Is there a duty to warn?


Building contracts typically address the allocation of design responsibility upfront, i.e. is it borne by the employer or passed to the contractor/subcontractor? However, even when the contractor/subcontractor has no express design responsibility, there is case law confirming that, in certain circumstances, there may be a duty to warn the employer/contractor of the inadequacies of another's design. In what circumstances does such an obligation arise? If a duty to warn exists, what must the contractor/subcontractor do to discharge this obligation?

When a duty arises

The leading case is the Court of Appeal decision in Plant Construction plc v Clive Adams Associates & Anr (2000). Plant was successfully sued by Ford following a roof collapse in the course of construction due to a failure in the temporary works of Plant's subcontractor, JMH. The position of the roof propping, which had been directed by Ford's engineers, Clive Adams, was found to be the cause of the failure. Plant then sought to recover its losses from JMH and Clive Adams.

Normally a contractor or subcontractor will be responsible for the design of any temporary works they undertake. In this case, however, Clive Adams had directed the location of the propping and JMH's subcontract had been varied to the effect that they were to follow Clive Adams' instructions, so the design liability relative to the temporary works was taken out of JMH's hands and JMH escaped liability - or so it thought.

The Court of Appeal decided that although the subcontractor here was not responsible for the design of the temporary works, they were under an obligation to perform the contract with the skill and care of an ordinarily competent contractor and this included an obligation to warn of the danger they had seen. The fact that others were responsible and at fault did not mean that the subcontractor was not under a contractual obligation to warn of a danger.

The slightly later decision in Aurum Investments Ltd v Avonforce Ltd (2000) emphasised that it must be reasonable to impose a duty to warn in the circumstances. Here the subcontractor carried out underpinning work in the basement. The contractor claimed that the subcontractor owed a duty to warn them of the need to provide lateral support during the contractor's excavation works. The judge held that it would be unreasonable to do so. It was fatal to the contractor's case that the subcontractor did not know how the excavation works were to be carried out, nor was there any reason for the subcontractor to suppose that the contractor would carry out his work in a dangerous manner or negligently, especially as the subcontractor knew that the contractor was being advised by an apparently competent engineer. If the subcontractor had been aware of the contractor's proposals and said working, he might well have found himself liable for a proportion of the loss.

Discharging that duty

So if a duty to warn is implied, what must the contractor or subcontractor do to discharge this? Depending on the nature of the defect, it may not be enough merely to warn the employer or designer of the danger. In Plant Construction, JMH had warned of the problems but were still found to be in breach – why? Because in the court's view JMH hadn't protested vigorously enough! The court considered that JMH's objections should have been more insistent and that, as a last resort, JMH should have refused to carry out its works.

Key points

If a contractor/subcontractor is aware or ought to be aware that the proposed works designed by others are likely to pose a danger, there may well be an implied duty to warn of that danger.
In simple terms, the test is whether it is reasonable in all the circumstances to imply a duty to warn.

Where such an implied term exists the warning must be made "vigorously".

This article first appeared in Construction News in July 2012.