When to ask for a Single Joint Expert in a residential building dispute

What a Single Joint Expert is

Under CPR 35.7 the court may direct that expert evidence on an issue is given by one expert only, instructed jointly by the parties. The expert's duty is to the court (CPR 35.3), exactly as for a party-appointed expert, but the practical relationship is different. Each party may give instructions, copied to the other (CPR 35.8); the parties are jointly and severally liable for the fees unless the court orders otherwise; and either party may put written questions to the expert within 28 days of the report (CPR 35.6).

Practice Direction 35, paragraph 7, lists the factors the court weighs in deciding whether to direct a Single Joint Expert. They include whether the issue is within a substantially established area of knowledge, whether it is necessary for the court to sample a range of opinion, the amount in dispute, the importance of the issue to the parties, the complexity of the issue, and whether a party has already instructed an expert before proceedings began.

Why residential disputes suit the model

Most residential building disputes turn on a small number of valuation questions: what is the reasonable cost of putting right defective work, what is the value of the work left incomplete, what was the work actually done worth, and were the sums charged reasonable. These are questions of measurement and pricing, within an established area of knowledge, and the answers are rarely matters on which reasonable surveyors differ by a wide margin.

They are also disputes where the value at stake is modest. On the small claims track expert fees are capped at £750 per expert (CPR 27.14 and PD 27). On the fast track the court manages expert evidence tightly and will frequently direct a Single Joint Expert at allocation. Asking for one early signals proportionality and tends to be well received.

When not to ask

• Where causation is genuinely in dispute and depends on specialist diagnosis, for example structural movement or complex water ingress. A Single Joint Expert on cost may still be appropriate, with separate evidence on cause.
• Where one party has already obtained a detailed expert report pre-action and the other will not accept it. A fresh joint expert may be the fairest route, but the earlier report will be in the background.
• Where the amounts involved justify the cost of two experts and a joint statement, typically above the fast track limit and with real differences of approach.

Getting the instruction right

A Single Joint Expert can only answer the questions put. The joint letter of instruction is therefore the most important document in the process. From the expert's side, the letters that work share these features:

• Agreed questions, numbered. "What is the reasonable cost of remedying the defects listed in Schedule A?" is answerable. "Please comment on the works" is not.
• An agreed schedule of alleged defects or disputed items, even if the parties disagree about whether each is a defect. The expert reports against the list; the court decides liability.
• The contract and the pricing documents, or a statement that there are none, and the parties' positions on what was agreed.
• Access arrangements for inspection, including whether the contractor may attend.
• A realistic timetable that allows for inspection, any investigation that needs opening up, and the 28-day question period.
• Fee arrangements confirmed, including who pays what and when. Most Single Joint Experts will not start without the fee secured.

Where the parties cannot agree the letter, CPR 35.8 allows each to send separate instructions, copied to the other. That works, but it produces a longer report and a higher fee, because the expert must answer both sets.

What the report should give you

A good Single Joint Expert report in a residential dispute is short. It records the instructions, the documents, the inspection and the method, and then answers each numbered question with a figure, a basis and any assumption. Where an answer depends on a factual dispute the expert cannot resolve, for example whether a particular item was instructed, the report gives alternative figures on each assumption so the court can plug in its finding. Costs are built up from measured quantities and current rates, not round numbers, and the schedules are supplied in a form the parties can check.

After the report

Use the 28 days. Written questions under CPR 35.6 are the proper route to clarify or challenge; they are answered as part of the report and are usually the cheapest step in the whole process. In most residential disputes the report either produces a settlement within weeks or narrows the trial to one or two issues of fact. That is what it is for.

This article is general information for professionals and the public, not legal or professional advice, and does not create a client relationship. The law and procedure described are those of England and Wales as understood at the date of publication. Take advice on your own facts before acting.