Damp proofing cost by treatment type
Damp proofing cost in London by treatment category: Chemical DPC injection (rising damp — silicone cream injected into the base of the wall): £800–£2,500 per ground floor elevation (excluding replastering). Chemical injection including replastering (waterproof render to 1m height internally): £1,500–£4,000 per ground floor elevation. Electro-osmotic damp proof system (EOS — active electrical system): £1,500–£3,500 for a standard 3-bed terrace ground floor. Waterproof external coating (Kiesol C, Delta Thene — penetrating water repellent): £300–£800 per elevation. Silicone cream external injection (secondary DPC, for penetrating dampness through wall face): £600–£1,500 per elevation. Cavity drainage membrane system (Triton Newlath, Platon — for damp basement walls): £4,000–£10,000 for a typical London basement. Basement structural tanking (cementitious slurry — Sika 1, Vandex, Thoroseal): £8,000–£20,000 for a full basement waterproofing system. Verify all damp proof guarantees are backed by an insurance-backed guarantee (IBG) scheme (Property Care Association member contractors issue IBG guarantees).
Rising damp vs penetrating damp vs condensation — diagnosis matters
The correct diagnosis of damp type is essential before any remediation. Rising damp: groundwater rises through the capillary structure of the wall above the damp proof course. Characteristics: a tide mark at a consistent height (typically 0.5–1.5m above floor level); affected plaster is powdery and has white salt deposits (hygroscopic salts); moisture meter readings elevated consistently at the base of the wall. Note: true rising damp is rarer than commonly diagnosed — Victorian terraces often suffer from condensation or penetrating damp that presents similarly. Penetrating damp: rainwater enters through the wall face (eroded pointing, cracked render, failed window seals). Characteristics: moisture appears on inner face after rainfall; limited to one elevation; may be localised around a window. Treatment is external — repointing, re-rendering, or waterproof coating. Condensation: moisture condenses on cold wall surfaces. Characteristics: moisture appears on cold bridge surfaces; mould growth is common; typically worst in winter. Treatment is ventilation, insulation and heating — not a chemical DPC.
Independent damp survey vs damp-proofing company survey
The most important caveat in any damp investigation is the independence of the surveyor. Damp-proofing company surveys: free surveys offered by PCA member contractors and non-member companies alike. A contractor-employed surveyor has a commercial incentive to recommend treatment — the most common outcome is a recommendation for chemical DPC injection plus replastering, regardless of whether rising damp is the actual diagnosis. This generates a £1,500–£4,000 job ticket. Chemical DPC injection is frequently recommended in cases of condensation or penetrating damp where no rising damp exists. Independent damp survey: commission a RICS-qualified surveyor with damp investigation experience to diagnose the damp independently. An independent survey costs £200–£500 but can save £1,000–£3,000 in unnecessary treatment costs. A good independent survey will: take moisture readings at multiple heights and on multiple elevations; test for hygroscopic salt contamination; assess the external drainage, pointing and render condition; review ventilation. Builderr includes an independent damp assessment as part of the pre-renovation survey package on all projects where damp is identified.
Basement waterproofing in London
Basement damp proofing in London is a specialist field — London clay and the shallow water table create significant hydrostatic pressure on basement structures. The two principal approaches for existing basements: Type A (barrier waterproofing): cementitious tanking (Sika 1, Vandex, Thoroseal) applied to the internal face of the basement walls and floor — creates a rigid barrier against water ingress. Most cost-effective for basement walls with limited water pressure. Cost: £50–£80/m² of tanked area; full basement typically £4,000–£10,000. Type C (cavity drainage): a studded drainage membrane (Delta MS, Platon P8) is fixed to the internal face of the walls and floor, with a perimeter channel directing groundwater to a sump and pump system. Most appropriate for London basement conversions in areas of higher water table or significant hydrostatic pressure. Cost: £8,000–£20,000 for a standard London basement, including sump and pump system. Guarantee: a BS 8102-compliant waterproofing system specified by a Certificated Surveyor in Structural Waterproofing (CSSW) is the standard for any London basement waterproofing — insist on a CSSW-specified design and a 25-year IBG-backed guarantee.
