How to Deal With Damp in a London Home
Damp is one of the most common building pathology problems in London's Victorian and Edwardian housing stock — and one of the most frequently misdiagnosed and inappropriately treated. Understanding the different types of damp, how to identify which type you're dealing with, and what the appropriate remedies are protects you from spending money on the wrong solution.
Types of Damp
Penetrating damp. Water entering the building through defects in the external fabric — failed pointing, damaged roof coverings, blocked or overflowing gutters, cracked render, or failed window seals. Penetrating damp is almost always the result of a specific building defect that can be identified and fixed. The remedy is to fix the defect, not to treat the internal symptom.
Signs: damp patches that relate spatially to an external defect (below a parapet, adjacent to a window frame, at the base of a chimney stack, at roof level). Damp patches that worsen during or after rain.
Rising damp. Groundwater rising through the walls or floor by capillary action. Genuinely rising damp in a properly built wall with a functioning damp proof course (DPC) is relatively rare in London — but in older Victorian properties without a DPC, or where the DPC has failed, rising damp does occur. True rising damp is typically confined to the lower 1–1.2 metres of a wall.
Signs: damp patches in the lower section of ground-floor walls, often with salting (white mineral deposits) as moisture evaporates from the wall face. Damp that doesn't relate to an obvious external defect or to condensation sources.
Condensation. The most common type of damp in London homes — and the most frequently misdiagnosed as penetrating or rising damp. Condensation occurs when moist warm air meets a cold surface, causing water vapour to condense. It's particularly prevalent in kitchens, bathrooms, and north-facing rooms with cold external walls and limited ventilation.
Signs: black mould on cold surfaces, particularly in corners, behind furniture, on north-facing walls, around windows, and in poorly ventilated spaces. Condensation on windows. Musty smell.
The Right Remedy for Each Type
Penetrating damp: Fix the external defect. Repoint, repair the roof, clear gutters, reseal windows. Once the water ingress is stopped, the wall will dry out over weeks or months.
Rising damp: Remedial DPC installation (chemical injection or electro-osmotic systems) combined with tanking or re-plastering with sand and cement mix to below damp height. Address any bridging of the DPC by ground levels or external renders.
Condensation: Improve ventilation (mechanical extract ventilation in kitchens and bathrooms, background ventilation throughout); improve insulation on cold surfaces (to reduce the incidence of cold spots below the dew point); reduce moisture production (cover pans, dry clothes outside or with a vented dryer, use extractor fans).
If you're not sure which type of damp you're dealing with, commission an independent damp survey from a RICS-registered building surveyor or a specialist damp surveyor — not from a damp treatment company, who have a financial incentive to recommend treatment regardless of the cause.
07359 872594 | contact@rcbgroup.co.uk | www.rcbgroup.co.uk