Flat roof flashing repair is usually a parapet job. The parapet is the short wall that rises above the roof edge on most Chicago two-flats, three-flats and mixed-use buildings. The roof membrane turns up that wall, flashing seals the turn, and a cap or coping sheds water off the top. When any of those three fail, water gets behind the wall or under the membrane, and the first sign is often a stain inside, a few feet from the real opening.
This article covers what fails, how to see it coming, how it gets fixed, and the one permit question that trips owners up.
What is parapet flashing, and what does it do?
A flat roof is a waterproof membrane over insulation over a deck. The National Roofing Contractors Association (NRCA) groups these membranes into built-up roofing, polymer-modified bitumen, rubber sheets (EPDM), thermoplastic sheets (TPO, PVC), sheet metal and sprayed foam (NRCA). Whatever the material, a membrane is sheets, seams and edges, and the wall is where the edge is.
Flashing is the strip of waterproof material that bridges the roof surface and the wall. Brick industry guidance lists parapets, the tops of walls and roofs, chimneys and changes in grade among the places where flashing belongs, and describes it as an impervious layer that collects water that got behind the exterior brick and directs it back out (Brick Industry Association). The same guidance says the main job of caps and copings is to channel water away from the building, and that brick caps, with many mortar joints, may be a poor choice at the most exposed spot compared with concrete, stone or metal (Brick Industry Association).
Put plainly: the top of the wall sheds water, the flashing catches what gets past it, and the membrane has to be tied into both. Three layers, one weak point if any of them lets go.
Why does parapet flashing fail?
There is rarely one cause. The usual ones on Chicago roofs:
- The edge pulls away. The membrane or flashing lifts from the wall, and wind and water get behind it. Seams and edges are where flat roofing is joined, whether by heat, tape, adhesive or torch (Johns Manville), so they are where movement shows up.
- Sealant dries and cracks. Sealant at the top of the flashing is a maintenance item, not a permanent fix. It shrinks and opens over time.
- The coping or cap lets water in. Open joints in a brick or masonry cap let water straight into the wall. The cap is the first line of defense, and the BIA guidance flags mortar joints in caps as the issue (Brick Industry Association).
- Mortar joints in the parapet wall are open. The City's maintenance code lists masonry joints that are not weather resistant or water tight as an unsafe exterior condition (City of Chicago).
- Ponding at the wall. Water that stays on the roof 48 hours or longer can accelerate membrane deterioration and wet the insulation (ARMA). A pond against a parapet loads the flashing constantly. See ponding water on a Chicago flat roof.
On older flat roofs the stain inside is usually on an upper-floor ceiling or wall near an exterior wall, not under the middle of the roof. Painted-over stains that return after every hard rain are a common pattern. The roof gets blamed, the membrane gets patched in the field, and the leak comes back because the water was entering at the wall.
What are the warning signs?
Most of these you can see from a window, the ground or a ladder at the roof edge. Do not walk a wet flat roof.
- Ceiling or wall stains near an exterior wall that grow after rain
- Peeling paint or damp plaster just below the roof line
- Flashing or membrane lifting or bubbling along the wall
- Sealant at the top of the flashing that is cracked, gapped or gone
- Open or crumbling mortar joints in the parapet, or loose bricks on top
- A cap or coping that is cracked, tilted or missing pieces
- Water standing against the wall two days after rain
- Efflorescence (white, chalky deposits) on the parapet face
Loose brick at the top of a wall is a safety issue first and a leak issue second. Bricks have fallen from Chicago buildings onto passersby, including bricks that fell from a two-family home on the West Side in 2016 and injured two people (ABC7 Chicago). If you can see brick moving, keep people away from below and call a professional.
How is a failed parapet flashing fixed?
It depends on how far the damage goes. The honest ladder looks like this:
- Reseal and re-adhere. If the flashing is sound and only the sealant or edge has failed, a roofer can re-secure the edge and reseal the top.
- Replace the flashing. If the material itself has cracked, split or pulled away along a long run, it comes out and new flashing goes in, tied into the membrane.
- Fix the cap or coping. If water is entering at the top of the wall, new flashing underneath will not last. The coping needs repair or replacement.
