Why Does My Ceiling Only Leak When It Rains?
If your ceiling only leaks when it rains, there is something useful I can tell you before I have even seen it. It is almost certainly not your plumbing.
Your pipes do not know it is raining. The water inside them is under the same pressure on a clear February day as it is in the middle of an August storm. So if a leak appears with the weather and disappears without it, the water is not coming from a pipe. It is coming from outside, and it is getting in through something.
That matters, because it means a plumber is often the wrong person to call. There may be nothing wrong with the plumbing for them to find.
What actually lets the water in
Rain related leaks cluster in the Cape winter, and the same culprits come up again and again:
- Cracks and gaps in walls that absorb water rather than obviously leaking
- Failed or lifted waterproofing, sometimes with water trapped underneath it
- Stormwater pipes buried in walls and slabs, cracked or badly joined, discharging inside the structure instead of outside it
- Cross connected plumbing, where a waste line has been joined into a stormwater line or the other way around
- Balconies where the drainage cannot cope with a downpour
- Sliding doors, windows and seals that draw water in under the rail
- Small openings nobody thinks about, like a weathered outdoor plug point or a disconnected air conditioner drain
Notice that almost none of those are the pipes carrying your drinking water. That is the point.
The obvious suspect is often innocent
A job in Claremont is the one I use to explain this. The client reported water damage in an ensuite bathroom and below the adjacent balcony, and told me plainly that it leaked only when it rained.
The balcony was the obvious suspect, so I tested it first. I blocked off the stormwater drainage, flood tested the balcony, and left it for a full 24 hours. No dye and no water came through the concrete slab below. The balcony was not the problem.
So I flood tested the other stormwater drainage instead, and that is where the answers were. There was a hand basin waste cross connected into a stormwater line draining the roof.
There was a leak in the 50mm stormwater line draining the roof above the stairs. And that leak sat directly above the ensuite shower, which is exactly where the damage was appearing.
Everyone had been looking at the balcony. The water was coming from a stormwater pipe and a badly connected waste.
It is rarely just one thing
A house in Oranjezicht had leaks in three separate places, the kitchen, the study and the main ensuite, and all three appeared only in the rain. Three areas, three different causes.
Above the kitchen, a stormwater drain sat directly over the damaged cupboards. I sealed the pipe and filled it with water, and the level dropped, which proved that line was leaking. In the study, another stormwater drain ran inside the wall with an external downpipe plumbed in right next to it, and up on the top roof I found the drainage pipe in the wall had been sealed off. In the ensuite, I tested the hand basin, the shower, the bath, the wall hung cistern and the grey water drainage, and ran thermal scans across the room. The bathroom plumbing was sound. Nothing wrong with it at all.
One house, one symptom, three unrelated causes, and only one of them anywhere near a bathroom.
Sometimes it is not the building's plumbing or its roof
A job in Camps Bay is my favourite example of how far these can be from where people look. The client reported moisture and damp at the electrical distribution board, noticeably worse in the winter months when it rained.
I pressure tested the fresh water plumbing and found no drop at all. I ran a thermal scan of the bathroom directly above the affected area and found no evidence that the drainage was responsible. On the plumbing side, everything was clean.
So I climbed onto the flat roof above and adjacent to the area, and there it was. A weathered outdoor plug point, corroded inside. And a disconnected drainage pipe from an air conditioning unit, with a large gap underneath it running deep into the wall. A quick dye test showed water could get into that wall easily whenever it rained.
The fix was sealing a gap and replacing a plug point. No plumbing involved anywhere.
Why waterproofing the roof often does not fix it
At a complex in Clifton, a unit reported water coming into the garage. I sealed the stormwater drain to make sure no outside water could enter the system, confirmed there was no flow in the line, then flooded the area above the garage with water containing green fluorescent dye.
The dye came through into the garage. That is definitive: the waterproofing above had failed.
But I also put a 14mm camera through the drainage to check the other possibility, and found no cracks, no joint separation, and no structural faults anywhere in the gully or the connections. So the drainage was fine and the waterproofing was the problem, which is a very different repair to the one people often start with.
The reason this matters: waterproofing is a repair, not a diagnosis. If nobody has proven where the water enters, waterproofing the most likely looking area is a guess. Sometimes the guess is right. When it is not, you pay again.
What the investigation actually involves
It is nothing like a normal leak detection. There is no pressurised pipe to test, so the pressure gauge that finds most leaks is useless here. Instead the job is to recreate the rain, under controlled conditions, and watch where the water goes.
- Flood testing balconies, roofs and landings, sealed off and left for up to 24 hours
- Coloured fluorescent dye, so the water can be seen and identified where it emerges
- Dye absorption tests on cracks and gaps, to see whether they take in water
- Camera inspection inside stormwater pipes cast into walls
- Thermal imaging to find moisture behind a surface
- Testing each drainage line separately, to find cross connections
- The output is a written report with photographs showing what was tested, what was ruled out, and where the water is getting in, so your builder, waterproofer or body corporate can act on evidence instead of a theory.
Frequently Asked Questions
It only leaks in heavy rain, not light rain. Does that mean something?
Do you need to come out while it is raining?
I have had it waterproofed twice and it still leaks. Why?
Could it be rising damp instead?
Do you do the repairs?
How quickly can you come out?
What to do now
If you have a leak that only appears in the rain, the single most useful thing you can tell anyone is exactly that: it happens when it rains, and not otherwise. That one detail rules out most of the plumbing before anyone starts.
If you would like it traced properly, fill in our online form with a photo of the damage and tell me whether it only happens in wet weather.
