How to Price Variations in JCT Contracts

Every quantity surveyor who has worked on a JCT project has spent time arguing over the price of a variation. Pricing variations JCT contract instructions correctly is not optional extra reading - it is one of the most frequently used, and most frequently disputed, parts of the contract. Under the JCT Standard Building Contract, once the architect or contract administrator issues a written instruction requiring a change, the Valuation Rules at clauses 5.6 to 5.10 set out exactly how that change should be priced. Get the hierarchy right and the valuation is defensible. Get it wrong and it becomes a final account argument that drags on for months.

The rules themselves are not complicated in structure - they run in a strict order, from using the rates already in the contract, through adjusted rates, to fair rates, and finally to daywork as a last resort. What trips surveyors up is applying judgement at each tier: deciding whether work is genuinely 'similar', whether a quantity change is 'significant', and what counts as a 'fair' rate when nothing in the bills comes close. Those judgement calls are where most disputes over variations JCT contract pricing actually originate.

This guide sets out the valuation hierarchy in the order JCT applies it, works through a realistic priced example so the mechanics are clear, lists the documentation a QS needs to support a valuation under scrutiny, and covers the disputes that recur most often when contract administrators and contractors cannot agree a figure.

By the end you should be able to look at any variation instruction, identify which tier of the valuation rules applies, and build a rate you can defend at valuation stage rather than at adjudication.

The JCT Valuation Rules Hierarchy Explained

The Valuation Rules exist to stop every variation becoming a fresh negotiation from a blank page. Instead, they force the quantity surveyor to work down a fixed sequence of tests, starting with the rates the parties already agreed at tender and only moving to the next tier when the previous one genuinely does not fit. Clause 5.6 of the JCT Standard Building Contract covers work that can be properly valued by measurement, and it is here that the hierarchy sits.

Two things are easy to miss when applying this table. First, the test at Tier 1 and Tier 2 is not simply 'is there a rate for this item' - it is whether the work is of similar character and executed under similar conditions. A rate for forming an opening in a stud partition is not automatically the right starting point for forming an opening in a load-bearing block wall, even if both are described loosely as 'openings' in the bills. Second, 'significant change in quantity' triggering Tier 2 is a matter of degree, not a fixed percentage - JCT deliberately leaves it as a judgement for the quantity surveyor, which is exactly why a documented rationale for the tier chosen matters so much at final account stage. Where a QS cannot point to a clear reason for skipping a tier, a contract administrator - or an adjudicator reviewing the file later - is entitled to assume the lower tier should have applied, which is a costly assumption to leave unchallenged.

How Each Valuation Method Works in Practice

Contract rates and pro-rata rates

Where a bill rate applies directly under Tier 1, the valuation is mechanical - multiply the measured quantity of varied work by the existing rate. Pro-rata valuation under Tier 2 is where more skill is needed: the surveyor starts from the existing rate but adjusts it to reflect the reason the work is no longer 'similar conditions'. Common adjustments include restricted access, out-of-sequence working, small quantities that lose the economy of scale priced into the original rate, or additional preliminaries-type cost such as extra plant standing time. The adjustment should be evidenced, not guessed - a note explaining why the rate has moved from £42/m2 to £58/m2, and by how much for each cost driver, is what survives scrutiny.

Fair rates and prices

When nothing in the Contract Bills is genuinely comparable, Tier 3 requires a fair rate and price built from first principles - typically labour hours at a realistic gang rate, materials at current cost, plant where used, and an allowance for overheads and profit consistent with the levels priced elsewhere in the contract. Fair does not mean generous to either party; case law and JCT guidance are consistent that a fair valuation should reflect the reasonable cost of carrying out the work if reasonably and properly incurred, not a market rate pulled from a different job.

Daywork

Daywork under clause 5.7 is valued using vouchers recording actual labour hours, materials and plant used, priced against the RICS/BEC/CECA Definition of Prime Cost with percentage additions the contractor priced at tender for overheads and profit. Because daywork is priced on time and materials rather than output, it is the tier most open to abuse if vouchers are not signed contemporaneously - which is exactly why most contract administrators only accept it as a genuine last resort, and only where the contractor can show the work truly could not be measured.

• Always record which tier was applied and why - a one-line rationale on the valuation saves hours of argument at final account stage.
• A Schedule 2 Quotation is a separate route under SBC: the employer invites a priced quotation for the instruction before it is carried out, giving cost certainty upfront instead of valuing after the event.
• Where a variation instruction also disrupts other work, remember that direct loss and expense is a separate claim under clause 4.23, not part of the Tier 1-4 valuation itself.

Worked Example: Pricing a Variation Step by Step

Consider a variation instructing the contractor to form an additional 900mm x 2100mm doorway opening through an existing load-bearing blockwork wall, including a new steel lintel and making good to both faces. The Contract Bills price openings formed in timber stud partitions at £145 each, but there is no comparable item for openings in load-bearing masonry.

Notice what makes this valuation robust: the QS did not simply pick the nearest bill rate and inflate it. They tested the work against Tier 1 and Tier 2, ruled both out because the character of the work genuinely differs, and only then built a fair rate from labour, material and plant records. That sequence - test, rule out, justify - is what a contract administrator or, if it comes to it, an adjudicator will want to see reconstructed from the file.

Documentation You Need to Support a Variation Valuation

A valuation is only as strong as the paper trail behind it. Under JCT, the starting point is always a written instruction - clause 3.14 confirms a variation must be instructed by the architect or contract administrator, and clause 3.13 sets out the process for a contractor to confirm an oral instruction in writing if one is given on site. Without a valid instruction, there is no variation to value in the first place, regardless of how reasonable the work carried out might have been.

