What Does the Building Safety Act Mean for Waterproofing Design? Competence Is Now a Legal Duty

Direct answer

Before the Building Safety Act, a design team that had not appointed a waterproofing specialist had a defence: BS 8102 is only a code of practice, and a code of practice cannot be broken. That defence is gone. Since 1 October 2023 the Act’s duty-holder regulations have required every person carrying out design work on a project regulated under the Building Regulations in England to be competent - to have the skills, knowledge, experience and behaviours the work demands - and required clients and Principal Designers to appoint only competent people. Waterproofing is design work. A basement waterproofing strategy produced by a structural engineer, an architect or a product supplier without waterproofing competence is no longer a departure from best practice. It is a breach of a statutory duty, and BS 8102:2022 is the yardstick that will be used to judge it.

Full explanation

The escape route the Act closed

For as long as I have been giving evidence in basement disputes, the same exchange has taken place. The claimant’s expert points out that no waterproofing specialist was appointed, as clause 4.2 of BS 8102 says one should be. The defendant’s side replies that BS 8102 is a code of practice, that a code of practice is guidance, and that departing from guidance is not negligence. It was never a strong answer - the standard is written into contracts, warranty requirements and the reasonable-skill-and-care test - but it was an answer.

The Building Safety Act 2022 did not mention waterproofing. It did something more useful. Through Part 2A of the Building Regulations 2010, in force from October 2023, it created a legal framework of duty holders - client, Principal Designer, Principal Contractor, designers and contractors - and imposed on every one of them a duty of competence. The question is no longer whether the design team followed a code of practice. It is whether the person who made the waterproofing decisions was competent to make them. If they were not, the code-of-practice point does not arise.

Competence has a definition now

The regulations define competence in four words: skills, knowledge, experience and behaviours. The industry shorthand is SKEB, and it is worth taking each word seriously in the waterproofing context.

Skills - the ability to carry out the waterproofing design: risk assessment to BS 8102, grade selection, system selection, detailing, the interface with structure, drainage and ground gas. Knowledge - the qualifications behind those skills; in this discipline, the Certificated Surveyor in Structural Waterproofing (CSSW) as the recognised minimum and the Property Care Association’s peer-reviewed Waterproofing Design Specialist register for complex and commercial work. Experience - of this building type, this depth, this ground and this procurement route, not of basements in general. Behaviours - and this is the word that matters most for waterproofing, because it is the one that removes the product supplier from the frame.

A supplier’s technical department can hold real skill and real knowledge. What it cannot hold is the behaviours of a designer, because its people are employed and rewarded to sell a system. A design produced under that incentive is not a design; it is a product catalogue applied to a site. The true cost of free waterproofing design has always been that the risk lands on the professional who accepted it. The Act adds a second cost: the professional has also failed a statutory competence duty by accepting it.

Three duties, and who fails them

The Act spreads the competence duty across the team, which is why it cannot be pushed onto a single party.

The client must make suitable arrangements for the work and take all reasonable steps to appoint people who are competent. A client who has not appointed a waterproofing designer at all has not discharged that duty for the waterproofing.

The Principal Designer must plan, manage and monitor the design work and co-ordinate matters relating to design, and must be satisfied that those carrying out design are competent. A Principal Designer who has allowed the waterproofing strategy to be settled “by the design team” - with nobody owning it - has not co-ordinated it; they have declined to.

Each designer must not accept design work they are not competent to carry out, and must not start it until satisfied the client is aware of the client’s own duties. A structural engineer who writes “Grade 3 protection will be provided to the full building envelope” into a Stage 3 report has accepted waterproofing design work. Whether they were competent to accept it is now a legal question.

None of these duties reaches a product supplier who was never appointed. The supplier is not a duty holder. Their specification, however thick, does not satisfy any of the three duties above, and their liability runs no further than a supply contract with the contractor. The chain of competence has a gap in it exactly where the waterproofing sits - which is also, in my experience, exactly where the water comes in.

The professional codes were already there

The Act did not invent the obligation to work within your competence. The codes of conduct of the Institution of Structural Engineers, the Institution of Civil Engineers, the RIBA, the Architects Registration Board and the RICS each require their members to undertake only work they are competent to perform. What the Act did was convert a disciplinary matter into a regulatory one, enforceable outside the profession. An engineer or architect who takes on the waterproofing design because it seemed simpler than appointing someone now answers to their institution and to the regulator, and their professional indemnity insurer will want to know why they were working outside the competence declared on their proposal form. The safer position - and the one BS 8102 has always pointed to - is an appointed waterproofing specialist working alongside them, with a defined scope and accepted liability.

Higher-risk buildings: gateways and the golden thread

For higher-risk buildings - residential buildings of at least 18 metres or seven storeys - the Act adds the Building Safety Regulator, the three Gateways and the golden thread. Gateway 2 requires the full design, including below-ground waterproofing, to be approved before construction starts, and controlled changes thereafter. The golden thread requires a continuous, accessible record of how the building was designed, built and is to be maintained.

Waterproofing is unusually exposed here because it is concealed. Once the slab is poured over the membrane, nobody can inspect it. If the golden thread does not contain the risk assessment, the design philosophy, the specification, the tender evaluation, the installation records and the as-built details, the waterproofing was not designed in any sense the regulator will recognise. Those records exist only if a competent designer was appointed early, produced documented outputs and monitored the construction. A product data sheet and a contractor’s programme are not a golden thread.

Longer to be found out

The Act also extended the limitation period for claims under the Defective Premises Act 1972: from six years to fifteen years for dwellings completed after 28 June 2022, and to thirty years retrospectively for those completed before. Basement waterproofing defects are slow. Ground water finds the weak joint in year seven, the blocked cavity drain in year ten, the membrane damaged during backfill in year twelve. Under the old six-year limit many of those claims died before they could be brought. They no longer do. The party who accepted the waterproofing design work - or who should have been appointed to it and was not - is within reach for far longer, and the first document a claimant’s expert asks for is the waterproofing appointment. When it does not exist, the case is already half made.

What this means on Monday morning

The Act does not require a waterproofing consultant by name. It requires competence, demonstrated and documented, and it requires the people who make appointments to check for it. In practice, on any project with a basement, a podium or a retaining wall, that means:

• a waterproofing specialist appointed under contract, before technical design, with a scope the Principal Designer can point to;
• competence evidenced - CSSW as a minimum, WDS registration for complex work, relevant project experience - and recorded in the appointment;
• design outputs that can stand in a golden thread: risk assessment, design philosophy, performance specification, monitoring records;
• and a Principal Designer who can show they co-ordinated the waterproofing rather than allowed it to be agreed.

The timing and scope of that appointment are set out in when to appoint a waterproofing consultant, and the wider allocation of responsibility in the waterproofing design responsibility matrix. To test where a specific project stands against the Act’s competence duty, put the design team and stage to the Waterproofing Wisdom agent, CLW’s specialist AI.