Water does not travel vertically
This is the single most useful thing to know about ingress. Once water is inside a structure it follows whatever surface offers least resistance — the underside of a purlin, a screed layer, a conduit, the top of a ceiling board — and it drops at the first place that geometry lets it.
We regularly trace stains back to entry points several metres away, and on more than one occasion on the opposite side of a roof. Sealing the area directly above a stain is the most reliably wasted money in this trade.
On a flat roof the commonest entry point is the edge rather than the field, which is covered under parapet wall leaks. Where the water leaves a white bloom behind as it dries, that is efflorescence and wall salts.
The entry points, in rough order of frequency
- Failed roof detail. Laps, upstands, outlets and penetrations, not the middle of the roof. See roof leak repair in Cape Town.
- Wind-driven rain through a wall. Porous plaster or a hairline crack on the weather elevation.
- Blocked or undersized rainwater goods. A gutter that overflows in heavy rain puts water straight down the wall face.
- Failed wet-area membrane. A shower or balcony leaking into the structure below.
- Below-ground seepage. Hydrostatic pressure through a basement or retaining wall.
- Ground water at slab level. Water running into a garage or ground-floor room across the floor rather than through a wall.
- Plumbing. Worth ruling out early — a slow supply-pipe leak in a wall mimics rising damp closely, and it does not care what the weather is doing.
How to narrow it down before anyone visits
- Does it track the weather? If it worsens during rain it is an envelope problem. If it is constant regardless, suspect plumbing or rising damp.
- Which wind direction? If it only appears in a north-wester, the entry point is on that elevation.
- Does it appear within minutes or over hours? Fast means a direct route — a hole. Slow means it is soaking through something first.
- Is anything wet above it? Check the roof space during rain if you safely can. A wet purlin points uphill to the entry.
- Photograph it wet. The shape and extent when active is far more diagnostic than a dry stain a week later.
A leak is much easier to trace while it is actively leaking. Winter is the worst time to apply waterproofing and the best time to find out what needs it.
Related reading
Start with The Four Types of Damp for the overview, or:
- Moisture in Walls
- Paint Peeling Off Walls
- Musty Smell in the House
- What a Damp Survey Should Actually Cover
Common questions
What does water ingress mean?
Water entering a building where the design did not intend it to. It is an umbrella term covering roof leaks, wall penetration, wet-area membrane failures and below-ground seepage — used before the specific cause is known.
Is water ingress covered by insurance?
It depends on the policy and the cause. Sudden accidental damage is commonly covered; gradual deterioration and lack of maintenance commonly are not, and most ingress falls in the second category. A written finding identifying the cause is what the assessor will want either way.
Why is the damp patch nowhere near the leak?
Because water travels along whatever surface is available inside the structure before it drops. Battens, purlins, screed layers and service pipes all carry it. Tracing has to work uphill from the stain, not straight up from it.