How to Price a Damp Proofing Job: Injection DPC, Tanking and Membranes

Quick Answer: Damp proofing pricing depends on diagnosis: rising damp injection DPC £80–£140 per linear m, basement/wet-room tanking £80–£180 per m², penetrating damp render-strip-and-replaster £45–£90 per m², penetrating damp external repair variable. Always start with a specialist damp survey (£250–£500) before quoting — the wrong diagnosis means the wrong fix and warranty implications. PCA-accredited contractors and 20-year insurance-backed guarantees cost 15–30% more but provide warranty cover that survives sale of the property.

Summary

Damp pricing is one of the most diagnosis-sensitive trades in UK construction. The same visible symptom — staining, blown plaster, peeling paint at low level — can result from rising damp, penetrating damp through external walls, condensation, leaking plumbing, or interstitial condensation in insulation systems. Each cause has a different fix at a different price point, and applying the wrong fix typically makes the problem worse over 12–24 months.

The standard UK approach: commission a damp survey (£250–£500), let the survey identify the cause, then quote the specific remediation. Don't quote on visual inspection — the customer pays you to fix the cause, not to apply a generic damp-proof treatment. The Property Care Association (PCA) Code of Practice and BS 6576:2005 (Code of practice for diagnosis of rising damp) provide the methodology framework.

In 2026, prices for traditional rising damp work have stabilised; basement tanking has climbed 10–15% as PCA standards have tightened; specialist membrane systems are now significantly more expensive than five years ago because of EPDM and similar input cost rises.

Key Facts

• Damp survey cost — £250–£500 typical; PCA-qualified surveyor preferred
• Injection DPC (rising damp) — £80–£140 per linear m supply-and-fit
• Re-plastering after DPC — £45–£90 per m² (sand-cement waterproof render + skim)
• Basement / wet room tanking — £80–£180 per m² (cementitious system); £120–£260 per m² (cavity drain membrane)
• Cavity drain membrane (Type C) — £80–£140 per m² for membrane only; £120–£260 per m² with sump and pump system
• Penetrating damp repair — variable, £450–£3,500 typical job
• External repointing for damp — £80–£160 per m² of wall area
• Lime mortar repointing — £130–£260 per m² (heritage)
• Insurance-backed guarantee — typically £200–£600 added to job; 10 or 20 year cover
• PCA membership — required for most insurance-backed guarantees
• Diagnostic tools — moisture meter (electrical resistance), Speedy carbide test, hygrometer, salts test

Quick Reference Table — Pricing by Damp Type

Detailed Guidance

Step 1: Diagnose, don't assume

The single most common mistake in damp work is treating the symptom without diagnosing the cause. Common misdiagnoses:

• Treating "rising damp" with injection DPC when the actual cause is hygroscopic salts from old chimney breast — DPC has no effect; problem persists
• Treating "penetrating damp" with external waterproofing when the cause is condensation — sealed wall makes condensation worse
• Treating "rising damp" with tanking system that traps existing moisture — water finds a different path
• Treating "condensation" as rising damp — applying impermeable plaster systems makes the problem worse

A proper damp survey:

1. Visual inspection — locate the affected area, photograph
2. Carbide test — drill 100mm into wall, take sample, measure water content with calcium-carbide reaction (Speedy meter)
3. Salts test — chloride and nitrate testing distinguishes rising damp (high salts) from condensation (low salts)
4. Hygrometer / RH measurement — 7-day data preferred for condensation diagnosis
5. External survey — pointing, render, lead detail, gutters, downpipes, flashing
6. Internal inspection — paint coverage, plaster patterns, ceiling staining

The combination of these gives a confident diagnosis. Single-point moisture meter readings are unreliable — they detect surface moisture from any cause.

Rising damp — the classic case

Rising damp is moisture rising up through brick and mortar by capillary action. It's a real phenomenon but over-diagnosed — a properly surveyed property finds rising damp in maybe 1 in 5 cases of low-level damp staining.

Symptoms:

• Damp at the base of internal walls, no higher than 1.0–1.2m from floor
• Tide line of damp staining
• White salts (efflorescence) on wall surface
• Plaster blown or detaching at low level
• Skirting boards rotting
• Carbide test showing high moisture content

Treatment:

1. Strip plaster to 300mm above damp tide line (typically 1.5m from floor)
2. Install chemical injection DPC (silicone or stearate at 100–150mm above ground level)
3. Re-plaster with waterproof sand-cement render (3:1 sand-cement with waterproofer + bonding additive) up to 1.0–1.2m
4. Skim with finishing plaster
5. Allow 4–6 weeks before redecorating

Typical cost: £100–£200 per linear m of treated wall.

Penetrating damp — the most variable

Penetrating damp is moisture entering through external walls, roof, or windows. The fix depends entirely on the entry point. Common scenarios:

• Defective pointing — repoint affected area, internal repair
• Cracked render — repair render, internal repair
• Failed lead flashing — replace lead, internal repair
• Defective DPC — repair DPC, internal repair (if DPC was the cause, not absence of DPC)
• Cracked rendering / spalled brick — replace brick or render, internal repair
• Failed window seal — re-seal, internal repair
• Defective gutters/downpipes — repair, internal repair

Pricing is wholly job-specific — there's no per-m² rate for penetrating damp. Always quote the diagnostic cause + specific fix + internal make-good as separate line items.

