The two regimes
| Regime | Mechanics | Typical use |
|---|---|---|
| To be justified (a justificar) | The amount is a provision; what is actually executed is paid, justified with quantities and prices (contract prices or new rates) | Foreseeable but unquantifiable work at design stage: reinstatement after opening-up works, contingencies connecting to existing networks |
| Integral payment (de abono íntegro) | The amount is paid in full for the result, without subsequent measurement | Obligations of result that are definable but hard to measure by units: certifications, administrative processes, some global services |
The distinction is contractual and must appear in the item itself: a lump sum without a declared regime is a deferred dispute, because the contractor will read it as integral payment and the site direction as one to be justified. How the item is worded matters more here than any later verbal agreement.
Legitimate and illegitimate uses
Legitimate: what genuinely cannot be measured at design stage (interfaces with the existing building in renovation, reinstatement dependent on findings) and obligations of result with no natural unit. Illegitimate: definition laziness. A lump sum for "the unit's electrical installation" is not a work item, it is the absence of an electrical design; its amount will be disputed, its scope too, and the developer's negotiating position will be the worst possible, with the works underway.
The quantitative alarm signal: when lump sums exceed a small percentage of the PEM (prudent practice keeps them under 2-3 % in well-defined new construction), the budget is declaring design indefinition, and the offers received on it are incomparable precisely in that fraction. The remedy is not to shrink the lump sum but to define the design that makes it unnecessary.
The drafting rules
Four elements make a lump sum manageable. A declared regime (to be justified or integral payment). A described scope with the same discipline as any item: what it includes, what it excludes, what result is expected. A justification rule for lump sums to be justified: with which prices execution will be valued (contract prices where they exist, new rates otherwise). Treatment of surplus and excess: what happens if the justified amount falls below or above the provision.
In tender comparison, lump sums are isolated from the comparison table: they are uncompeted amounts that distort totals, and their correct analysis is to check that all offers treat them with the same regime and scope. Only afterwards are they reintegrated, on the same basis for every offer.
The essentials
The lump-sum item is an exceptional tool with two regimes that resemble each other in nothing: a provision to be justified or an integral-payment obligation. Its healthy use is recognisable by three traits: few of them, with declared regime and scope, and reserved for what genuinely cannot be measured. Every lump sum that substitutes for design definition will reappear as a new rate, at the worst moment and without competition.
Note: usual conventions in Spain in 2026; in public works, the lump-sum regime follows the applicable procurement rules.