Why most roof leaks are misdiagnosed

It started as a shadow on the passage ceiling. You painted over it and it came back through by August. Then somebody came out, went up on the roof for twenty minutes, put something black on something, and charged you two and a half thousand rand. It was fine all summer. First real front of the winter and there it is again, slightly bigger, slightly further along the passage.

Now you are being told the roof needs to be redone. Maybe it does. But there is a very good chance that nobody has yet worked out where the water is actually getting in, and until somebody does, every rand you spend is a coin flip.

This is the most common failure in our trade, and it is not usually dishonesty. It is that proper diagnosis is slow, unglamorous, and impossible to do in the twenty minutes a free quote is worth to the person doing it.

Water is a patient traveller. It gets in at one point, then follows whatever it finds: the underside of a sheet, a batten, a rafter, a screw thread, a pipe, a fold in the sisalation. It runs sideways for metres. It runs along a purlin to the low end of the roof. Only when it finally meets something absorbent, usually a ceiling board, does it show itself.

So the stain marks the lowest point on the water's journey, not the entry. On a pitched roof the entry point is almost always uphill of the stain, often several metres uphill, and frequently on the other side of a wall. We have traced a bedroom stain in Welgemoed back to a cracked parapet capping on the far side of the house.

The stain tells you where the water gave up. It tells you nothing about where it started.

Which is why sealing the ceiling, painting over the mark, or coating the wall directly below it changes nothing at all. Those treat the symptom at the exact point where the water has already finished its work.

1. 1Penetrations. Vent pipes, flues, aerial mounts, geyser overflows, satellite brackets and above all solar mountings. Anything that was drilled through the roof after the roof was built. This is the number one source on modern houses, and solar has made it dramatically worse.
2. 2Flashings and abutments. Where the roof meets a higher wall, a chimney or a parapet. The original detail is often just mortar and mastic, and mortar cracks.
3. 3Parapet capping. Water sits on top of a flat parapet, finds a crack in the mortar bed, and then runs down inside the cavity for metres before appearing inside. A coating on the wall face does absolutely nothing about this, and it is the single most misdiagnosed leak we see.
4. 4Fixings. Every screw through a metal or fibre cement roof is a hole with a washer that has a lifespan. On a twenty year old roof, the washers are done.
5. 5Blocked or under-sized drainage. Gutters full of oak leaves, a box gutter with a flat fall, an overflowing valley. The roof is fine. The water simply has nowhere to go and backs up over the flashing.
6. 6Slipped, cracked or lifted tiles on the weather side. In Cape Town, the weather side is the north west, and one displaced tile can feed a leak three rooms away.
7. 7Failed old membrane on a flat roof. Torch-on that has blistered, shrunk back at the edges or split at the laps. Usually visible only if somebody actually goes and looks at it.

You do not need to know anything about waterproofing to test whether somebody has done the work. Ask them to walk you through it.

• Can they state the entry point, in a sentence, and point at a photograph of it?
• Did they go into the roof space? Almost every diagnosis is confirmed from inside, in the dark, looking for daylight and tide marks on the timber. If nobody has been in the roof, nobody has diagnosed anything.
• Did they look at the drainage as well as the roof? A shocking number of leaks are a gutter problem.
• Does the water path they describe account for the position of your stain, including which side of the house it is on?
• Have they distinguished this from condensation and from a plumbing leak? A geyser overflow, a shower waste and a burst hot water pipe all produce ceiling stains, and none of them are roof leaks.
• Is the quoted scope the size of the diagnosed problem, or is it the size of the roof?

We get on the roof, and we go into the roof space. Both, every time. We photograph the substrate, the flashings, the parapets, the penetrations and the drainage, and we photograph the underside of the deck where the water has been running, because timber keeps a record.

Then we map the path backwards from your stain. If we can get there on a wet day and watch it happen, better still, and we will ask you for that if the diagnosis is not conclusive dry. Where it is genuinely ambiguous we will hose test in stages, working uphill, one detail at a time, with somebody inside watching.

The rule we hold ourselves to is simple. If we cannot explain the water path to you in one clear sentence, we have not diagnosed it yet, and we will not quote a system until we can. That written diagnosis becomes the scope of the quote, which is why our quotes read differently to a one line price.

The point of the diagnosis is that sometimes the answer is small. If your leak is one parapet capping and two flashings, we would rather do that properly than sell you four hundred square metres of membrane you do not need. The second phone call, when it does not leak next winter, is worth more to us than the bigger invoice.

• Where exactly is the water getting in? Show me the photograph.
• Did you go into the roof space?
• What is the scope, detail by detail, and what is deliberately excluded?
• How many coats, which product by name, and what does the guarantee cover?
• If it leaks again in the same place next winter, what happens?
• Is there a cheaper, smaller fix that would actually solve this, and why is it not what you are recommending?

The last one is the honest test. Anybody who cannot answer it has not thought about your roof, only about their invoice.