How to Value Variations Properly (And Stop Leaving Money on the Table)

Variations are the lifeblood of construction commercial management. On most fit-out and refurbishment projects, the final account will include 10-20% in variations — sometimes significantly more. The difference between a project that makes 8% margin and one that makes 2% often comes down to how well variations are managed.

And yet, I consistently see small contractors handle variations badly. Late notifications, poor records, undervalued claims, and — worst of all — work carried out without any instruction at all because "the site manager agreed it with the architect." That's not variation management. That's giving money away.

The Basics: What Is a Variation?

Under JCT contracts, a variation is broadly defined as a change to the design, quality, or quantity of the works, including additions, omissions, substitutions, alterations to the kind or standard of materials, or changes to the order or period of carrying out the work.

The key principle is simple: if you're asked to do something that isn't in your contract, or to do something differently from what's in your contract, that's a variation and you're entitled to be paid for it. The complication, as always, is in the detail.

Identify It

The first step is recognising when a variation has occurred. This sounds obvious, but on a busy site, changes creep in without anyone formally acknowledging them as variations:

The architect asks the site manager to move a door opening 300mm. That's a variation — it affects the partitioning, possibly the floor finish, possibly the services. But if nobody records it as an instruction, it just gets absorbed into the works.

The structural engineer's latest drawing shows additional steelwork that wasn't on the tender drawing. That's a variation — but if the steel subcontractor just prices it and builds it without the main contractor capturing it as a change, the main contractor loses the margin.

The client asks for an upgraded floor finish in the reception. Everyone agrees it looks better. Nobody issues a formal instruction. Three months later, the QS queries the cost, and now you're in an argument about whether it was instructed or whether you just decided to upgrade it yourself.

Every one of these scenarios happens on real projects, every week. The solution is straightforward: train your site team to recognise changes and report them immediately.

Notify

Most construction contracts require the contractor to give notice of a variation within a specified period. Under JCT, the position depends on whether the variation was instructed by the architect or arises from another cause, but the principle of timely notification applies throughout.

The notification should be in writing, should reference the instruction or event that triggered the change, should describe the work affected, and should state that you consider it to be a variation with cost and/or time implications. Early notification achieves several things: it puts the client on notice that there's a cost consequence, it gives the design team an opportunity to reconsider if the cost is too high, and it creates a paper trail that supports your valuation later.

Late notification — or no notification at all — is the single biggest reason contractors fail to recover variation costs. By the time you raise it at final account stage, the client's QS has the upper hand: "If it was really a variation, why didn't you tell us at the time?"

Record

Before you value a variation, you need records that support the valuation. These should include:

The instruction or event that triggered the change. A copy of the architect's instruction, the revised drawing, the site meeting minutes where the change was discussed — whatever documents evidence that the work was changed.

The impact on your work. What additional work was required? What work was omitted? What was the effect on programme? Did it cause disruption to other trades? Be specific.

The resources expended. If the variation involves additional labour, keep timesheets. If it involves additional materials, keep delivery notes and invoices. If it involves subcontractor costs, get quotes or invoiced costs.

Photographs. Before and after photos can be powerful evidence, particularly for work that gets covered up by following trades.

Value

The valuation of variations under JCT follows a hierarchy:

Use contract rates where applicable. If the varied work is of a similar character and executed under similar conditions to work priced in the contract, the contract rates apply. This is the simplest approach and is usually appropriate for straightforward additions or omissions.

Use contract rates as a basis for analogous work. If the varied work is similar but not identical to priced work, the contract rates form the basis for a fair rate. You'd adjust for differences in scope, conditions, or difficulty.

Use a fair valuation. If the varied work has no reasonable basis in the contract rates — for example, work of a completely different character — a fair valuation is determined. This typically means building up a rate from first principles: labour, materials, plant, overheads, and profit.

Daywork. Where the work can't reasonably be valued using any of the above methods, daywork rates may apply. These should be the daywork rates stated in the contract or, failing that, rates derived from industry-standard definitions.

The critical thing with any valuation method is to be thorough and transparent. Show your working. If you're using contract rates, reference the specific items. If you're building up a fair rate, show the labour constants, material costs, waste factors, and overhead recovery. A well-presented valuation with supporting calculations is much harder for the client's QS to reject than a round-number lump sum.

The Mistakes That Cost You

Undervaluing your own work. Many small contractors, keen to maintain the relationship, price variations too cheaply. They forget to include for management time, extended preliminaries, the impact on productivity of working in an area that's already been fitted out, or the knock-on effects on other trades. A variation isn't just the direct cost of the changed work — it's the full cost to you of implementing that change.

Forgetting the time implications. Every variation that adds work, changes the sequence, or requires late information has a potential time impact. If a variation adds two weeks to the programme, you should be claiming the associated extension of time and any prolongation costs. These are often worth more than the variation itself.

Accepting "no cost" instructions. I've seen architects issue variation instructions marked "no cost impact." That's the architect's view. It might not be yours. If an instruction changes your work and costs you money, you're entitled to be paid regardless of what's written on the instruction.

Batch processing at final account. Accumulating variations and dumping them all at final account stage is a recipe for disputes. Value each variation as it occurs, submit it for agreement, and record the agreed value. This keeps the commercial position clear throughout the project and avoids the end-of-job argument about 40 unresolved variations.

Getting Organised

Variation management is fundamentally about organisation. You need a system that captures every change, tracks the notification, records the supporting information, and manages the valuation through to agreement.

In Construction AI, the financial module's variations tracker handles this — linked to the contract, cross-referenced with architect's instructions, with automated notifications and valuation templates. But even a well-managed spreadsheet can work if the discipline is there.

The discipline is the hard part. On a busy project, it's easy to let a "small" variation slide because you're focused on getting the work done. But those small variations add up. I've seen final accounts where £200,000 in variations was lost because nobody tracked the small changes during the project.

Every pound you don't claim is a pound off your margin.