Who Should Design Waterproofing on a Commercial Development?

Direct answer

Waterproofing on a commercial development should be designed by a qualified, independent waterproofing design specialist – not by the structural engineer, the architect, or a product supplier. BS 8102:2022, the British Standard for protection of below-ground structures against water ingress, requires that a suitably qualified person leads the waterproofing design, and the most robust way to satisfy this requirement is to appoint a specialist who holds a recognised credential such as the Waterproofing Design Specialist registration administered by the Property Care Association.

Full explanation

The question of who should design waterproofing on a commercial development is one of the most consequential decisions a client or project manager will make – and one of the most frequently mishandled. On the majority of commercial basement schemes in the UK, waterproofing design responsibility is never formally allocated to anyone. It falls into a gap between the architect, the structural engineer and the main contractor, with each party assuming another has it covered. The result is that waterproofing design often defaults to a product supplier –  providing a specification document that looks authoritative but carries no professional design liability.

Why not the structural engineer?

Structural engineers are experts in load paths, reinforcement design and structural stability. They are not, as a rule, trained in waterproofing risk assessment, system selection, or the interpretation of BS 8102. A Chartered Structural Engineer qualification does not include meaningful coverage of waterproofing design, and most engineering consultancies do not employ staff with the Certificate in Structural Waterproofing (CSSW). or WDS registration.

This matters in practice. Expert witness cases consistently reveal that when structural engineers take on waterproofing design – typically because it appeared to sit within their scope – the resulting designs exhibit poor risk assessment, inadequate grade specification and a fundamental misunderstanding of hydraulic gradient. One widely reported case involved a structural engineer from a major international consultancy who designed water bar details for a culvert project. The detailing failed to account for air entrapment during concrete curing when the water bar was inverted over the top of the structure – an error that any experienced waterproofing designer would have identified immediately. The financial consequences were severe.

Why not the architect?

Architects manage the overall design co-ordination and are responsible for the building’s performance as a whole. However, waterproofing design requires specialist knowledge of ground conditions, hydrostatic pressure, system compatibility, and long-term durability that falls outside architectural training. On most commercial developments, the architect is best placed to identify the need for a waterproofing specialist and advocate for their early appointment – not to carry the design responsibility themselves.

Why not a product supplier?

This is the most insidious gap in current industry practice. Product suppliers routinely provide documents that run to forty or more pages, include extensive reference to BS 8102, contain BBA certificates and feature detailed junction drawings. These documents have the appearance of a waterproofing design. However, they almost invariably contain a disclaimer – sometimes buried deep within the text –  stating that the document does not constitute a waterproofing design and that the supplier does not accept the role of waterproofing designer.

The contractual consequence is significant. The supplier’s contract is with the contractor, not the client. It is a supply contract, not a design contract. If the waterproofing fails, the client and the design team have no contractual recourse against the party that produced the document that everyone relied upon as the waterproofing design. As one industry commentator put it: make sure your waterproofing design is actually a waterproofing design before you rely on it as one.

Who should do it?

The waterproofing design should be led by an independent waterproofing specialist who is appointed directly to the client’s design team, with a clear scope of service and professional indemnity insurance that covers waterproofing design. This specialist should hold, as a minimum, the CSSW qualification, and ideally be registered on the PCA’s Waterproofing Design Specialist register – a credential that requires peer review of completed project work beyond the baseline qualification.

Independence is critical. A waterproofing designer who is employed by, or affiliated with a product manufacturer or installation contractor, cannot provide impartial system selection. Their recommendations will inevitably favour their own products or installation capabilities, regardless of whether those represent the optimum solution for the specific project conditions. An independent consultant has no commercial interest in any particular product or contractor and can therefore specify the system that best serves the building’s long-term performance.

On a commercial development, the waterproofing designer should be appointed no later than RIBA Stage 2, so that the design philosophy – the strategic framework governing waterproofing approach, risk assessment, and system selection – is established before the cost plan hardens and before detailed design decisions are locked in.

What BS 8102:2022 actually requires

BS 8102:2022 sets out requirements for design team composition in Clause 4. It requires that the waterproofing design is led by a person with appropriate qualifications, experience, and competence. The standard does not name a specific profession or credential, but it is clear that the designer must have specialist knowledge of waterproofing systems, risk assessment methodology, and construction detailing. The standard also requires a formal risk study (Clause 11), a documented design philosophy, and consideration of the building’s intended use, design life, and maintenance strategy – none of which can be adequately addressed by a party whose primary expertise lies elsewhere.