Architects and the net contribution clause: what it does and why insurers like it

~5 min read

Reviewed by Matthew Bartlett, Director · Last reviewed 2026-07-06

The net contribution clause is one of the most consequential contractual devices in architectural practice. It sits in most standard architect appointment forms — the RIBA appointment documents, the ACA short form, the SFA/99 — and it modifies the architect's exposure in a way that meaningfully changes the risk carried by both the architect and the PII insurer. In broad terms, the clause caps the architect's liability to their just and equitable share of any loss where multiple parties are jointly responsible, rather than allowing the client to pursue the architect for the whole loss and leaving the architect to seek contribution from the other parties. This entry sets out what the clause does, why insurers require it in most appointments, and where it fails to bite.

The default position without a net contribution clause

Under English common law, where multiple defendants are jointly responsible for a loss, the claimant can pursue any one of them for the whole loss. The defendant sued then has a right of contribution against the other responsible parties under the Civil Liability (Contribution) Act 1978 — but that right of contribution is against the other parties, not against the claimant. If a contractor becomes insolvent, the architect who was jointly responsible for the loss can be pursued by the claimant for 100 per cent of the loss, with no realistic recovery against the insolvent contractor. The architect's PII policy responds — but the architect ends up paying (through the PII) for a share of the loss that fairly belongs to the contractor.

What the net contribution clause does

The clause changes this. It provides that, where multiple parties are jointly responsible for a loss, the architect's liability to the claimant is limited to the just and equitable share of the loss that would be apportioned to the architect on a fair contribution analysis. In effect, the clause shifts the contribution risk from the architect (who under the default position bears the risk that another responsible party cannot pay their share) to the claimant (who under the clause bears that risk). The clause does not affect the architect's liability for their own share; it only affects the exposure to picking up other parties' shares.

The clause typically operates as a contractual provision agreed between the architect and the client at appointment. It binds the client in contract but does not affect claims brought by third parties (tenants, subsequent purchasers, occupants) who are not parties to the appointment.

Why insurers want the clause

Architects' PII insurers strongly prefer appointments that contain a net contribution clause because the clause reduces the exposure the policy is asked to cover. On multi-consultant projects — most projects of any real size — the architect is one of several parties potentially responsible for any given loss: structural engineer, M&E engineer, contractor, subcontractors, cost consultant, client's employer's agent. If any of those parties becomes insolvent or is otherwise unreachable during the claim period, the net contribution clause is what stops the architect's PII being asked to pay for their share.

Some insurers require, as a condition of cover, that appointments contain a net contribution clause. Others accept the absence but load the premium accordingly. Practices that habitually sign appointments without net contribution clauses can face declines or materially higher rates at renewal.

Where the clause fails to bite

Three scenarios undermine the clause even where it is contractually present. First, third-party claims from parties who are not signatories to the appointment. A subsequent purchaser of a residential dwelling who brings a claim under section 1 of the Defective Premises Act 1972 (as extended by BSA 2022 s.135) is not party to the architect's original appointment with the developer client and is not bound by the net contribution clause. Second, where the client's appointment with the client is amended by side agreement or collateral warranty to displace the net contribution position — this can happen where the client's funder or a subsequent tenant requires the clause to be removed as a condition of accepting a collateral warranty. Third, where the appointment is silent on net contribution and default common law applies.

Building Safety Act 2022 exposures are particularly susceptible to the "third-party claim" gap. A dwelling built in 2015 with an architect's appointment containing a net contribution clause protects the architect against contribution risk on the developer's claim; it does not protect the architect against a 2028 claim brought by a subsequent purchaser who suffers loss because the dwelling is defective.

Drafting variations

Net contribution clauses vary in wording. The RIBA standard appointments contain a well-recognised clause. Bespoke appointments drafted by commercial clients often modify the clause — sometimes helpfully (extending it to explicit named parties), sometimes unhelpfully (narrowing it to specific types of loss or excluding certain circumstances). Architects reviewing a bespoke appointment should have the net contribution wording checked against their standard position; a broker or solicitor experienced in construction contracts can flag deviations.

Collateral warranties

Collateral warranties issued in favour of funders, purchasers or tenants often replicate or modify the primary appointment's net contribution position. A collateral warranty that omits the net contribution clause reintroduces the joint-and-several liability position for the warranted party — even where the primary appointment retained the clause. Architects issuing collateral warranties should ensure the warranty is drafted consistently with the primary appointment and should have the drafting reviewed at each material engagement.

Worked example

Illustrative only. A commercial fit-out project. The architect's appointment with the developer client contains a net contribution clause; the M&E engineer's appointment does the same. The contractor becomes insolvent midway through the works. The client sues both the architect and the M&E engineer for the whole loss. On a just and equitable contribution analysis, the architect's share is 25%, the M&E engineer's 20%, and the contractor's would have been 55%. Under the net contribution clauses, the client can recover 25% from the architect and 20% from the M&E engineer — and bears the 55% loss attributable to the insolvent contractor. Without the net contribution clauses, the architect and M&E engineer would have been jointly liable for the whole 100%, with a theoretical (but unrecoverable) claim against the insolvent contractor for 55%.