Damp
Penetrating damp investigation and repair
Investigation of moisture entering through walls, roofs, openings and rainwater goods.
Where the water comes in
Penetrating damp is a building-fabric defect, not a wall disease
Penetrating damp is moisture passing through the external fabric of the building into the interior. The cure is nearly always a repair to the fabric, which is why the investigation concentrates on finding the defect rather than treating the wall.
The defects we find behind the great majority of cases:
Cracked, hollow or blown render, and render terminated below ground level
Eroded, cracked or inappropriate pointing
Spalled, frost-damaged or porous brickwork
Blocked, leaking, misaligned or undersized gutters
Split, loose or discharging downpipes and gullies
Slipped, cracked or missing roof coverings
Defective chimney flaunching, pots and lead flashings
Failed or missing cavity trays and lintel details
Perished mastic and sealant to windows and doors
Defective or missing window cills and drips
Cracked masonry, movement joints and open perpends
Ground levels, paving and drainage directing water at the wall
Cavity walls are not immune. Mortar snots on wall ties, debris in the cavity, partial-fill insulation displaced during installation and bridged cavity trays all carry water across a cavity that was designed to stop it.
What the issue is
Penetrating damp occurs where water passes through the building envelope from outside. It is often intermittent and closely linked to rainfall, wind direction and the condition of external details.
Common symptoms
- Damp patches that appear or worsen after rain
- Staining below windows or at wall heads
- Damp around chimney breasts
- Localised mould in one area only
- Water marks on ceilings
Likely contributing factors
- Blocked or leaking gutters and downpipes
- Cracked render or failed pointing
- Defective window seals and sills
- Roof and flashing defects
- Cavity debris or wall tie bridging
Conditions that may be mistaken for it
- Condensation in cold corners
- Rising damp at low level
- Internal plumbing leaks
- Escape of water from appliances
How the issue should be investigated
- External elevation inspection, including rainwater goods
- Correlating damp locations with external features
- Assessment of render, pointing and openings
- Roof and chimney inspection where accessible
- Moisture mapping internally
Potential treatment or repair options
- Repair or replacement of rainwater goods
- Repointing or render repairs
- Sealing and flashing repairs
- Cavity clearance where appropriate
- Redecoration once dry
When treatment may not be appropriate
- Where the source has already been repaired and the wall is drying
- Where internal tanking would mask an untreated external defect
Factors affecting the cost
- Height and access, including scaffolding or towers
- Extent of external repair
- Materials to match existing finishes
- Number of elevations affected
What to expect during an inspection
Expect an external inspection in addition to internal readings. Weather conditions on the day can influence what is visible.
The most useful clue you can give us
Damp that gets worse after heavy rain
If a patch darkens or spreads within a day or two of heavy or wind-driven rain, and recedes during dry spells, that correlation is diagnostic evidence worth more than any single reading. It points strongly towards water entering the fabric, and it tells us to look at the elevation exposed to the prevailing weather.
It is not proof by itself. Wet weather also brings higher humidity, colder surfaces and closed windows, all of which increase condensation, so we still measure the internal environment before concluding. But a rain-correlated pattern changes where we spend our time — on the outside of the building, in the right weather.
What we inspect when the pattern follows the rain:
- The full elevation above and around the internal damp, at height where accessible
- Render and pointing condition, and any cracking following a mortar bed or perpend
- Rainwater goods under load, including joints, gullies and discharge points
- Roof edges, verges, valleys, abutments and parapet details
- Chimney stacks, flaunching, pots and flashings
- Window and door surrounds, cills, drips and sealant
- Ground levels, splashback zones and surface water run-off
How we work
From internal symptom to external defect
- 1
Map the damp internally
Position, height, shape and extent recorded, with moisture profiled across the area. The shape of a patch often identifies the route: a wide low band behaves differently from a plume below a window or a stain following a joist.
- 2
Inspect the elevation
The outside face above and around the affected area is examined in detail, along with rainwater goods, roof interfaces and openings. Binoculars, pole cameras or access equipment are used where height demands it.
- 3
Rule out the alternatives
Internal conditions are measured so condensation can be excluded, and plumbing is considered where the pattern or location suggests it.
- 4
Confirm the route
Where the defect is not conclusive on inspection, thermal imaging, controlled water testing or monitoring during wet weather is used to confirm it before work is specified.
- 5
Repair, dry, then reinstate
The fabric defect is corrected, the wall is allowed to dry, and internal reinstatement — if it is needed at all — follows rather than precedes the repair.
Sealing or painting the inside face of a wall that is taking water from outside moves the problem, it does not solve it.
Related work
Related work and reading
Damp surveys and moisture investigations
What a professional damp investigation covers, what the instruments can and cannot establish, and what your written report contains.
External damp-related repairs
Pointing, render, rainwater goods and ground levels put right so water stops reaching the wall.
Damp proofing
Why damp proofing is not one treatment, and how the right remedial specification follows the diagnosis.
Rising damp assessments
Capillary moisture, damp-proof courses, bridging and salt contamination assessed on the evidence rather than a meter reading.
Damp-resistant plastering
Reinstatement in the right materials once the cause has been dealt with and the wall has begun to dry.
Mould remediation
Safe removal of the contamination, and control of the moisture conditions that allowed it to grow.
Where we work
Penetrating damp investigation across Bedfordshire, Northamptonshire and Cambridgeshire
Penetrating damp investigation is carried out across our operating area. Choose your county or town to see the work we do locally, the postcode districts we cover and how to arrange an inspection.
Frequently asked questions
Next step
Not sure which inspection you need? Start with a few questions.
Tell us what you are seeing and we will set out what is likely, what is uncertain and which inspection would answer the question. Speak to us on 0333 335 6152 if you would rather talk it through.