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Penetrating damp: finding where the water actually gets in
Penetrating damp is water crossing the building envelope from outside, and the single most useful thing to know about it is that the damp patch is rarely below the defect. Water entering at a roof junction travels along joists, down cavities and across lintels before it finds a surface it can wet. Diagnosis works backwards from the stain.
How it behaves
- Damp that appears or worsens after rain and eases in dry spells
- A patch with a defined edge and often a darker centre, rather than an even band at low level
- Damp appearing on upper floors or on ceilings, which rising damp cannot reach
- Worse on the elevation that takes the prevailing weather, and absent on the sheltered side
- Staining around chimney breasts, window reveals, and where an extension meets the original wall
Where it usually comes from
Rainwater goods first. A blocked or overflowing gutter puts a continuous sheet of water down one strip of wall throughout the wettest months, and it finds every defect in the pointing. Hoppers that overflow only above a certain rainfall produce damp that looks mysterious because it is intermittent. Both are cheap to fix and are among the most common causes we find.
Roof junctions and flashings next: chimney flashings that have lifted, a valley or parapet gutter that has failed, and above all the junction where a rear or side extension roof meets original brickwork. That last one accounts for a large share of first floor damp patches across the South East, because a shallow chase or a low upstand looks perfectly acceptable and leaks in driving rain.
Then the wall itself. Failed or eroded pointing, cracked or blown render, tile hanging with slipped or frost damaged tiles, and cavity wall insulation that has slumped or bridged. Each has a signature: bridging cavity fill shows on the weather side after driving rain, failed render shows where the render has failed, and tile hanging shows nothing at all from the ground.
How we trace it
Internal readings establish where the water is arriving and how much of it there is, and the pattern tells us which elevation and roughly what height to concentrate on outside. Then the work is external and it is methodical: rainwater goods, roof coverings and junctions, flashings, pointing, render, glazing details, ground levels and drainage, in that order.
Where the elevation cannot be seen properly from the ground, it has to be seen properly another way. Tile hanging, high level flashings and parapet detail cannot be assessed from a garden, and a survey that reports on them from there is guessing.
Putting it right
The repairs are usually building repairs rather than damp treatments: clearing and realigning gutters, renewing a flashing, repointing in a mortar suited to the wall, cutting out and replacing failed render in a permeable system, or replacing slipped tiles and the felt behind them. On solid walls the material matters, because a cement repair on a lime built wall solves this year and causes the next problem.
Where DampScan carries out the repair it is covered by an insured workmanship guarantee. Where the right answer is a roofer or a drainage contractor, the report says that instead, and you are under no obligation to use us for anything.
Find the defect, not just the damp patch
Internal readings, a full external inspection including the parts that cannot be seen from the ground, and a written report within 24 hours of the visit.
Book a surveyOr call 07386 225526.
Questions
Why is the damp patch nowhere near the leak?
Because water follows the easiest path available and only becomes visible where it reaches a surface it can wet. Entering at a roof junction it may run along a joist, down a cavity or across a lintel and appear a floor below and several feet sideways. That is why examining only the stained wall establishes that the wall is wet and nothing more, and why the external inspection is the part that actually answers the question.
It only leaks in certain weather. Is that useful?
Extremely. Damp that appears only in driving rain from one direction points at a specific exposed elevation and usually at render, pointing or cavity fill. Damp that appears only in prolonged heavy rain points at gutters and hoppers that cope until they do not. Damp that is constant regardless of weather points at plumbing or drainage instead. Tell us what you have noticed and when; it narrows the search considerably.
Could cavity wall insulation be the cause?
It can be, and it should be checked rather than assumed. Retrofit fill can settle over time and leave the top of the wall uninsulated, or bridge the cavity so water crosses from the outer leaf to the inner one. The signature is damp on the most weather exposed elevation, appearing after driving rain and drying between events, rather than constant damp at low level. We inspect for it directly and report what was found.