CLW design team working through RIBA stages

Process

Taking genuine responsibility for waterproofing.

From first-principle design through to contractor accountability on site. A process born from years of expert witness involvement in waterproofing failures.

By the numbers

The independence that makes the process work.

Registered WDS

BS 8102

Co-author

RIBA 2–7

Full stage coverage

Expert

Witness

Goldilocks Design.

We don't under-engineer. We don't over-specify. We develop waterproofing designs that are just right. Robust enough to perform for the lifetime of a building and efficient enough to avoid unnecessary cost.

Too Little

Weak design intent passed down the supply chain until nobody owns it.

Waterproofing design intent developed by non-specialists at RIBA Stage 2 gets pushed from contractor to sub-contractor. By the time anyone with expertise sees it, the cost plan is fixed and the scope for strategic input is minimal.

Just Right

Coordinated, specified, and owned. Driven by what the building needs.

CLW collaborate with the design team to develop the most robust waterproofing solution without adding unnecessary cost. Independent of any product manufacturer, we specify performance requirements. Not branded products.

Too Much

Supplier-led specifications biased toward over-specification.

Product suppliers are inherently biased toward specifying more material than the building requires. Their specifications are seldom coordinated with the structural design. Expensive, yet still may not deliver the required performance.

Don't know what Goldilocks design means? Find out here →

Best Value Procurement.

Why the industry norm leads to poor outcomes. And how CLW's approach changes the equation.

The industry norm is to have non-specialists develop a waterproofing design intent with input from a supplier. This weak design is issued in tender packs to main contractors, with the expectation that because it is design and build, all the risk lies with the main contractor. This leads to poor procurement through:

Hidden Risk Premiums. High risk percentages. Explicit from the main contractor AND more hidden from the supply chain. Inflate costs without improving quality.
Over-Specification and Over-Reliance. Over-reliance on waterproofing suppliers compounds additional material cost, install costs, and programme delays.
Non-Specialist Installation. You would never accept a plastering trade installing roof waterproofing. Why accept a blockwork trade installing structural waterproofing?

CLW develops a comprehensive waterproofing performance specification which allows for open tender amongst competent specialist structural waterproofing contractors who are free to select their preferred (and appropriate) waterproofing products. This open tender leads to more robust waterproofing and better value.

“I've worked closely with CLW on the Salisbury Square Development scheme, and they have shown outstanding value in picking up on issues early, guiding the design team and ensuring work on site complies with best practice.”

Jianxi Cheng · Director · Avison Young Salisbury Square

Contractor Accountability.

Independent oversight from design through construction.

A waterproofing design is only as good as its installation. Without independent oversight during construction, there is nobody on the client's side verifying that what is being installed matches what was specified, and nobody with the technical authority to challenge the contractor when it does not.

CLW remain appointed as client-side advisors throughout the construction phase. We carry out construction monitoring through regular site inspections at critical stages. Not to supervise the contractor's work, but to independently verify that the installation is consistent with the performance specification and design intent.

This accountability is only possible because CLW wrote the performance specification in the first place. A consultant brought in only for construction monitoring, working against a specification they did not write, cannot provide the same level of assurance.

The questions we hear most

Objections and how we respond.

Drawn from the conversations we have with developers, project managers, architects and contractors. The questions below are the ones that come up first, every time. Our answers are what we actually say when we are asked.

Question 01 If you don't specify the products, who does?

The competent specialist waterproofing contractor does, once they are appointed under the performance specification. That is the right place for product selection to sit: with the people who install the system, stand behind the workmanship, and carry the installation warranty. Our job is to define what the waterproofing has to achieve. Their job is to choose the products and details that deliver it. On high-risk buildings under the Gateway regime there are cases where some products do need to be named at design stage. On a more typical two-stage design and build, naming a Type C system and the parameters that govern it is enough. There is not a meaningful difference in outcome between membrane X and membrane Y if both meet the performance requirements.

Question 02 If final design responsibility rests with the specialist waterproofing contractor, why do we need you?

Because waterproofing design input is needed well before the specialist contractor is appointed. The decisions that drive cost and risk on a basement scheme are made at RIBA Stage 2 and 3, before tender. If those decisions come from a contractor, two things happen. First, they bake in their own product range. Second, they are not structured to deliver the level of design coordination across the architectural, structural and M&E packages that the scheme actually needs. By the time a specialist contractor sees the project, the structure has been designed, the grades have been assumed, and the cost plan is fixed. We sit upstream of all of that. We then continue to sit client-side once the contractor is appointed, supporting them in delivering the design rather than competing with them.

Question 03 Why don't we just go to the supplier for design advice?

Because suppliers do not normally hold design liability. Their technical literature is product literature: it tells you what the product can do under specific conditions, not whether the product is the right answer for your scheme. Suppliers do not normally give serious attention to the desktop study, the hydrogeology, or the coordination with the rest of the design team. They will bake in their own product. That bias is structural, not personal. A tender written against a supplier-led specification is a tender written against one supplier's product range, which limits competition and removes a significant lever for value.

Question 04 How can you write a comprehensive specification without naming products?

Because a performance specification defines outcomes. The grade of waterproofing required for each space, the hydrostatic case the system must resist, the construction joints and movement joints the system has to accommodate, the design life, the interface with the structural form. Those are the things that determine whether a basement will perform. A competent specialist waterproofing contractor reads a performance specification and proposes a system from their product range that meets it. The result is a tender that opens up competition among contractors against their preferred (and appropriate) products, rather than a tender locked to one supplier from the outset.

