Contractors have a duty to point out any unsafe design flaws they find
The recent decision of the Court of Appeal in Plant Construction plc v Clive Adam Associates and Another for the first time ruled on a contractor's obligation to point out design faults of which the contractor is aware and which are dangerous.

The works involved the installation of two engine mount rigs in pits at Ford's research and engineering centre at Laiton, Essex. The substructure works were subcontracted by Plant to JMH Construction Services. The subcontractor was concerned about the adequacy of the scheme, although ultimately JMH followed the design provided by the structural engineer Clive Adams Associates.

During the installation works, it was necessary for the concrete base of one of the steel roof stanchions to be removed. Temporary support was provided by four props installed vertically between the underside of the floor and the steel roof trusses.

The roof collapsed one night during heavy rain, causing considerable structural damage and disruption. Plant paid damages to Ford and commenced proceedings against JMH and Adams.

Plant's case against JMH

Plant argued that JMH knew that the subcontract works were unsatisfactory, and that it should have been warned of the risks that existed. It was not denied that JMH had carried out the works in accordance with their instructions.

The Court of Appeal decided the case on interpretation of the implied contractual terms. Lord Justice May explained: "Subject to express terms, there will normally be an implied term that the contractor will perform his contract with the skill and care of an ordinarily competent contractor." On the facts of this case, JMH knew that the design of the temporary works was defective, and JMH "could have protested more vigorously". A further separate hearing was held before the original trial judge, Judge Hicks QC, to determine what would have happened had JMH protested in this way. It was held that either a new and safe design would have been produced, or that JMH would have refused to execute the unsafe design.

What would happen if the contractor did not know, but should have known, that the design was danger-ous? Or where there was a design defect, of which the contractor knew or ought to have known, which was not dangerous? It is clear that contractors who notice potential dangers in design detail should either: voice their concerns at the earliest possible opportunity; or ultimately refuse to execute the works. Commercially, this an onerous burden, particularly having tendered for works on tight profit margins. Equally, such assertiveness on the part of the contractor will hardly endear him to the site owner and/or consulting engineer in circumstances where the contractor's convictions are ultimately unfounded.

Accidental design responsibility

Matters become even more difficult for a contractor when they take the view that the design provided for them by others is not dangerous but it is clearly defective. Contractors are particularly skilled at taking on design responsibility almost by accident.

The first, and perhaps more common scenario is where it becomes apparent that matters cannot be progressed without immediate design input on site. It is often the experience of the contractor in combination with the technical expertise of the professionals involved on the contract that leads to a resolution of such a problem. But who is then responsible for such design?

Request a designer's instruction

Assuming a more traditional building contract relationship it must be prudent for the contractor to request the architect or supervising officer to issue a formal instruction to avoid arguments at a later date as to his responsibility for input. If there is a disagreement between the contractor and the architect over the method of design then it is clearly sensible for the contractor to voice its concerns in correspondence or by way of minute of meeting to avoid any potential comeback at a later date.

Another scenario can develop where the contractor plays a major part in pre-tender discussions in reviewing and revising the job including elements of design. This may well be the case even when the original tender package required no design input from the contractor.

It is quite easy for a contractor to find himself on the end of an order incorporating his own designs which were in no way intended to be anything other than an attempt to assist the employer and his design team in finalising what was perceived to be a cost effective development scheme.

Following the Plant case it is clear that contractors noticing dangers in design should place their concerns on record at the earliest opportunity. Also, insofar as voluntary design contribution, it is important to ensure that the contractor is only responsible in law for workmanship and not design. There is no doubt that contractors should voice their concerns, but when to voice them in public and when to voice them in private is the dilemma.