Construction-works that are not estimated or valued in the accepted offer of a public tendering process are not included in a lump-sum contract price, and constitute extra works. A lump-sum price construction contract does not include works that both the tenderer and the successful bidder (the contractor) consider to be extra. The contractor is not obliged by the contract to execute those extra works. The contractor’s denial to execute the works is not a breach of contract. The Defendant is sentenced to pay for the works effectively executed under the contract, and to restitute to the Plaintiff payment guarantees, even if a legislative mandate considers the tenderer is not a formal party to the contract. The author argues the tenderer is the owner of the land and the works, and that payments to the contractor comply with two purposes. The first is paying for the building, as the owner has to. The second is anticipating public housing subsidies to its final beneficiaries.Las obras o partidas adicionales, no valorizadas en la propuesta aceptada de un proceso de licitación público, no están incluidas en un contrato de precio a valor fijo. Un contrato a valor fijo no incluye partidas que licitante y proponente (la constructora) consideran obras extraordinarias. La constructora no está obligada por el contrato a ejecutar dichas obras. Su negativa a efectuarlas no es constitutiva de incumplimiento contractual. El demandado es condenado a pagar por los trabajos efectivamente ejecutados, y a restituir garantías indebidamente cobradas al demandante. El demandado tiene interés en el contrato como dueño de los terrenos y de la obra. Los pagos efectuados al contratista cumplen dos objetivos. El pagar por la construcción, como dueño de ella. El anticipar el subsidio habitacionales a sus beneficiarios finales.