Where is my flat roof leaking?
Stain on your top-floor ceiling or water running down the wall? Tap a number to see where the water could be getting in on a flat roof and where it shows up inside.
StormBear installs torch-down flat roofs. Torch-down roofing is a flat-roof system made of layered asphalt sheets that are heated with a torch to seal them together and to the roof. It is also called modified bitumen.
Have a sloped shingle roof? See where shingle roofs leak →
Where water is supposed to go
A flat roof isn't perfectly flat. It slopes a little, about a quarter inch per foot, so water runs off.
Where flat roofs leak, and where it shows up inside
This two-flat is cut open. Tap a number to follow the water from the roof to the top-floor apartment.
1. Parapet caps
GETS IN
Loose metal caps or dried-out joints on top of the parapet wall.
TRAVELS
Straight down into the brick, inside the wall and behind the roof flashing.
SHOWS UP INSIDE
A stain or wet plaster high on a top-floor wall, near the ceiling.
Why water gets behind the roof
Look at numbers 1 and 2 on the drawing. On a brick two-flat, water often gets in above the roof, through the parapet caps or cracked mortar, and runs down inside the wall, behind the roof flashing. That's why a brand-new roof alone doesn't always stop a leak. The parapet walls and caps have to be fixed too.
Common mistakes roofers make
- Torching new roofing over old layers or wet roofing, which traps water and hides rotten wood.
- Seams that weren't heated enough. A good seam shows a thin line of melted asphalt along the edge.
- Running the roofing only a few inches up the parapet wall, instead of up and under a metal counterflashing.
- Reusing loose or rusted parapet caps, or sealing them with caulk only.
- Not building in slope, so water sits in the same low spot after every rain.
- Scuppers that are too small or set too high, so water has to pond before it drains.
- Patching with tar again and again instead of fixing what's causing the leak.
How to check your flat roof safely
After a rain
Look from a back window or porch. Water should be gone within 2 days.
Parapet caps
From the street or yard, the metal caps should sit flat with no gaps or rust.
Downspout
Watch it during a rain. A dry downspout in a storm means something is clogged.
Top-floor ceilings
Look for stains along the outside walls and toward the back of the building.
Black sand
Grit piling up at the bottom of the downspout means the surface is wearing out.
Stay safe
Never walk on a roof that feels soft, and never go up in rain or ice.
Seeing a stain on your top floor? We check the roof, the parapet walls and the caps on every flat roof inspection.