What Is a Variation?

Variations arise from a wide range of causes, and understanding where a particular variation came from often affects who bears the cost. Common triggers include:

• Client-instructed changes — the client or their consultant asks for a different finish, layout or fixture than originally specified.
• Latent site conditions — unforeseen ground conditions, hidden services or existing structure not visible or documented at tender stage.
• Design development and errors — drawings issued after the contract that clarify, correct or add to the original design.
• Regulatory or authority requirements — a council or certifier requirement that was not part of the original scope.
• Provisional sum and PC item reconciliation — the actual cost of an allowance differs from what was carried in the contract.

Good practice is to document every variation before the work proceeds: describe the change, quote a price, note any impact on the completion date, and get the client’s written approval. Most standard form contracts — and many bespoke ones — make this the required process, not just best practice; some go further and specify that a variation not raised or approved in the prescribed form and timeframe cannot be claimed at all.

A typical variation trail runs from a variation request or site instruction, to a priced variation quote, to written approval (or, on larger projects, a formal variation order), before the additional or altered work begins. Keeping that trail — even for small variations — protects both sides: the contractor has evidence to be paid, and the client has a clear record of what was agreed and why.

• Variation request or instruction — raised by either party, describing the proposed change.
• Priced variation quote — the cost and time impact, submitted for approval before work starts.
• Written approval or variation order — signed off by the client or their authorised representative.
• Variation register — a running log of every variation, its status and its cumulative effect on the contract sum.

Where a Bill of Quantities or schedule of rates already exists, a variation is normally priced first against those contracted rates — that is precisely why a BOQ keeps earning its keep long after the tender is won. Extra concrete is priced at the BOQ concrete rate, an added door at the BOQ door rate, and so on, which keeps the pricing consistent and hard to dispute.

Where no contract rate covers the item — a genuinely new scope of work — the parties agree a fair and reasonable rate, usually built up the same way the original estimate was: labour, materials, plant and a margin. Time impact is priced separately from cost impact; a variation can add cost with no time effect, add time with no cost effect (a delay caused by the client, for instance), or both together.

A variation does not automatically extend the completion date — the contract usually requires the contractor to show, and the client (or superintendent) to agree, that the change genuinely affects the critical path of the program. Added scope that can be absorbed within existing float may not justify any extension at all.

Where a variation does affect the program, the time adjustment is usually formalised as an extension of time alongside the priced variation, and — because most preliminaries are time-related — a variation that extends the program often carries a corresponding prelims adjustment too. Keeping variations, time impacts and prelims linked in one place avoids arguing the same delay three separate times.

Either party can originate a variation. A client (or their architect, superintendent or contract administrator) instructs a scope change; a contractor raises one in response to a site condition, a design clash or an ambiguity in the documents. What differs is who ultimately has to sign off — most contracts nominate a specific approver, whether that is the client directly, a superintendent, or a project manager acting under a defined delegation of authority.

On larger and public-sector projects, variations above a threshold value are frequently escalated for a second sign-off, and a running variation register is maintained so everyone can see the cumulative effect on the contract sum at any point in the job.

Variations are often confused with other adjustments to a contract price, but each has a distinct meaning:

• Variation vs provisional sum adjustment — a provisional sum is reconciled to the actual cost of work that was always part of the contract but undefined; a variation changes the scope itself.
• Variation vs claim — a claim (or “extension of time claim”) seeks compensation or extra time for an event, such as a delay, without necessarily changing the physical scope of work.
• Variation vs defect rectification — fixing defective work to the original standard is not a variation, since no scope has changed; it is simply completing what was already contracted.

Most variation disputes trace back to a handful of avoidable mistakes:

• Starting the extra work before it is priced and approved, leaving the contractor with no agreed basis to be paid.
• Verbal instructions that are never confirmed in writing, so there is no record of what was actually agreed.
• Pricing a variation against the wrong contract rate, or failing to check whether an item is already covered by an existing rate.
• Letting variations pile up unpriced until the final account, when memories fade and disputes become far harder to resolve.