A waterproofing specialist applies membranes, coatings and drainage systems to prevent water ingress through below-ground structures (basements, retaining walls) and flat roofs. Below-ground waterproofing in the UK is governed by BS 8102, which defines three types of protection - barrier, cavity drain and structural integral protection. Flat roof waterproofing is governed by BS 6229. Systems should carry BBA (British Board of Agrement) approval. The trade is not statutorily regulated but WIMLAS (Waterproofing Industry Manufacturers and Licenced Applicator Scheme) training and BBA-approved system installer status are key quality indicators.
What they do
- Apply cementitious and crystalline tanking systems to basement walls and floors
- Install cavity drain (Type C) membrane systems with drainage channels
- Apply external waterproofing membranes to below-ground structures
- Install EPDM, GRP, hot melt and built-up felt flat roof systems
- Waterproof podium decks, terraces and balconies
- Treat retaining walls and below-ground car parks
- Install green roof build-ups including root barrier and drainage layers
- Waterproof swimming pools and water features
- Diagnose and remedy leaking basements and flat roofs
When you need one
A waterproofing specialist is needed whenever water exclusion from a structure is critical - particularly for basements, flat roofs and below-ground elements.
Typical costs (UK, 2025)
| Job type | Typical cost |
|---|---|
| Internal basement tanking (per sq m) | £80 - £150 / sq m |
| External waterproofing membrane (per sq m) | £60 - £120 / sq m |
| Flat roof EPDM (supply + lay, per sq m) | £60 - £110 / sq m |
| Flat roof GRP (supply + lay, per sq m) | £70 - £130 / sq m |
| Podium deck waterproofing (per sq m) | £90 - £180 / sq m |
| Hourly rate | £45 - £75 / hr |
Costs are highly dependent on system specification, site access and substrate condition. Drainage, insulation and protection board are often priced separately. Always obtain quotes from BBA-approved system applicators and confirm the guarantee terms.
Qualifications to look for
British Board of Agrement (BBA) approved systems require installation by trained applicators. WIMLAS training covers the correct application of specific waterproofing systems. Always ask whether the contractor is approved by the system manufacturer as this is usually a condition of any guarantee.
The Certificate in Structural Waterproofing (CSSW) is the Property Care Association's qualification for basement waterproofing specialists. PCA member surveyors and contractors are held to a professional code and complaints procedure.
CSCS card expected on all commercial and larger residential projects. NVQ Level 2 in Waterproofing Occupations is the standard trade qualification. Some specialists also hold roofing NVQs covering flat roof systems.
How to find a reputable waterproofer
Frequently asked questions
What is the difference between tanking and cavity drain waterproofing?
Tanking is a waterproof barrier applied to the structure to keep water out. Cavity drain uses a studded membrane fixed to the wall with an air gap and drainage channel to manage water that enters. Both are valid approaches to BS 8102 - tanking is classified as Type A (barrier protection) and cavity drain as Type C (drained protection). The right choice depends on the water table, structure condition and how the space will be used.
What is EPDM?
EPDM stands for ethylene propylene diene monomer - a synthetic rubber membrane widely used for flat roofs. It is durable, flexible, can be welded seamlessly on larger roofs and carries a typical life expectancy of 50 years or more. EPDM is particularly well suited to large simple flat roof areas and is one of the most popular flat roof systems for domestic extensions.
How do I choose a flat roof system?
GRP (fibreglass) is best for complex shapes with upstands, gutters and detail work all formed in one material. EPDM suits large simple areas and is very durable. Built-up felt suits low-budget re-roofing where longevity is less critical. Hot melt (hot-applied rubber) is the premium choice for critical areas like podium decks and green roofs where zero tolerance for failure is required.