Damp
Rising damp investigation and treatment
Careful assessment of low-level dampness, which is frequently caused by something other than rising damp.
Read this first
Low-level moisture does not automatically mean rising damp
Rising damp is the upward movement of ground moisture through porous masonry by capillary action, where there is no effective barrier to stop it. It is a real defect and we treat it — but it is diagnosed far more often than it occurs, because several much more common problems look exactly like it.
Before we attribute damp to capillary rise, each of these has to be considered and, where relevant, ruled out:
Rainwater splashing back from hard paving or a raised patio
External ground levels above the internal floor and the damp-proof course
Render, pointing or a screed bridging the damp-proof course
Debris or spoil bridging a subfloor void
A leaking heating or water pipe within or below the floor
Condensation on a cold, poorly ventilated ground-floor wall
Hygroscopic salts in old plaster holding atmospheric moisture
Water penetration at low level through defective masonry
An electrical moisture meter reading, taken alone, does not establish rising damp. Those instruments respond to conductivity, and salt-contaminated plaster is highly conductive whether or not the wall behind it is wet.
What the issue is
Rising damp is moisture drawn upwards through porous masonry from the ground by capillary action. It is far less common than low-level dampness generally, and a confident diagnosis needs supporting evidence rather than a meter reading alone.
Common symptoms
- Dampness concentrated within the lowest 1m of a wall
- A tide mark or salt band
- Blown plaster at skirting level
- Decayed skirting boards
- Damp that persists in dry weather
Likely contributing factors
- Absent, bridged or breached damp-proof course
- Raised external ground or paving
- Solid floor to wall junction detailing
- Internal render bridging the DPC
- Debris in a subfloor void
Conditions that may be mistaken for it
- Penetrating damp at low level
- Condensation on cold ground-floor walls
- Hygroscopic salts holding moisture
- A leaking heating pipe within the floor
How the issue should be investigated
- Establish wall construction and floor type
- Check external ground levels against internal floor level
- Locate any existing damp-proof course
- Profile moisture at varying heights
- Consider salt contamination and plaster condition
Potential treatment or repair options
- Correcting external ground levels or bridging
- Repairing defective pointing or render
- Chemical damp-proof course where confirmed as appropriate
- Replastering with a suitable damp-resistant specification
- Allowing controlled drying
When treatment may not be appropriate
- Where the pattern and evidence do not support capillary rise
- Where a bridging defect can simply be removed
- Where existing plaster is sound and only decoration is affected
Factors affecting the cost
- Linear metres of wall involved
- Whether plaster removal and replastering is needed
- Skirting and radiator removal
- Waste disposal
- Occupied working conditions
What to expect during an inspection
The surveyor will examine the affected walls internally and externally, assess the floor and wall junction, take a moisture profile and record ground levels.
How we investigate
How rising damp is properly investigated
The purpose of the investigation is to establish whether moisture is genuinely moving up through the wall, and if so, why the wall is no longer protected.
- 1
Establish the construction
Solid or cavity wall, wall thickness, floor type, the position of the internal floor relative to external ground, and whether a damp-proof course exists and where it sits.
- 2
Profile the moisture
Readings taken at low, mid and high level across the affected length, so the distribution can be seen. Capillary rise produces a characteristic reduction with height; a leak or penetrating defect usually does not.
- 3
Look outside
Ground and paving levels, air bricks, render terminations, pointing, rainwater discharge and anything abutting the wall that could carry water across the damp-proof course.
- 4
Measure the room
Air temperature, relative humidity, dew point and surface temperature, so condensation can be identified or excluded rather than assumed.
- 5
Sample where it matters
Where the diagnosis carries significant cost, drilled samples can be tested to establish moisture content and the presence of hygroscopic salts, which separates a wet wall from a salt-affected finish.
This is the stage that most often changes the answer — and the price.
Treatment follows diagnosis
What we recommend when rising damp is confirmed
Where the evidence supports capillary rise, the remedy has two halves: restore an effective barrier, and deal with the salt-contaminated plaster that will otherwise keep the wall looking damp.
Where it is not supported, we say so, and the recommendation is the repair that actually addresses the moisture — which is frequently outside the building.
- Correcting external ground levels, paving and bridging first
- A remedial damp-proof course where the wall's protection has failed
- Membrane lining where a chemical course is unsuitable
- Removal of salt-contaminated plaster to the extent required
- Replastering to a damp-resistant specification, or a dry lining system
- A stated drying period before redecoration
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.
Damp proofing
Why damp proofing is not one treatment, and how the right remedial specification follows the diagnosis.
Damp-resistant plastering
Reinstatement in the right materials once the cause has been dealt with and the wall has begun to dry.
Penetrating damp investigations
Rainwater and external defects traced to the elevation, opening or rainwater fitting responsible.
External damp-related repairs
Pointing, render, rainwater goods and ground levels put right so water stops reaching the wall.
Condensation control
Humidity, dew point and surface temperatures measured before any equipment or insulation is recommended.
Where we work
Rising damp investigation across Bedfordshire, Northamptonshire and Cambridgeshire
Rising 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.