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Tank a basement or cellar.
Cavity drain or cementitious tanking — for habitable cellars, with sump and pump as needed.
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Wrong system for water condition
Type A tanking on active water ingress fails. Type C (drained cavity) is more reliable for water-prone basements.
Sump pump failure
Without battery backup, power cut causes flooding. Always specify dual-pump with battery.
Cheap tanking products
Generic cement coating fails. Use Vandex, Sika, Permagard.
Insurance challenges
Some insurers exclude basement contents. Check policy.
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
Type A tanking per m²Cement-based slurry
£40–£100/m²
Type C cavity drain per m²Membrane + drainage
£80–£180/m²
Sump pump installationIncluding backup battery
£800–£2.5k
Floor drainage channelPer metre
£40–£100
Internal plasterboard finishPer m² (over membrane)
£40–£80/m²
Small cellar (15 m²) Type AWalls and floor
£3.5k–£7.5k
!
Quote spread is typically ± 18% — always get 3 quotes.
At a glance
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Damp Proofer explained
Basements and cellars need waterproofing because they're below the water table. Expect to pay £4,500–£18,000 for UK basement waterproofing depending on system, size, and existing condition.
What Does the Work Invovle?
Three approaches per BS 8102. Type A (barrier): cement-based slurry (Vandex, Sika) painted on walls and floor. Suitable for stable, dry-ish below-ground. Type B (integral): waterproof concrete structure itself. New build only. Type C (drained cavity): dimpled HDPE membrane (Newton, Delta, Permagard) on walls behind plasterboard, with floor drain to a sump pump. Most reliable for active water ingress.
Typical Costs
| Item | Low (£) | High (£) | Notes |
|---|---|---|---|
| Type A tanking per m² | 40 | 100 | Cement-based slurry |
| Type C cavity drain per m² | 80 | 180 | Membrane + drainage |
| Sump pump installation | 800 | 2,500 | Including backup battery |
| Floor drainage channel | 40 | 100 | Per metre |
| Internal plasterboard finish | 40 | 80 | Per m² (over membrane) |
| Small cellar (15 m²) Type A | 3,500 | 7,500 | Walls and floor |
| Standard basement (30 m²) Type C | 9,000 | 18,000 | Premium system |
| Insurance-backed guarantee | 200 | 500 | 10–25 year cover |
How Long Does It Take?
Type A tanking: 1–2 weeks plus 2 weeks drying. Type C membrane: 2–4 weeks. Internal fit-out after: separate project.
DIY or Professional?
Professional only. PCA waterproofing specialist or CSSW-qualified contractor. Risk of failure is high; consequences severe (flooding).
Choosing the Right Tradesperson
PCA member with basement waterproofing certificate. CSSW (Certificated Surveyor in Structural Waterproofing) qualification. Insurance-backed guarantee mandatory (£200–£500 extra but essential). 10–25 year warranty.
UK Regulations
BS 8102:2022 code of practice for waterproofing below-ground structures. Building Regs Part C moisture control. Listed buildings need consent.
Common Problems
- Wrong system for water condition: Type A tanking on active water ingress fails. Type C (drained cavity) is more reliable for water-prone basements.
- Sump pump failure: Without battery backup, power cut causes flooding. Always specify dual-pump with battery.
- Cheap tanking products: Generic cement coating fails. Use Vandex, Sika, Permagard.
- Insurance challenges: Some insurers exclude basement contents. Check policy.
Frequently Asked Questions
Type A or Type C for my basement?
Type A (tanking) for occasional damp or stable conditions. Type C (cavity drain) for active water ingress. Quality surveyor specifies based on conditions.
How long does basement waterproofing last?
Type A tanking: 25–35 years. Type C membrane: 50+ years (it's a permanent system). Sump pumps need replacement at 8–15 years.
Do I need a sump pump?
For Type C systems: yes — the cavity drainage flows to a sump. For Type A: not usually. Always specify battery-backup pump for power cut protection.
Can I convert my cellar to a habitable room?
Yes — basement conversions add 15–20% to property value. Requires Building Regs notification (insulation, ventilation, escape).
Cellar musty smell — what's wrong?
Inadequate ventilation. Combined with subtle moisture ingress. Specify proper extract and waterproofing as a single project.
Insurance for waterproofing?
Insurance-backed guarantee (IBG) protects against contractor disappearance. Costs £200–£500 extra but covers 10–25 years. Essential — basement leaks cost £000s to fix.
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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