Knowledge · Standards
What Is a Waterproofing Performance Specification?
How a performance specification enables competitive procurement and contractor accountability on commercial waterproofing projects.
Last updated 14 March 2026
Direct answer
A waterproofing performance specification is a technical document that defines the required performance outcomes for a building’s waterproofing system – the grade of protection, design parameters, environmental exposure conditions, contractor qualification requirements, quality assurance procedures and handover documentation – without prescribing specific proprietary products. It is the contractual document that enables competitive tendering, objective evaluation and clear accountability for waterproofing performance on commercial developments.
Full explanation
The performance specification is arguably the single most important document in the waterproofing procurement process on a commercial development. It sits at the intersection of design and procurement, translating the waterproofing design philosophy into a contractually enforceable set of requirements that specialist contractors must satisfy.
Why performance rather than prescriptive?
A prescriptive specification names specific products and systems – for example, requiring a particular manufacturer’s sheet membrane, applied in a particular way. A performance specification instead defines what the waterproofing must achieve: the grade of protection required under BS 8102:2022, the design life, the environmental exposure parameters and the quality standards that must be met during installation.
The advantage of performance specification is threefold. First, it opens the competitive field – any specialist contractor who can demonstrate that their proposed system meets the stated performance requirements can tender, rather than limiting the field to those who work with a specific supplier. Second, it transfers the obligation to demonstrate compliance to the contractor, creating clear accountability. Third, it prevents the common situation where a supplier’s product specification is mistaken for a waterproofing design, which would result in the liability gap that generates so many disputes.
What a Performance Specification contains
A properly drafted waterproofing performance specification for a commercial development will typically address the following areas. The required grade of protection for each zone of the building, since different areas may require different grades, depending on their intended use. The environmental exposure conditions including groundwater levels, tidal variation, contamination and anticipated hydrostatic pressure. The design life requirement and the assumptions underpinning it. The minimum qualification requirements for the specialist contractor, including relevant trade body membership and installer accreditation. The quality assurance requirements during installation, including inspection hold points and testing regimes. The documentation required at handover, including as-built drawings, maintenance manuals and warranty terms. And the interface responsibilities – who is responsible for the junction between the waterproofing system and adjacent building elements such as the structural frame, drainage system and floor finishes.
Who should write it?
The performance specification should be written by an independent waterproofing design specialist appointed to the client’s design team – not by a product supplier, and not by the main contractor. The author must understand BS 8102:2022, the project-specific risk assessment, the design philosophy and the procurement strategy. They must also be independent of any product manufacturer or installation contractor, so that the specification genuinely serves the client’s interests rather than channelling work towards a preferred supplier.
The difference between a Performance Specification and a supplier design
This distinction is critical and widely misunderstood. Product suppliers routinely produce documents that resemble specifications – they reference British Standards, include performance data and contain detailed drawings. However, these documents are product recommendations, not performance specifications. They specify a particular manufacturer’s system and are designed to secure a supply order, not to define performance requirements for competitive tendering. Crucially, they almost always contain disclaimers excluding design liability. A performance specification written by an independent consultant carries professional design liability through the consultant’s professional indemnity insurance – a fundamentally different risk position for the client.
Frequently asked questions
Can a performance specification be used on a Design and Build contract?
Yes, and it is particularly valuable on D&B contracts. The performance specification can be included as an Employer’s Requirement, setting out the waterproofing performance standards that the contractor must achieve. This prevents the contractor from value-engineering the waterproofing to the lowest acceptable standard and provides the client with a contractual benchmark against which to assess the contractor’s proposed solution.
Does a performance specification add cost to the project?
The fee for producing a performance specification is typically a fraction of the waterproofing package value. The specification saves money by enabling genuine competitive tendering – without it, contractors price risk differently, scope varies between bids and the client has no objective basis for comparison. Projects without a performance specification routinely pay more for waterproofing because they cannot drive competitive tension or identify scope gaps in tenders.
What happens if a contractor cannot meet the performance specification?
If a tendering contractor cannot demonstrate that their proposed system meets the specified performance requirements, they are not qualified to tender for the work. This is a feature, not a problem – the performance specification filters out contractors who lack the technical capability or experience to deliver the required standard. The performance specification protects the client from appointing a contractor who would have struggled to deliver.
How detailed should a performance specification be?
Detailed enough to define the required outcomes unambiguously, but not so prescriptive that it limits innovation or unnecessarily constrains the contractor’s approach. The specification should define what must be achieved and how compliance will be demonstrated, while leaving the contractor free to propose the system and methodology that best achieves those outcomes. Getting this balance right requires specialist expertise – it is one of the core skills of an independent waterproofing consultant.
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