Flat Roof Leaking Where It Meets the Wall? Parapet Leaks
When a flat roof leaks where it meets a wall, the water is usually getting in at the joint: the flashing where the roofing turns up the wall, the cap on top of a parapet wall, or a scupper through it. Water runs down the wall or stands against it, and any gap at that joint lets it in.
Call or text photos to (725) 502-3114 for a free, no-pressure inspection and a written estimate before any work begins.
Why the wall joint is the weak spot
A parapet is the short wall that rises above the edge of a flat roof. Where a flat roof meets a parapet or the wall of the house, the roofing has to turn up the wall and be sealed at the top of the turn. A strip of metal or a sealed edge above it keeps water from running down behind it.
The top of the parapet has its own cover, the parapet cap. Every piece of that joint is a lap or a seal, not one continuous sheet like the open roof.
In Las Vegas, flat and low-slope sections are common on modern homes, additions, patio structures and older central-valley houses. Homes that mix steep tile with flat and low-slope sections, parapets, and complex transitions have all the classic leak locations in the desert.
Where the joint fails in Las Vegas
Sun and heat. The flashing and sealant at the top of the turn-up face the sun all day. Sealants dry and crack, and the edge pulls loose.
Daily movement. The roof and the wall heat up and cool down at different rates. That movement works at the joint until a seam opens.
The parapet cap. Seams in the cap open, fasteners loosen, or the seal under it fails. Water gets into the top of the wall, runs down inside it, and shows up below the roof line.
Cracks in the wall. A crack in the stucco or block of a parapet lets water into the wall behind the flashing, so the roof can look fine while the ceiling still stains.
Wind-driven rain. Monsoon wind drives rain against the wall and down into the joint at its base.
Roofs with no parapet can leak at the edge for the same reason. The edge metal is a lap over the roofing, and its seal dries out.
Where an addition joins the house
A flat roof on an addition, a patio structure or an enclosed room often meets the house at a wall, or under the edge of the main roof. That tie-in is a roof-to-wall transition. If its flashing was never done right, or water from the main roof pours onto it, the leak shows up right along the wall the two share.
Look for a stain on the ceiling that runs along that wall, or a stain on the wall itself just below the ceiling.
Scuppers and drains near the wall
A scupper is an opening through the edge wall of a flat roof that lets water run off. Where it passes through the parapet, the roofing has to be sealed around the opening on every side. When that seal fails, water that should leave the roof goes into the wall instead.
A drain has a seal where the roofing meets the drain. A leak right around a drain is often that seal rather than the pipe below it.
Standing water and clogged drains are a separate problem, covered in our article on flat roof leaks: ponding, seams, scuppers and drains.
What you can check from the ground
Please do not walk on the roof. Look from the ground, from a window or from the yard.
Inside, notice whether the stain runs along a wall, sits in a corner, or shows up on the wall below the roof line. Outside, look at the parapet for cracks, stains or white streaks running down from the top, and for a cap with gaps or loose pieces.
After rain, look at the scuppers. Water coming out of the wall below a scupper, instead of out of the scupper, points to the seal around it. Take photos inside and out. Send the photos to (725) 502-3114 and we can tell you what we see.
What we do
We trace the leak from the stain back to the roof. Along a wall, that means the flashing, the cap, the scuppers and drains, and anything that goes through the roof near the wall. If the roof does not give the answer away, controlled water testing confirms the entry point before we repair. See how we find a roof leak.
We detail parapet caps, complex flashing, and penetrations, and install reflective TPO/PVC membrane on flat and low-slope sections, the spots where these roofs most often leak. Flashing at walls and roof-to-wall transitions is part of our roof repair work.
We show you what we found and why it leaks. Every leak repair we perform is backed by a 5-year warranty. If a leak we repaired returns within that period, we come back and make it right.
A repair or a new membrane?
A failed flashing edge, a cap seam or a scupper seal is often a repair. A failed flashing edge is resealed or rebuilt, and a failed seal is redone where it gave out.
It is a bigger job when the roofing along the wall has worn through, or the whole roof has reached the end of its life. Then the lasting fix is a properly installed reflective TPO or PVC membrane with correct slope-to-drain detailing, sealed penetrations, and watertight flashing at every wall and curb. The seams in these membranes are heat-welded into a continuous surface. Where the roof will not drain because of its slope, we can look at correcting the slope where that is feasible.
We do not install spray foam or torch-down roofing. If your roof currently has foam or torch-down, we can assess it and talk through a membrane re-roof. See our TPO and PVC roofing page.
Frequently Asked Questions
Why does my flat roof leak along the wall and not in the middle?
The open roof is one continuous surface. The joint at the wall is a lap and a seal, and sun, heat and movement work at it every day.
What is a parapet cap?
The cover on top of a parapet wall. If its seams or the seal under it fail, water gets into the top of the wall and can show up inside below the roof line.
My flat roof leaks where the addition joins the house. Why?
That tie-in is a roof-to-wall transition. If its flashing was never done right, or water from the main roof pours onto it, it leaks along the shared wall.
Can it be fixed without a new roof?
Often, yes. A failed flashing edge, cap seam or scupper seal can be repaired. A new membrane is for roofs at the end of their life.
Who do I call?
Call or text photos to (725) 502-3114.