Measurement overruns: the 10 % that is not a modification

Article 242.4 of Law 9/2017 (Ley de Contratos del Sector Público, LCSP), which governs modifications to the design proposed by the works director, lists two adjustments that "shall not be considered modifications" (unofficial translation). The first is excess quantities (exceso de mediciones): more units carried out than those in the design's bill of quantities, "provided that overall they do not represent an increase in expenditure greater than 10 per cent of the initial contract price". The text adds: "That excess in quantities shall be included in the final certificate of the works".

The second is new rates: the inclusion of new prices, agreed between the parties (fijados contradictoriamente), provided they do not increase the overall contract price or affect units of work that together exceed "3 per cent of the original budget". The mechanics of new agreed rates and of the modification regime are covered in the article on the limits on modifications in public works.

The General Regulation of the Public Administration Contracts Act (RGLCAP) completes the rule. Its article 160 allows variations in the number of units without prior approval where they do not represent "an increase in expenditure greater than 10 per cent of the original contract price, Value Added Tax excluded", and provides for payment in the monthly certificates or in the final certificate. Since that article refers to the previous law, the reference rule today is article 242.4 of the LCSP.

The 10% is measured across the contract as a whole, not item by item. One item can grow much more if others fall: what counts is the overall increase in expenditure. For tracking, that means keeping quantities item by item and adding increases and decreases together, because an unrecorded decrease gives a false sense of headroom.

A measurement overrun is not a route for changing the design either. It concerns units already provided for that turn out to be more numerous, not new units or changes of solution. A design change goes through the modification routes, with their own limits.

The excess quantities are included in the final certificate of the works, and that certificate has its own timetable. Article 243 LCSP provides for its approval "Within three months from acceptance", a period that the tender specifications may extend to up to 5 months for works with an estimated value above 12,000,000 euros whose final account and measurement are particularly complex. Then comes the guarantee period, which "may not be less than one year save in special cases", the director's report in the 15 days before it ends and, if favourable, the final account and payment "within sixty days".

For the budget, this has two consequences. First, the funding needed for the excess has to be available when the final certificate is approved, sometimes in a different financial year from the award. Second, by the time the amount is known precisely, the works have been accepted and there is no item left to offset it against.

Monthly certificates close nothing. Article 240.1 treats them as payments on account subject to correction at the final measurement, "without in any way implying approval and acceptance of the works". How to read progress certificates and the procedure for certifications and acceptance in public works are explained in their respective guides.

The practical rule is simple: the probable measurement overrun is reserved from the tender stage. The texts checked contain no automatic statutory reserve for this item; what the law establishes is that an excess of up to 10% is not a modification. It is for the authority to decide how much to reserve, according to the quality of the design's quantities.

The forecast is updated with every certificate. Item by item, the contract quantity is compared with the quantity carried out and with the one expected at completion. When an item halfway through execution has already reached its contract quantity, it signals an overrun; when the net running total approaches 10%, it is time to review the remaining design, before the limit forces another route.

The figures are fictitious. A works contract with an initial price of 1,500,000 euros, excluding VAT. The ceiling on excess quantities is 10%, that is, 150,000 euros. Halfway through the works, tracking shows:

The forecast excess, 95,000 euros, represents 6.3% of the initial price (95,000 / 1,500,000), within the limit. If the authority had reserved 75,000 euros, the forecast already requires 20,000 euros more funding. If the trend continued beyond 150,000 euros, the excess would no longer meet the condition in article 242.4 and it would be necessary to assess whether the remaining works can be readjusted or whether the change must go through the modification routes.

In private works there is no statutory 10%: the effect of a wrong quantity depends on the type of price agreed. The differences between fixed price and unit rates are covered in the quantities guide; for the budget, the following is enough.

With unit rates, the actual quantity makes the price. The promotor (the client or developer) pays for what is carried out, so the measurement overrun is its cost and the reserve plays the same role as in public works, without the 10% limit.

With a fixed price, a quantity error in an agreed design falls, in principle, on the contractor. Article 1593 of the Civil Code only allows a price increase for a change to the plan that produces an increase in the works and is authorised by the owner; a badly measured quantity on the same plan is not a change to the plan. Unless otherwise agreed, that reading protects the client, but in practice the dispute turns on the evidence and on what the contract says; see extra works under a fixed-price contract.

A measurement overrun and a price rise are different deviations and are kept on different lines. The overrun changes the quantity; revision changes the unit price according to a formula and a date. Mixing them makes it impossible to tell which part of the deviation comes from the design and which from the market. The second case is covered in price revision and the date of the budget, and its closure in the final account of the works.