- Repair the masonry. If mortar joints are open or brick is loose, the wall needs tuckpointing or brick repair before anything is sealed to it. Sealing a failing wall hides the problem for a season.
- Reflash a whole roof section or replace the roof. If the membrane is also at the end of its life, a patch at the wall is money spent twice. Our guide on repair or replace a flat roof walks through how to decide.
Parapet wall work is where roofing and masonry overlap, and it is one of the reasons we do both in-house. For the masonry side, see parapet wall repair in Chicago. For leak tracing on the roof itself, see finding and fixing a flat roof leak.
Does flashing or parapet repair need a permit in Chicago?
It depends, and two City rules point in different directions. Confirm with the Department of Buildings (DOB) before work starts.
- A permit is not required for roof repair limited to 25 percent of the roof area, as long as no part of an exterior wall or roof is cut away (City of Chicago).
- A permit is required for any work on low-slope roofs, even on residential buildings up to four stories (City of Chicago).
- A repair is exempt from a permit only if it does not involve cutting away part of an exterior wall or roof (City of Chicago). Flashing work that opens up the parapet wall can cross that line.
- If the parapet itself is being rebuilt, the City's Express Permit covers a masonry parapet wall up to 2,500 square feet, but not one taller than 48 inches (City of Chicago).
We cannot reconcile the first two for you, and neither can a roofer who is guessing. Ask the DOB about your roof, get the answer for your building, and ask your contractor to name the permit before work starts.
Do two-flats have to file a facade report?
No. The City's exterior wall inspection program applies to high-rise buildings, not to a typical two-flat or three-flat. But every existing building still has to keep its exterior in good repair, and an inspector can cite loose masonry or a damaged parapet after a 311 complaint (City of Chicago).
Water that gets behind a parapet does not stay on the roof. It travels down the wall, into the top-floor ceiling, and into the masonry, where freezing and thawing work on it every winter. A flashing repair that would have been a roof job becomes a roof, masonry and interior job. If the work is done without a required permit, the City can post a stop work order, triple the permit fee in most cases and open an enforcement case, and you may have to correct or remove the work at your own expense (City of Chicago). Rules change, so confirm current details with the Department of Buildings.
Got a stain near a parapet and not sure if it is flashing, the cap or the wall? Our roofing crew can trace it, and see the Chicago roofing guide for how the pieces of a flat roof fit together.
Common questions
Small sealant touch-ups from a ladder are a reasonable DIY job if you can reach the edge safely. Anything involving the membrane, the cap or the masonry belongs with a roofer and a mason, and may need a permit. Check with the Department of Buildings first.
The wall is where the membrane ends and the flashing, cap and masonry take over. If any of the four lets go, water follows the wall down. Open mortar joints, a failed cap, lifted flashing and ponding against the parapet are the usual causes.
Possibly. The City exempts roof repair limited to 25 percent of the roof if no exterior wall or roof is cut away, but also requires a permit for any work on low-slope roofs. Confirm with the Department of Buildings for your roof.
Coping, or the cap, is the top of the parapet wall and sheds water away from the building. Flashing is the waterproof layer that ties the roof membrane to the wall and catches water that gets past the cap. Both have to work.
Sources
- Brick Industry Association: Technical Note 7: Water Penetration Resistance, Design and Detailing (PDF)
- Brick Industry Association: Technical Note 36A: Caps and Copings, Corbels and Racking (PDF)
- City of Chicago: Express Permit Program: Masonry Work
- Asphalt Roofing Manufacturers Association: Ponding Water Basics
- National Roofing Contractors Association: Choosing a low-slope roof membrane
- Johns Manville: SBS Roofing Systems
- City of Chicago: Code Modernization Ordinance, including Title 14X Minimum Requirements for Existing Buildings (PDF)
- City of Chicago: Guide to Building Permits: What Types of Work Do Not Require a Building Permit?
- ABC7 Chicago: Building bricks collapse, injure 2 on West Side (July 25, 2016)
- City of Chicago: Guide to Building Permits: What Happens If I Start Work Without a Required Permit?
Facts last checked: October 7, 2026.
This article explains general rules and common situations in Chicago. It is not legal advice, and City rules change. For a specific property, check with the Chicago Department of Buildings or a licensed professional.