What Does the Building Safety Act Mean for Waterproofing Design on Commercial Developments?

Direct answer

The Building Safety Act 2022 significantly increases accountability for building envelope performance on higher-risk buildings in England, and its principles are reshaping expectations across all commercial development. For waterproofing design, the Act’s key implications are threefold: duty holders must demonstrate competence in their appointed roles, design decisions must be documented and traceable through a golden thread of building information, and those responsible for design elements – including waterproofing – face longer liability exposure under the extended limitation periods. The practical consequence is that leaving waterproofing design to a product supplier who disclaims design responsibility is no longer a defensible position.

Full explanation

The Building Safety Act 2022 was introduced in response to the Grenfell Tower disaster and the recommendations of Dame Judith Hackitt’s Independent Review. While the Act’s initial focus is on higher-risk buildings – defined as residential buildings at least 18 metres in height or with at least seven storeys – its principles of competence, accountability and traceability are influencing practice across the entire commercial construction sector. Waterproofing design, which has historically operated in a grey area of undefined responsibility, is directly affected.

The competence requirement

The Act establishes a framework of duty holders – the Client, the Principal Designer, and the Principal Contractor – each of whom must be competent to fulfil their role, and must ensure that the people they appoint to carry out design and construction work are also competent. This is not a vague aspiration. The Building Safety Regulator expects to see evidence of competence through qualifications, experience and organisational capability.

For waterproofing design, the competence requirement has a specific and practical implication. If the waterproofing design is being prepared by a product supplier’s technical department rather than by an appointed independent waterproofing designer with a clear scope of service and demonstrable competence, the duty holder chain is broken. The supplier is not a duty holder. They do not owe duties under the Act. And their specification document, however detailed it appears, does not satisfy the requirement for a competent person to have led the waterproofing design.

The most reliable way to satisfy the competence requirement for waterproofing is to appoint an independent waterproofing consultant who holds recognised credentials – the CSSW qualification and ideally registration on the PCA’s Waterproofing Design Specialist (WDS) register – and who is appointed with a clear scope of service under the client’s design team.

The golden thread

The golden thread is the Act’s requirement for a continuous, accessible and up-to-date record of building information that allows anyone involved in the building’s lifecycle to understand how design decisions were made, what was built, and how the building should be maintained. For higher-risk buildings, this is a statutory requirement. For all commercial developments, it is rapidly becoming a standard of good practice.

Waterproofing design is particularly sensitive in the golden thread context because it involves concealed elements. Once a basement slab is poured over a membrane, the waterproofing cannot be inspected without destructive investigation. The golden thread must therefore contain a complete record of the waterproofing design rationale, the risk assessment, the specification, the tender evaluation, the installation records and the as-built details. This record can only exist if a designer was appointed at early stage, produced documented outputs, and supervised the construction.

When waterproofing design defaults to a supplier specification with no formal design appointment, there is no golden thread. There is a product data sheet, a contractor’s programme and a gap where the design record should be. Forty years later, when the building owner needs to understand why water is entering the basement, there is no record of who decided what system to use, why, or how it was intended to perform.

Extended limitation periods

The Building Safety Act extended the limitation period for claims under the Defective Premises Act 1972 from six years to fifteen years for prospective claims (buildings completed after 28 June 2022) and introduced a retrospective thirty-year period for existing buildings. This is a fundamental shift in the risk landscape for waterproofing design.

Under the previous six-year limitation, many waterproofing defects only became apparent after the limitation period had expired, leaving building owners with no legal recourse. With a fifteen-year prospective limitation period, waterproofing defects that might previously have been discovered too late are now within the claims window. This means that those responsible for waterproofing design – or more precisely, those who should have been responsible but were never formally appointed – face significantly greater exposure.

For clients and developers, this changes the calculus of appointment. The cost of appointing an independent waterproofing designer at the outset is a known, bounded expense. The cost of defending a defective premises claim fifteen years later, without a design record, without a golden thread, and without a competent designer to stand behind the work, is unknowable and potentially catastrophic.

Implications for project teams

The Building Safety Act does not specifically mention waterproofing. It does not mandate the appointment of a waterproofing consultant. But it creates a regulatory environment in which the traditional approach – leaving waterproofing to the supply chain, relying on warranties, and hoping for the best – is increasingly difficult to defend. Principal Designers must demonstrate that every element of the building envelope was designed by a competent person. Clients must show that their duty holder appointments were adequate. And everyone involved in the project must contribute to a golden thread that records what was designed, who designed it, and why.

For waterproofing, this means formal appointment, documented design, traceable decisions, and independent oversight. These are precisely the outputs that an independent waterproofing consultant provides as standard.