Condensation (commonly encountered)
Condensation occurs when warm, moist indoor air meets a colder surface and the moisture turns to water. It typically shows as black spot mould in corners, around windows, behind furniture and in poorly ventilated rooms. It is often linked to occupation, heating, ventilation and insulation rather than a single building defect, although building defects or poor detailing can also contribute.
Penetrating damp
Penetrating damp is water entering through the building fabric — for example via defective roof coverings, blocked or leaking gutters, failed pointing or render, cracked masonry, or around openings. It is often localised, can appear higher up a wall, and tends to worsen after rain. The fix is to find and correct the point of water entry.
The white salt deposits above are efflorescence — salts left behind as water moves through masonry and evaporates. They are a useful indicator of persistent moisture, but they show where water is emerging, not necessarily where it is getting in.
Rising damp (and why it is over-diagnosed)
Rising damp is ground moisture drawn up through porous masonry by capillary action, usually where a damp-proof course is absent, ineffective or has been bridged (for example by raised external ground or render). It is typically limited to the lower part of a wall and can leave a tide mark and salt deposits.
Bridging of this kind is one of the most common things we look for, and one of the most fixable: where raised ground, a path, a flower bed or added render carries moisture past the damp-proof course, lowering the external level often addresses the cause without any chemical treatment at all.
True rising damp is less common than it is often diagnosed — its symptoms overlap with condensation and penetrating damp, and a free-damp-survey from a firm selling treatment is not impartial. Distinguishing the type correctly, before any chemical injection or replastering, is exactly what an independent inspection is for.
Key takeaways
- Condensation is commonly encountered and is often linked to occupation, heating, ventilation and insulation, although building defects or poor detailing can also contribute.
- Penetrating damp means water is getting in — find and fix the entry point.
- Rising damp is real but frequently over-diagnosed and mistreated.
- The different causes can overlap visually, so correct assessment is important before deciding on remedial works.
- An independent assessment helps avoid paying for the wrong treatment.
Frequently asked questions
How do I know which type of damp I have?
The patterns differ — location, height, timing relative to weather, and salts or mould — but they overlap and are easily confused. An independent inspection can help establish the likely type before money is spent on treatment.
Is a damp-proofing company's free survey reliable?
A free survey from a firm that sells treatment is not impartial. An independent surveyor has no interest in selling you a particular remedy.
Can a survey assess damp evidence in the property I'm buying?
A survey can identify and explain visible damp evidence, comment on likely causes, and recommend further specialist investigation where required before you commit.
This guide is general information, not advice on a specific property. Every building differs — for findings specific to a property you are buying, book a survey.