Damp is one of the most common defects found in older London properties, and one of the most frequently misdiagnosed. Treating the wrong type of damp with the wrong solution wastes money and can make the problem worse. Understanding the different types of damp and their appropriate treatments is essential before any remediation work begins.
Rising damp occurs when moisture from the ground rises up through the porous masonry of a wall by capillary action. In a properly built modern house, a damp proof course prevents this from happening. In many older properties, the original damp proof course has failed or was never present, allowing moisture to rise. Rising damp typically shows as a tide mark of salts and discolouration on walls up to about one metre from floor level. The correct treatment for genuine rising damp is the installation of a new damp proof course, either by chemical injection or by a physical slate or bituminous membrane, followed by replastering with specialist renovation plaster.
Penetrating damp is caused by water entering the building through the fabric from outside. Common causes include failed mortar joints in brickwork, blocked or broken gutters allowing water to run down the wall, failed window sills or cills, and roof defects. Penetrating damp typically shows in specific areas related to the source of the water entry. The correct treatment is to identify and repair the external defect first, then allow the wall to dry before replastering.
Condensation is the most common form of damp in occupied buildings but is often confused with penetrating damp or rising damp. Condensation occurs when warm moist air meets a cold surface, causing water to deposit on the surface. It is most common in bathrooms, kitchens, and bedrooms, particularly in poorly ventilated or poorly insulated buildings. The correct treatment is improved ventilation, adequate heating, and where possible improved insulation of cold surfaces. Chemical damp proofing is not the appropriate treatment for condensation.
Interstitial condensation is a more subtle problem that occurs within the fabric of a wall or roof when warm moist internal air meets a cold surface within the construction. This can lead to moisture damage to insulation, timber, and other materials within the building fabric. It is most commonly encountered in insulated flat roofs and walls where the vapour control layer is incorrectly detailed.
Before commissioning any damp treatment work, it is worth obtaining an independent survey from a qualified building surveyor rather than from a contractor who sells damp proofing solutions. A surveyor with no commercial interest in the outcome is more likely to give you an accurate diagnosis.
RCB Design and Build works with qualified building surveyors to diagnose damp correctly before we undertake any remediation as part of a refurbishment project.