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Treat condensation & mould.
Diagnose ventilation, insulation and heating — fix the root cause, not the dot on the wall.
✓ Updated May 2026✓ Free quotes✓ Vetted pros
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Top tips
Hiring a damp proofer, without the regret.
Four moves that separate a smooth job from a nightmare.
Painting over mould without treating
Mould returns within months. Always biocide-treat first.
Ventilation off when "cold"
Tenants turn off extractor in winter to save energy. Result: condensation. Continuous low-rate ventilation (dMEV) better.
Cheap PIV not whole-house
Cheap PIV in one room. Effective PIV is loft-mounted and ventilates whole house.
Misdiagnosis
Condensation often misdiagnosed as rising damp. Survey carefully — condensation is much cheaper to fix.
Costs & timeline
Know what it costs. Know when it ends.
Indicative UK ranges and what affects price.
Cost range
By job type
Inc. VAT · 2026
Source: NMT quotes
Source: NMT quotes
Mould treatment per areaBiocide + redecoration
£40–£250
Bathroom extractor (humidistat)Vent-Axia, Greenwood
£150–£400
Kitchen extractor (continuous)dMEV unit
£200–£500
PIV (positive input ventilation)Whole-house, loft-mounted
£500–£1.2k
MVHR full systemPremium, whole-house
£2.5k–£6.5k
Cold-bridge insulation per m²Internal insulation
£30–£80/m²
!
Quote spread is typically ± 18% — always get 3 quotes.
At a glance
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Damp Proofer explained
Condensation is the most common UK damp problem and the cause of most "black mould" complaints. The new Awaab's Law (2026) requires landlords to address it within strict timeframes. Expect to pay £80–£3,500 for UK condensation treatment depending on scope.
What Does the Work Involve?
Cause analysis: humidity sources (cooking, bathing, drying clothes), ventilation, insulation cold-bridges. Remediation: extractor fans in bathroom and kitchen (PIV, MEV or dMEV), positive input ventilation (PIV) for whole house, sometimes MVHR (mechanical ventilation with heat recovery) for premium properties. Address cold-bridges with insulation upgrade. Black mould treated with biocide (Polycell, HG, Ronseal Anti-Mould).
Typical Costs
| Item | Low (£) | High (£) | Notes |
|---|---|---|---|
| Mould treatment per area | 40 | 250 | Biocide + redecoration |
| Bathroom extractor (humidistat) | 150 | 400 | Vent-Axia, Greenwood |
| Kitchen extractor (continuous) | 200 | 500 | dMEV unit |
| PIV (positive input ventilation) | 500 | 1,200 | Whole-house, loft-mounted |
| MVHR full system | 2,500 | 6,500 | Premium, whole-house |
| Cold-bridge insulation per m² | 30 | 80 | Internal insulation |
| Damp survey | 120 | 400 | PCA-qualified |
| Anti-mould paint upgrade | +£40 | +£150 | Per room |
How Long Does It Take?
Bathroom extractor install: 2–4 hours. PIV install: half a day. MVHR: 3–5 days. Mould treatment + redecoration: 1–2 days per room.
DIY or Professional?
Mould treatment with biocide: DIY. Extractor fans: electrician (Part P certified). PIV and MVHR: specialist installers.
Choosing the Right Tradesperson
For condensation: ventilation specialist (Nuaire PIV approved, Vent-Axia trained). For underlying damp: PCA-qualified surveyor. For landlord work: insist on Awaab's Law compliant timescales.
UK Regulations
Awaab's Law 2026: landlords must address mould in social/private rented housing within strict timeframes (typically 7–14 days for serious cases). Building Regs Part F: minimum ventilation rates. Part L: thermal performance affects condensation.
Common Problems
- Painting over mould without treating: Mould returns within months. Always biocide-treat first.
- Ventilation off when "cold": Tenants turn off extractor in winter to save energy. Result: condensation. Continuous low-rate ventilation (dMEV) better.
- Cheap PIV not whole-house: Cheap PIV in one room. Effective PIV is loft-mounted and ventilates whole house.
- Misdiagnosis: Condensation often misdiagnosed as rising damp. Survey carefully — condensation is much cheaper to fix.
Frequently Asked Questions
How do I know if I have condensation?
Black mould on cold walls (especially north-facing, around windows), high humidity, water on windows in morning, mould in corners and behind furniture. Tide marks at low level are rising/penetrating damp, not condensation.
What's the difference between condensation and rising damp?
Condensation: cold-spot mould, top-down patterns. Rising damp: bottom-up tide marks, salt deposits. Penetrating damp: localised internal damp from external source. Easy to confuse — get diagnosis.
Will an extractor fan fix it?
Bathroom and kitchen extractors are essential. For whole-house, add PIV (positive input ventilation, £500–£1,200) or MVHR (£2,500–£6,500). Don't expect single bathroom fan to fix whole-house issue.
What's Awaab's Law?
UK 2026 legislation requiring landlords to address damp and mould within strict timeframes (typically 7–14 days for serious cases). Failure to comply can result in fines and tenant compensation.
Will anti-mould paint solve it permanently?
No — paint is a symptom-treater. The underlying ventilation or insulation issue must be fixed. Anti-mould paint slows re-appearance but doesn't prevent.
How much can I save on bills with proper ventilation?
Counterintuitively: improved ventilation can save money. Dry air heats more efficiently than damp air. MVHR can save 20–30% on heating in well-sealed homes.
This guide was written with AI assistance and is intended for general information only. Prices are estimates based on UK averages and may vary by region. Always get at least three quotes and consult a qualified professional before starting any work.
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