mainly a flashing repair, a chimney repair, or a combination, plus what each step involves. No jargon. No upselling a whole roof if you don’t need one.
5. Proper Repair and Re-Flashing
We remove failed materials, repair or repoint the chimney where needed, and install properly integrated flashing tied into your flat roof system. That means cutting reglets, embedding metal, and sealing with compatible products-not gooping tar up the side of the brick.
6. Final Sealing and Follow-Up Check
We seal and detail critical joints, then recommend a follow-up check after one or two heavy Brooklyn storms if needed. If it’s a complex repair, we’ll come back and inspect the interior after the next rain to confirm it’s solved.
Materials and Methods That Actually Work Around Flat Roof Chimneys
Modern Flashing Systems
What we use and why:
- Pre-bent metal base flashing sized for your chimney and roof system.
- Counter-flashing cut into mortar joints, not just surface-glued.
- High-quality sealants compatible with your flat roof membrane.
Supporting Roof and Chimney Work
Often part of a lasting repair:
- Repointing or rebuilding damaged chimney bricks or crowns.
- Repairing blisters, splits, or ponding issues next to the chimney.
- Replacing rotten wood or damaged substrate beneath the roof membrane.
The exact method depends on the roof type-modified bitumen, EPDM, TPO, built-up tar and gravel-chimney construction, and how many times the roof has been re-layered already. On a Williamsburg mixed-use building with a TPO roof, we heat-welded new flashing directly into the membrane and ran it up into reglets cut six inches above the roof line, then covered the top edge with copper counter-flashing. On a Crown Heights brownstone with a coal-tar built-up roof, we embedded the base flashing into hot tar and used lead-coated copper for the counter-flashing to match the existing system. Same goal-watertight intersection-different execution.
What Affects the Cost and Timing of Flat Roof Chimney Leak Repairs?
Chimney leak repairs on flat roofs vary widely in scope-from quick flashing fixes to more involved chimney rebuilds and roof section work.
Key factors we look at:
- Height and size of the chimney and ease of access on your flat roof.
- Roofing material type and number of existing layers.
- Condition of mortar joints, bricks, and any metal caps.
- Extent of roof damage around the chimney (blisters, soft spots, ponding).
- Need for interior repairs once the leak is stopped (handled separately).
Many straightforward chimney flashing repairs can be done in a day. More complex combined roof-and-chimney projects take longer and may be weather-dependent-you can’t repoint brick in freezing temps or torch down modified bitumen in high wind.
What You Can Safely Do Yourself (and What You Shouldn’t)
| Reasonable DIY Steps | Leave These to a Pro |
|---|---|
| Photographing the leak and exterior area for reference | Removing or installing flashing around a chimney |
| Keeping roof drains and gutters clear so water doesn’t back up | Grinding mortar joints for counter-flashing |
| Monitoring leaks after different types of storms and noting patterns | Torching or heat-welding new roofing near combustible chimney materials |
| Working near roof edges or on icy/wet flat roofs |
Warning: Sealant or tar applied over dirty, wet, or moving joints around a chimney is rarely a long-term fix and can hide where water is really entering. I’ve seen homeowners spend $200 on caulk tubes and a weekend on a ladder, only to have the leak come back worse after the first freeze because the sealant cracked and now water’s trapped behind it, rotting the wood deck.
Flat Roof Chimney Leaks We Fix All Over Brooklyn
We work on chimney leaks on flat roofs across Brooklyn-brownstones in Park Slope, walk-ups in Crown Heights, mixed-use buildings in Bedford-Stuyvesant, attached homes in Bay Ridge, and rooftop additions in Williamsburg built around existing chimneys.
Common settings we see:
- Brownstones in Park Slope with older brick chimneys
- Walk-up buildings in Crown Heights with multiple chimneys on one flat roof
- Mixed-use properties in Bedford-Stuyvesant with roof leaks over store ceilings
- Attached homes in Bay Ridge with shared wall chimneys
- Rooftop additions in Williamsburg built around existing chimneys
One Carroll Gardens building had a recurring chimney leak patched five times with tar over eight years. Every patch lasted one winter, then failed. When we finally stripped it down, we found the original 1950s lead flashing was still there-cracked and work-hardened-and every subsequent roofer had just tarred over it. We removed all the old flashing, repointed the bottom six courses of brick, installed new copper base and counter-flashing, and tied it into the existing modified bitumen roof. That was four years ago. Still dry.
Another example: a top-floor tenant in a Bed-Stuy triplex kept getting a drip every time it rained, right next to the chimney. Landlord paid a handyman to caulk around the chimney three times. Leak kept coming back. We inspected and found the membrane around the chimney was fine-but the chimney crown had a two-inch crack, and water was running down inside the flue, then seeping out through a gap in the brick below the roofline. We rebuilt the crown, repointed the exposed brick, and sealed the interior gap. Took half a day. Leak stopped.
Flat Roof Chimney Leak FAQs
Why does my flat roof only leak around the chimney when it’s windy or when it snows?
Wind-driven rain pushes water horizontally under flashing edges and into gaps that straight-down rain never reaches. Snow sits against the chimney base for days, melting slowly and finding every tiny crack. If your leak only shows up in those conditions, you’ve got a gap on the uphill or windward side of the chimney that’s small enough to shed light rain but fails under pressure.
Can you fix just the chimney leak without redoing my whole flat roof?
In many cases, yes. Targeted repair around the chimney is possible if the surrounding roof is in decent shape. But if the roof membrane is brittle, cracked, or near the end of its life, a larger repair may be more cost-effective-because we’ll have to cut into the old roof to install new flashing anyway, and patching around failing material often just moves the problem six feet over.
Will you need to go inside my home or building?
Yes, briefly. Interior inspection helps us map leaks and check for damage behind walls or ceilings. Most work is done outside on the roof and chimney.
How quickly can you respond to a chimney leak in Brooklyn?
Response time depends on weather and schedule, but urgent leak calls are prioritized, especially during stormy seasons. If you’re actively dripping, we’ll get someone out within a day or two to assess and, if possible, do an emergency temporary fix until a full repair can be scheduled.
Stop Your Flat Roof Chimney Leak Before the Next Brooklyn Storm
Every storm pushes more water through weak spots around the chimney. What starts as a drip becomes a stain, then soft drywall, then framing rot-and the repair bill climbs with every season you wait.
When you call for a chimney leak inspection, you get:
- A focused look at both your flat roof and chimney in one visit.
- Straightforward explanations of what’s wrong and how to fix it.
- Repair options tailored to Brooklyn buildings and weather patterns.
Schedule a chimney leak assessment for your flat roof in Brooklyn today, before the next heavy rain makes the damage worse. Call FlatTop Brooklyn or fill out our contact form, and we’ll get back to you within a few hours to set up an inspection. If it’s urgent, say so-we’ll prioritize it.