• The written instruction itself, or the contractor's confirmation notice if the instruction was given orally on site.
• Marked-up drawings or a scope description showing exactly what changed against the original design.
• Measured quantities for the varied work, cross-referenced to the relevant Contract Bills item where one exists.
• The rationale for which valuation tier was applied, and why the preceding tiers were ruled out.
• For pro-rata and fair-rate valuations, a build-up showing labour hours, material costs, plant and the overhead/profit percentage used.
• For daywork, signed daywork vouchers recording hours, operatives, plant and materials on the day the work was carried out - not reconstructed afterwards.
• A note of any related loss and expense claim kept separate from the variation valuation itself, since the two run under different contract mechanisms.

Contractors who keep this file live, updating it as each variation is instructed rather than reconstructing it at final account stage, consistently negotiate faster and more favourable settlements. Contract administrators, in turn, are far more willing to agree a fair rate quickly when the build-up in front of them is transparent and traceable to source records rather than a single asserted figure.

Common Disputes Over Variation Pricing

Most disputes over variations JCT contract valuations trace back to a small number of recurring flashpoints rather than genuinely novel points of interpretation. Recognising them early, and addressing them in the valuation build-up before they are raised, prevents a straightforward pricing exercise turning into a final account stand-off.

• Disagreement over which tier applies. Contractors often push straight to fair rates because they are usually higher than an adjusted bill rate; contract administrators often resist moving off Tier 1 even where conditions have clearly changed. The fix is a documented, objective comparison of the work's character and conditions against the original bill item.
• 'Significant change in quantity' left undefined. JCT does not set a percentage threshold, so parties frequently disagree on whether a 30% or 50% quantity increase is 'significant'. Precedent decisions and industry guidance are useful here, but a consistent, stated project-level approach agreed early avoids repeated arguments.
• Daywork used as a default rather than a last resort. Where measurement was genuinely possible, contract administrators are entitled to reject a daywork valuation and require the work to be re-priced under clauses 5.6, which can significantly reduce the value if vouchers were generous.
• Loss and expense bundled into the variation rate. Extending programme disruption costs or preliminaries thickening into what should be a straightforward measured or fair-rate valuation muddies both claims and weakens each one's evidential basis.
• Overheads and profit applied inconsistently. Fair rate build-ups should apply a percentage consistent with what the contractor priced at tender, not a higher figure introduced only once work moves outside the original bills.
• Late instructions confirmed only verbally. Where a site instruction is never confirmed in writing under clause 3.13, the contract administrator can dispute that a valid variation exists at all, leaving the contractor to prove both the instruction and its value.

Frequently Asked Questions

What are the JCT valuation rules for variations?

The JCT Valuation Rules at clauses 5.6 to 5.10 of the Standard Building Contract set out a hierarchy for pricing variations: original bill rates where work is similar and conditions are unchanged, adjusted pro-rata rates where conditions or quantity change significantly, fair rates and prices where the work is not similar to anything priced, and daywork as a last resort where measurement is not possible.

Which clause covers variations in a JCT contract?

Clause 3.14 of the JCT Standard Building Contract defines what constitutes a variation and confirms it must be instructed by the architect or contract administrator. Clause 5.6 to 5.10 then sets out how that variation is valued once instructed.

How is daywork valued under JCT?

Daywork under clause 5.7 is priced using signed vouchers recording actual labour hours, materials and plant used, valued against the RICS/BEC/CECA Definition of Prime Cost, with percentage additions for overheads and profit that the contractor priced in the Contract Bills at tender stage.

Can a contractor claim loss and expense on top of a variation valuation?

Yes, but it runs as a separate claim. The variation valuation under clauses 5.6-5.10 covers the direct cost of the changed work itself. Any wider disruption or prolongation cost caused by the variation is claimed as direct loss and expense under clause 4.23, and the two should be evidenced and valued separately.

What is a Schedule 2 Quotation under JCT?

A Schedule 2 Quotation is an alternative valuation route under the JCT Standard Building Contract where the contractor prices a proposed variation instruction upfront, before carrying out the work, giving the employer cost and time certainty in advance rather than valuing the work retrospectively under the Valuation Rules.

Who is responsible for valuing variations on a JCT contract?

The quantity surveyor, acting under the contract administrator or architect, values variations under a JCT contract. The contractor is entitled to be present when measurements are taken and can submit its own priced build-up, but the contract administrator issues the final valuation for inclusion in interim certificates and the final account.

What happens if the contractor and employer cannot agree the value of a variation?

If a variation valuation cannot be agreed, either party can refer the dispute to adjudication under the JCT contract's dispute resolution provisions, which gives a binding decision within a set timescale. Keeping thorough contemporaneous records of instructions, quantities and rate build-ups is what determines the outcome in the vast majority of these referrals.

Final Thoughts

Pricing variations under a JCT contract rewards discipline more than negotiating skill. The valuation rules hierarchy at clauses 5.6 to 5.10 is designed to be worked through in order - contract rates, pro-rata rates, fair rates, daywork - and most disputes arise when a party jumps a tier without justifying why the previous one does not apply.

Build the habit of testing every variation against the hierarchy explicitly, documenting the tier chosen and why, and keeping labour, material and plant records live rather than reconstructed after the event. QSs who do this consistently spend far less time defending variation valuations at final account stage, and settle far more of them at first submission.

Want the full picture? Want the fuller JCT picture?

This guide sits alongside our wider JCT coverage - read JCT Standard Building Contract: What QSs Need to Know for the full contract context, and Variation Orders in Construction: A Complete QS Guide for how variations are instructed and managed end to end.