No work of any size finishes exactly as it was tendered. Foundations go deeper than the trial pits suggested, a client changes a floor finish, a specified fitting goes out of the market. The contract anticipates all of this — but it anticipates it through three distinct doors, and half the trouble in works offices comes from pushing a change through the wrong one. This article sets out the three doors in plain words and shows how to keep the record so clean that the deviation statement defends itself.
Three terms, three different things
The vocabulary matters because each word carries its own approval route and its own pricing rule.
- Deviation — a change in quantity of an item that is already in the agreement. The item, its specification and its rate all stand; only the executed quantity differs from the agreement quantity. Excavation tendered at 450 m³ that ends up at 610 m³ is a plus deviation; a plinth protection item dropped entirely is a minus deviation of 100 per cent.
- Extra item — an item of work that does not appear in the agreement at all but becomes necessary to complete the work as intended. Anti-termite treatment ordered after award, or a retaining wall nobody foresaw, are extras. There is no agreement rate to fall back on, so a rate must be derived and sanctioned afresh.
- Substitute item — an item executed in place of an agreement item. The tendered terrazzo flooring is replaced with vitrified tiles; the agreement item is closed (or reduced) and the substitute takes over its function. A substitution is really two entries moving together: a minus on the original and a plus on the replacement.
The test is simple. Same item, different quantity — deviation. New item, no parent in the agreement — extra. New item that displaces an agreement item — substitute. Write the classification down at the moment the change is ordered, not at billing time, because the classification decides who must sanction it and at what rate it will be paid.
Why limits and sanctions exist
A tendered contract is a competitive price for a defined scope. Every change made after award is, by definition, work priced without competition. Deviation limits — commonly a percentage of the contract value overall, with tighter individual-item ceilings — exist to keep that non-competitive portion small. If the scope can drift far enough, the low bidder who won on the tendered items can recover his margin on negotiated changes, and the economy of the tender evaporates.
Hence the sanction ladder. Small variations within the deviation limit sit inside the powers of the engineer administering the contract. Beyond the limit, the case travels upward: a deviation statement with reasons, a rate analysis for anything new, and approval by the authority whose financial powers cover the revised cost. Extra and substitute items usually carry their own, separate extents of sanction, because a new rate is a bigger decision than a changed quantity. Where the total cost effect pushes the work beyond the sanctioned estimate, a revised estimate becomes due as well — technical sanction has to keep pace with reality, not trail it.
Two practical rules follow. First, obtain sanction before execution wherever humanly possible; a post-facto sanction is a confession that control was lost. Second, treat the limit as a design constraint, not a nuisance — repeated breaches on the same division's works are exactly the pattern an audit team looks for.
How extra and substitute items are priced
A deviation needs no new rate: the agreement rate applies to the changed quantity (some contract forms do provide re-rating for quantities far beyond the tendered figure, so read the clause). Extras and substitutes, by contrast, always raise the rate question, and the answer comes from a fixed hierarchy:
- Derived from the schedule. If the item exists in the schedule of rates on which the tender was framed, take the schedule rate and apply the same tender premium or rebate that governs the agreement. This keeps the new item on the same commercial footing as the tendered ones and is the least arguable basis.
- Derived from analogous agreement items. Where the new work is a close cousin of a tendered item — the same operation with a different thickness or class — build the rate from the agreement item, adjusting only the element that changed.
- Market-justified analysis. Only when neither source serves is a fresh analysis of rates prepared from market prices of material and labour, with the standard allowances for overheads and profit. Market rates carry no tender premium — the premium expressed the bidder's view of schedule rates, and grafting it onto today's market prices double-counts.
For a substitute item, the cost effect is the difference: quantity × (rate of substitute − rate of the displaced item, pro-rated where the quantities differ). Record both legs. A statement that shows only the incoming item hides the saving or excess that the substitution actually caused.
Anatomy of the deviation statement
The deviation statement is the single document that reconciles the agreement with the work as it now stands. Whatever the printed form in your organisation, the logic is always the same four movements per item:
| Column | What it carries | Where it comes from |
|---|---|---|
| Item & specification | Agreement item number and description; extras and substitutes listed in their own sections | Agreement schedule / sanction orders |
| Agreement quantity & rate | The tendered quantity and the contract rate | The agreement, unaltered |
| Executed / anticipated quantity | Quantity done to date plus the quantity still expected — the statement looks forward, not just back | Measurement records and the engineer's forecast |
| Variation (+ / −) | Anticipated minus agreement quantity, item by item | Arithmetic — no judgement here |
| Cost effect | Variation × rate; substitutes shown as paired minus/plus; net excess or saving totalled at the foot | Rates as sanctioned |
| Reasons / remarks | Why the quantity moved or the item changed — the column that actually gets read | Site orders, drawings, correspondence |
The foot of the statement compares the net cost effect against the deviation limit and states plainly whether the variation is within the competent authority's powers. A statement without that closing comparison is a table, not a decision document.
The reasons column deserves care. "Increased as per site" convinces nobody. "Rock encountered at 1.2 m against 2.1 m assumed from trial pit TP-3; excavation in ordinary soil reduced, excavation in rock introduced as extra item vide sanction dated…" survives any scrutiny, because it ties the number to an event and the event to a record.
Documentation habits that survive audit
Audit rarely questions that quantities changed; it questions whether the change was controlled. Five habits settle the matter:
- Order first, record the order. Every change traces to a written instruction — a site order book entry, an approved drawing revision, a client letter. Undated verbal instructions are where recoveries begin.
- Classify at once. Label the change deviation / extra / substitute the day it arises, and open its rate case the same week if a new rate is needed.
- Measure contemporaneously. The details of measurement supporting a deviated quantity should carry dates consistent with the progress reports. Measurements recorded in one sitting at bill time have a signature all their own, and auditors know it.
- Keep the rate analysis with the sanction. An extra-item rate without its analysis, or an analysis without the sanctioning authority's signature, is half a document. File them together, with the market quotations where market rates were used.
- Revise the statement, don't overwrite it. Each version of the deviation statement is dated and superseded, never erased. The sequence of statements is the story of the work's control.
Keeping the statement in step with the bills
The traditional failure mode is drift: the RA bills march ahead with up-to-date quantities while the deviation statement, prepared once for a sanction long past, quietly goes stale. By the final bill the two disagree, and someone spends a weekend reconciling them.
Estimation-and-billing software removes the drift by construction. When the agreement, the bills and the statement share one data spine, the executed quantity in the deviation statement is the up-to-date quantity from the latest bill — not a copy of it. Enter a measured quantity once and every dependent document moves together: the bill abstract, the variation column, the cost effect, the comparison against the deviation limit. Extra and substitute items are registered once with their sanctioned rates and references, then flow into both the bill and the statement with the substitution's minus-and-plus pairing handled automatically. The engineer's judgement still drives the anticipated quantities and the reasons column — but the arithmetic, the carry-forward and the agreement baseline are no longer things that can silently diverge. That is what the billing module of eTAB Works-Estimator™ is built to do: one entry, one truth, every statement current on the day it is printed.
Related reading: RA bills from first to final · Analysis of rates, demystified · Building a detailed estimate · All articles