Rising damp is one of the most contentious topics in building pathology. While true rising damp does exist, it is far less common than the damp-proofing industry would have property owners believe. Accurate diagnosis is essential to avoid unnecessary and expensive remedial work.
True rising damp is the upward movement of ground moisture through masonry walls by capillary action. It occurs where there is no effective damp-proof course or where an existing DPC has been bridged by raised external ground levels, internal floor levels or rendering. In genuine cases, a tide mark is typically visible up to around one metre high, with hygroscopic salt deposits on the plaster surface.
The majority of damp problems at low level in London properties are caused by condensation, penetrating damp from defective rainwater goods, high external ground levels, blocked sub-floor ventilation or plumbing leaks. Electrical moisture meters, widely used by damp-proofing companies, give elevated readings in the presence of salts and cannot distinguish between moisture from different sources. This leads to widespread misdiagnosis of rising damp.
Proper diagnosis requires a methodical investigation. This includes visual inspection, assessment of external ground levels and drainage, examination of sub-floor ventilation, measurement of internal humidity, and where necessary, gravimetric moisture testing of wall samples taken at different heights. An independent chartered building surveyor will take this systematic approach rather than relying on electrical meters alone.
Where true rising damp is confirmed, the first step should always be to address external causes: lowering external ground levels, reinstating sub-floor ventilation, repairing rainwater goods and clearing blocked drains. Chemical injection may be appropriate in some cases, but only after external factors have been resolved. Replastering with salt-resistant plaster may also be needed where salts have contaminated the existing plaster.
Yes, but it is far less common than often claimed. Many cases are misdiagnosed condensation, penetrating damp or the result of high ground levels, defective drainage or blocked sub-floor ventilation.
Rising damp produces a tide mark up to around one metre with salt deposits. Condensation appears on cold surfaces and is worse in poorly ventilated rooms. Gravimetric testing, not just electrical meters, can distinguish between them.
In most cases, no. Address external causes first: ground levels, ventilation, drainage and rainwater goods. Chemical injection may be appropriate only after proper diagnosis and external factors are resolved.
Commission an independent assessment from a chartered building surveyor with no commercial interest in selling remedial work before committing to expensive treatment.
Independent damp diagnosis using proper investigation techniques and gravimetric testing.
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