Tanking — basements and wet rooms

Tanking is waterproofing applied to retain water against the wall. Two main systems:

Type A (cementitious tanking). Multi-coat cement-based render with waterproofer, applied internally. Resists hydrostatic pressure. Standard for basements with Grade 1–2 protection requirement. Typical cost £80–£180 per m².

Type C (cavity drain membrane). Plastic membrane with studs creating a drainage cavity behind, water collected in perimeter channel and pumped to drain. Standard for basements with Grade 2–3 protection requirement (BS 8102:2022). Typical cost £120–£260 per m² with sump/pump.

For most domestic basement conversions, both Type A and Type C are used together (combined Type A + Type C system is standard for habitable basement under BS 8102:2022 Grade 3).

For wet rooms (Showers, bathrooms with continuous wet exposure), tanking systems differ:

• Self-adhesive tanking membrane with cementitious patch tape — £30–£60 per m² supply
• Liquid-applied tanking (Schluter, BAL, Mapei systems) — £25–£45 per m² supply
• All require specific install detail per wet area waterproofing guide

Insurance-backed guarantees

Insurance-backed guarantees (IBGs) are insurance policies that pay for re-treatment if the damp returns within the warranty period. Required by mortgage lenders for properties with treated damp (typically 10–20 year cover). Provided by:

• Property Care Association (PCA) — most common in UK
• Gpig (Guarantee Protection Insurance)
• Trustmark — wider remit including various trades
• BBA Approved Inspector — building-related certification

IBG typically adds £200–£600 to the cost of damp work but the cover survives sale of the property. For mortgage-supported sales, IBG is typically required.

PCA membership is the standard requirement — only PCA-accredited contractors can offer PCA-backed IBGs. Most reputable damp contractors are PCA-accredited.

Frequently Asked Questions

What's the cost of damp-proofing a UK 3-bed semi (homeowner-friendly)?

For a typical UK 3-bed semi with confirmed rising damp on 8m of wall: survey £300, injection DPC £900–£1,400, replaster £600–£1,200, decorate after settle £450, IBG £300. Total: £2,500–£3,650 in 2026. For penetrating damp, costs are widely variable — could be £400 for a single failed lead flashing or £4,000 for full external repointing of a corner. For basement/cellar tanking, £8,000–£25,000 for a typical conversion. Always commission a survey first.

Should I get a 20-year guarantee?

Yes if the property is going to be sold within 20 years and a mortgage will be involved. Without an IBG, mortgage lenders typically require a fresh damp survey and possible re-treatment when the property sells. With an IBG, the cover survives the sale and re-treatment risk passes to the insurer.

Can I do my own damp work?

Some yes, some no. Re-pointing, internal repair, condensation management — yes, with appropriate tools. Injection DPC, basement tanking, complex remediation — generally not. Insurance-backed guarantees are not available to non-PCA-members.

What about tide marks above 1.2m?

Generally not rising damp — capillary rise rarely exceeds 1.0–1.2m through brickwork. Higher tide marks usually indicate:

• Hygroscopic salts from chimney or fire — different fix
• Penetrating damp (e.g. failed flashing) — different fix
• Bridge across a DPC by adjacent earth or paving — different fix
• Below-floor moisture connected to upper levels — different fix

A high tide mark always warrants thorough diagnosis before treatment.

What's the typical timescale for a damp job?

Survey to diagnosis: 1–2 weeks. Replacement plaster cure to redecoration: 4–6 weeks. Total typical residential job from survey to "ready for use": 6–10 weeks. For a basement conversion with combined Type A + Type C: 8–16 weeks.

Regulations & Standards

• BS 6576:2005 — Code of practice for the diagnosis of rising damp in walls of buildings

• BS 8102:2022 — Code of practice for protection of below-ground structures against water from the ground

• BS 8000-15 — workmanship of plastering and damp-proofing in building

• PAS 2030:2019 — energy efficiency installation requirements

• PCA Code of Practice for damp proofing

• Building Regulations Part C (Site preparation and resistance to contaminants and moisture)

• Insurance Conduct of Business Sourcebook (ICOBS) — IBG providers

• Construction (Design and Management) Regulations 2015 — domestic project responsibilities

• Property Care Association (PCA) — damp specialist accreditation

• BSI — BS 6576 rising damp diagnosis

• BSI — BS 8102 below-ground structures

• HSE — Construction CDM 2015 domestic projects

• Building Research Establishment (BRE) — damp guidance

• specialist damp survey methodology — diagnostic step before quoting

• warm roof vs cold roof — adjacent moisture failure mode

• interstitial condensation in walls — hidden moisture from retrofit

• waterproofing wet areas before tiling — adjacent specialist waterproofing