Purpose The purpose of this paper is to present an innovative approach for the development of a methodology to systematically assess the economic performance and for the assessment of the economic sustainability of a building, through the calculation of an economic sustainability index, within the sustainability framework according to the rules defined in EN 16627. Design/methodology/approach The methodology follows the principle of modularity, where aspects and impacts that influence the economic performance of the building during the phases of its life cycle are assigned to levels. It presents a model based on the construction costs of the building. The methodology in centered in the before use phase and restricted to residential buildings. Findings Definition of a model for assessing the economic performance and calculation of an economic sustainability index. Research limitations/implications The methodology is focused only in the before use phase of the buildings, assuming they have the same functional equivalent. It can be expanded to include the other phases of the building life cycle. Practical implications The developed methodology will allow the selection of construction procedures, based on economic sustainability, contributing to more rational and support decisions. Social implications Contributing to a more sustainable society. Originality/value The European framework of EN 15643 and EN 16627 for the assessment of building sustainability is new and, as such, not implemented in most practical tools. Also, economic sustainability is not usually considered in detail in existing models. This paper presents a methodology following the framework and, simultaneously, possible to integrate in existing approaches.