Key points
- The main types: condensation (from water vapour inside the home), rising damp from the ground, and water penetration through walls and roofs, plus plumbing leaks.
- Successful treatment depends on correctly diagnosing the type of dampness.
- Electrical moisture meters can lead to misdiagnosis when used alone; monitoring indoor temperature and humidity with regular logging is the most effective method, according to BRE.
- Rising damp is usually linked to a missing or ineffective damp-proof course or membrane (DPC/DPM).
Written for:OwnerContractor
A damp patch on a wall can have more than one cause. And the UK Building Research Establishment (BRE) says: successful treatment can only be achieved if the type of dampness is correctly diagnosed1.
1) Types of dampness
| Type | Source | Common signs (practical) |
|---|---|---|
| Condensation | Water vapour produced by normal building use moves freely around the building and may condense on surfaces or within the building fabric1. | Mould in corners and behind furniture, droplets on glass, on cold pipes and around AC outlets. |
| Rising damp | Ground moisture, usually associated with missing or ineffective damp-proof courses or membranes1. | Low on walls, a roughly horizontal tide line, white salt deposits. |
| Water penetration | Water entering through walls or roofs from component failure or construction not robust enough1. | Worse with rain or roof washing, near windows, upstands and cracks. |
| Plumbing leaks | Water and drain pipes inside walls and floors. | Constant regardless of weather, near bathrooms and kitchens. See leak detection. |
2) Diagnostic methods and their limits
BRE reviews four approaches1:
- Visual inspection: essential, but potentially the least reliable on its own.
- Moisture meters: helpful, but can lead to misdiagnosis depending on the wall material and building complexity.
- Laboratory techniques: such as carbide moisture testing and analysis of soluble salts in drilled samples.
- Monitoring indoor temperature and humidity with regular logging, described as the most effective way to diagnose damp.
Beware quick diagnoses: if someone says "this is rising damp" after only touching the wall with a meter, ask them to explain the other evidence before any injection or breaking-out.
3) Treatment by cause
General practical guidance that follows the diagnosis.
- Condensation: ventilation and extract fans in bathrooms and kitchens, fewer vapour sources, and dealing with cold surfaces (thermal bridges, uninsulated AC pipes).
- Rising damp: fix the damp-proof layer and drainage around the building; in new builds, waterproof foundations and ground beams before backfilling.
- Penetration from outside: repair cracks and joints around windows, and roof and upstand waterproofing. See waterproofing and joint sealants.
- Plumbing leaks: fix the leak first, then wait for the wall to dry before painting.
4) After treatment: painting
Fix the moisture source first, and if efflorescence keeps appearing, delay painting2. See paint problems.
Sources
The number next to a statement points to its source in this list. Sources back the general information; anything marked “practical advice” is editorial experience, not a quoted source. Anything that affects safety, structural design or electrical installations needs a licensed professional, and in Saudi Arabia the binding reference is the Saudi Building Code.
- 1Diagnosing the causes of dampness in buildings — BRE (Building Research Establishment)
- 2How to Fix Efflorescence (white crystal deposits) — Sherwin-Williams
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This guide is for general information and planning, based on standards and technical guides. Standards are revised periodically; in Saudi Arabia the binding reference is the Saudi Building Code and the instructions of the competent authorities. For design and execution, use a licensed engineer or technician. Found an error? Tell us.