Flat roofs don't leak where you think they do. Water gets in at a seam or flashing, runs along the deck or between old layers, and drips out wherever the ceiling gives it a path, sometimes several feet away. That is why so many flat roof "repairs" are a blob of tar over the spot above the stain, and why the leak is back after the next storm. Here is where flat roofs actually leak and how a proper repair is done.
Where flat roofs actually leak
- Wall and parapet flashing. Where the roof turns up a brick wall, the flashing can pull loose, or water can get in above it through open mortar joints. This is the most common leak on Pittsburgh houses.
- Party walls. On row houses, the seam where your roof meets the neighbor's is a frequent entry point.
- Seams. EPDM seams that were not cleaned and primed well open up over time; TPO welds can fail if they were made at the wrong heat.
- Penetrations. Plumbing vents, exhaust fans, skylights, hatches and chimneys each have a flashing that can crack or come loose.
- Drains, gutters and scuppers. When the rear gutter or a drain clogs, water backs up over flashings that were never meant to be underwater.
- Punctures and blisters. Dropped tools, branches, foot traffic, and blisters that crack open.
How a leak is traced
Start inside: where is the stain, and does it show up in every rain or only in wind-driven rain or snowmelt? Then on the roof, start above the stain and work outward and uphill, since water runs toward the low side. Every flashing, seam and penetration in that area gets checked by hand. Soft decking or wet insulation underfoot shows where water has been traveling. When a detail is suspicious but not obviously open, running water over it while someone watches inside confirms it. The result should be a photo of the actual failure, not a guess.
Roof leaking right now?
Pittsburgh Superior Flat Roofing repairs and replaces flat roofs on Pittsburgh homes, row houses and businesses, with a written price before any work starts. Request a quote online and we’ll call you back.
What a proper repair looks like
EPDM (rubber)
The area is cleaned of dirt and old sealant, primed, and covered with an EPDM patch or seam tape that extends well past the damage, with the edges sealed. Flashings are rebuilt with uncured EPDM flashing around corners and penetrations. See EPDM vs. TPO vs. modified bitumen.
TPO
The surface is cleaned and a TPO patch is heat-welded on. Older, weathered TPO may need special cleaning before it will take a weld.
Modified bitumen and built-up
Damaged plies are cut out and replaced with new modified bitumen, lapped and sealed into the surrounding roof. Blisters are cut, dried and patched.
Flashing on brick
If water is getting in above the flashing, the fix is in the wall: repointing, a new counter-flashing set into a cut joint, or new coping on the parapet. More membrane on the roof won't stop water that is coming through the bricks.
Why tar isn't a repair
Roof cement is fine for an emergency, but it dries out, cracks and pulls away within a season or two. It doesn't bond well to rubber, and every layer of it has to be scraped off before a real patch can go down. If your roof has black blobs in the same places year after year, those are the spots that were never actually fixed.
When repair stops making sense
If the roof has been patched in many places, the decking is soft, there are two or three layers underneath, or the membrane is cracked all over, you are paying for repairs on a roof that is finished. See repair vs. replacement costs.
The bottom line
A flat roof leak repair is only as good as the leak tracing behind it. Find the entry point, photograph it, fix it with the roof's own material, and check the drains while you are up there. See flat roof repair, or if water is coming in now, what to do right away.