Design-and-Build Won't Transfer the Waterproofing Risk You Think It Does

Direct answer

Design-and-build does not make the waterproofing risk vanish — it changes who gets sued. Under D&B the contractor carries design responsibility, so if the basement leaks the client pursues the contractor rather than the designer directly. But that liability does not stop there: the contractor passes it down to the sub-contractor or supplier who actually produced the design, and so on down the chain to whoever got it wrong. The risk has not been transferred out of existence; it has been made to flow, and it flows back to the weakest, most-incentivised-to-cut-corners party in the chain. If that party has dissolved or cannot pay, the loss lands back with the client who thought it had been transferred away.

Full explanation

There is a comfortable belief, held by many architects and project managers, that procuring a basement under design-and-build solves the waterproofing problem by handing it, design and all, to a single accountable contractor. It is half true, and the half that is false is expensive. D&B is a contractual mechanism for allocating responsibility. It is not a mechanism for making a difficult engineering problem easy, and it does nothing to guarantee the design is any good.

What D&B actually moves

What D&B genuinely changes is the contractual route of recourse. In a traditional appointment the designer is liable to the client for the design; under D&B the contractor takes on the design obligation, so the client’s contract is with the contractor for both the design and the build. This is a real benefit — single-point responsibility and buildability under one roof. But “the contractor is responsible” is a statement about who you sue, not about whether the basement stays dry. The contractor will, in turn, have passed the design down to a waterproofing supplier or sub-contractor, often the same party offering a “free” design, and that is where the true cost of free design reappears — now buried two contracts deep.

The risk flows down, and down chains break

Liability under D&B behaves like water: it finds the lowest point. A leak triggers a claim against the contractor, who claims against the sub-contractor, who claims against the supplier whose design or product failed. This works cleanly only if every link in the chain is solvent, insured and still trading when the defect surfaces — often years later. Waterproofing defects are slow. By the time water appears, the specialist sub-contractor may have dissolved, the warranty may be worthless, and the professional indemnity behind the design may never have existed in the first place. When the chain breaks, the risk does not evaporate — it lands back on the building owner, who is left holding a defect that the contractual structure was supposed to have exported.

The thing D&B does not replace

The deeper error is believing that because the contractor will design it, the client side no longer needs to define what good looks like. A D&B contractor designs to the brief and the budget it is handed. Give it a vague brief and a keen number, and it will produce a vague, marginal design — entirely within its rights, because nobody told it otherwise. The control is to define the outcome before the package is let: the BS 8102 grade for each space and a product-neutral performance specification, written by an independent waterproofing designer on the client side. That converts the employer’s requirements into something you can enforce, and it means the contractor is designing to a competent standard rather than inventing one.

Novation is not independence

A common refinement is to novate the waterproofing designer to the contractor. Sometimes sensible, but be clear-eyed: once the designer answers to the contractor, their incentives migrate toward the contractor’s cost position, and the risks of placing waterproofing in the wrong scope return through a different door. Retaining a client-side waterproofing adviser alongside any novated team keeps one person accountable to the building rather than the margin. That is what actually protects the asset — not the procurement label on the front of the contract.

Wondering whether your D&B package really transfers the risk? Put your scheme and your draft employer’s requirements to the Waterproofing Wisdom agent, CLW’s specialist AI trained on BS 8102:2022.