Question 05 Where does CLW's liability lie?

In the same place every other consultant's liability lies: in the scope of our contract. That scope is typically the outline waterproofing design, the determination of grade per space, the risk assessment, and the performance specification. On many schemes this is a highly developed RIBA Stage 3 or near-complete Stage 4 design. We are responsible for what we have designed, to the standard a competent waterproofing specialist would design it. CLW carries £10 million Professional Indemnity insurance. We are SSiP Approved Designers and Chartered Building Consultancy members. The liability position is documented and insured.

Question 06 Who holds responsibility where two suppliers' products meet at an interface?

The competent specialist waterproofing contractor procuring under the performance specification holds it. Junction and interface detailing, including the interface between two different products or between two different parts of the structure, is what specialist contractors are appointed to resolve. The hardest interfaces, podium to basement earth-retaining structure, blue roof to perimeter, lift pit to slab, are exactly where the performance specification is most prescriptive and where we tend to stay closest during construction monitoring.

Question 07 Surely the installer takes responsibility anyway. Why do we need you?

Once appointed, a competent specialist installer does take responsibility for the design they have agreed to install. But three problems remain if independent design has not happened upstream. First, the project does not get to the point of appointing a competent specialist without an independent design framework that defines what 'competent' looks like and what the tender is asking for. Second, the system selection question, whether the waterproofing system is right for the site, not whether it is correctly installed, is not something a contractor with a product range will answer impartially. Third, once the installer is on site, somebody on the client side needs to be able to challenge them on technical grounds when something departs from design intent. That client-side technical voice is what we provide. It is not adversarial. It is the thing that lets the installer focus on the work and lets the client sleep at night.

Question 08 What about value engineering pressure during the programme?

The cost plan gets squeezed. The QS looks for savings. The waterproofing package is visible and relatively easy to reduce. An independent consultant resists value engineering that reduces performance below what is required, because we have no commercial relationship with the supplier and no margin in the package. A contractor who is also the installer has a financial interest in margin and a relationship interest in keeping the project moving. Their resistance to value engineering is compromised from the start. That is not a criticism of contractors. It is a description of the position they are placed in.

Question 09 Who signs the waterproofing off at practical completion?

If the designer and the installer are the same party, sign-off is self-certification. The contractor is confirming that their own work meets a standard they set themselves. That is not accountability. It is the absence of it. Independent construction monitoring, by a consultant with no relationship to the installer, is the mechanism that creates genuine accountability. At PC the consultant signs off that the installation matches the design. That signature has meaning because it comes from an independent party. It supports the Building Safety Case, satisfies latent defect insurers, and gives the developer a defensible position.

If your question is not on the list, send it. We will answer it the same way we answer the rest. Plainly, in writing, with our name on it.

Ask a question →

RIBA Plan of Works

How we operate stage by stage.

Outline Design

Spatial Coordination. Waterproofing can and does have significant implications for design, e.g., on gross internal areas, threshold levels and more. Without competent waterproofing design at RIBA Stage 3, serious issues can develop later in the process that can be much more difficult and time-consuming to correct.

RIBA Stage 2-3

Detail Design

Technical Design. Waterproofing detailed design requires coordination with other disciplines. With our knowledge and experience, we are quick to understand the relevant issues, able to clearly communicate them to relevant stakeholders, and to work collaboratively with others to solve them. Our BIM2 capabilities allow us to work in Revit and Navisworks and extract section details in order to identify issues and provide solutions. We also offer clear, easy-to-understand waterproofing performance specification documents that help ensure you buy what you need.

RIBA Stage 4a

Procurement Advice

Client Side Advice. Our experience and standing enables us to give proper consideration to value engineering and alternative waterproofing proposals. We are also well placed to scrutinise the value propositions of various warranties and insurance offerings.

RIBA Stage 4b

Client Side Advisor

Manufacturing & Construction. During construction further waterproofing design development is likely to occur. We are able to vet design tweaks and ensure that waterproofing remains in line with the broader strategies developed. We then continue to add value through assessment of guarantees and other handover information.

RIBA Stage 5-6

In Use Advice

RIBA Stage 7 covers the building in use. We can advise on waterproofing performance in many circumstances, including defect investigation, dispute resolution and condition surveys.

RIBA Stage 7

“I worked with CLW on the 220 Blackfriars Road project and found their team to be very competent and professional. Their technical expertise on waterproofing design was valuable and allowed us to overcome some complex challenges.”

Miguel Bronze · Project Director · EPR Architects 220 Blackfriars Road

The CLW Service

Whole-building perspective. Direct client appointment.

Our preference is to be appointed directly by the client. Normally a developer or their project manager. From this position we work with the rest of the design team to understand waterproofing holistically, with a whole-building perspective.

We start by understanding the site: soil conditions, hydrogeological situation, risk of contaminants, and flood risk. We then establish the client's requirements. Intended use, finishes, sustainability objectives, and ventilation strategy. With that foundation, we shape the structural waterproofing.

We do not simply select product types and draw them on section details. We influence the design of the structure itself so that the whole situation is suited to the behaviour of water on each site, for the life of each building.

The result is a building where the waterproofing was designed by the right people, procured on the right terms, and built to the right standard. That is what genuine responsibility looks like.

Discuss Your Requirements.

Whether you are at RIBA Stage 2 or deep into construction, CLW can add value. Talk to us about your waterproofing challenges.

Contact CLW