The four specific clauses
| Clause | What it organises |
|---|---|
| Handling of discoveries | what happens when an unforeseen element appears |
| Variation process | how a variation is requested, priced and accepted |
| Regime for interruptions | who bears a stoppage and on what terms |
| Status of assumptions | what was assumed and what happens if it proves wrong |
Those four clauses answer the same question: who bears the gap between what was assumed and what is found.
None is necessary in new build, because the object there is fully defined before execution.
Why they are drafted beforehand
A chronological obviousness whose consequences are underestimated. The contract is signed before the existing fabric is fully known.
After a discovery, positions are fixed. The site is open, the programme is running, and the client has few alternatives.
Beforehand, both parties reason about an abstract situation, which allows a balanced agreement on a rule rather than on an amount.
A clause negotiated calmly protects both parties. The contractor knows how unforeseen work will be paid; the client knows they will decide before the work is carried out.
It is the only moment when a fair agreement is possible, and it takes a few minutes of drafting.
The status of assumptions
A little-used yet decisive clause, extending the bill of quantities. It organises the fate of discoveries.
A renovation quotation rests on assumptions, explicit or not, about the make-up and condition of the existing.
Writing them into the contract produces two effects. They become checkable, and their disproof becomes a contractual event rather than a matter for argument.
An unwritten assumption does not disappear. It resurfaces as disagreement, each party asserting in good faith what they had understood.
This connects with the article on measurement in renovation, which covers how to distinguish measured, assumed and conditional quantities. The uncertain items are covered there.
What these clauses avoid
Three concrete situations, frequent and costly. They arise once the fabric is opened up.
Works carried out with no price basis. Without a variation process, necessary remedial work is done and invoiced afterwards.
Unallocated stoppages. Without an interruption regime, a halted project generates costs nobody clearly bears.
Arguments about what was included. Without written assumptions, every gap becomes a question of interpreting the original quotation.
Those three situations end in the same place: negotiation mid-project, in an unbalanced position, over unanticipated amounts.
What remains of the general law
A useful clarification for situating these clauses. They supplement the contract without replacing the statutory rules.
They add to the clauses required of any construction contract, covered in the corresponding guide on the clauses that protect.
They cannot derogate from mandatory provisions. Where the act protecting purchasers applies, or in matters of ten-year liability, the contract cannot reduce statutory protection.
They therefore organise technical contingency, not liability. The distinction is worth restating to the client, who sometimes conflates the two.
The articles in this branch
The article on discovery clauses covers the handling of unforeseen elements. Their drafting is set out there.
The article on addenda and additional works covers the variation process. The procedure is explained there.
The article on periods and interruptions covers time and its allocation. The causes of suspension are listed there.
The article on developments to monitor lists the moving points of the applicable framework. The reforms under way are followed there.
This article sets out drafting principles at the date of checking and serves professional orientation. It does not constitute legal advice and does not replace assessment of the individual case.