In light of increasing sustainability requirements, one of the challenges related to the heritage building stock consists in finding a balance between preserving the existing architectural character and improving energy efficiency. The project presented in this article has been carried out through a collaborative design process, involving experts from different disciplines (e.g. construction, energy, low-carbon materials, etc.), through a simulation-driven approach integrating both architectural and energy-performance evaluation aspects from the early-design phases of the project. In order to go as far as possible in terms of sustainability, the Living Building Challenge (LBC) label has been taken as a guide, providing a design framework to create regenerative spaces where people connect to daylighting, air, food, nature and community. It aims to obtain self-sufficient buildings from a holistic point of view (e.g. positive-energy building approach, treatment of the used-water onsite, prioritizing low-impact materials to obtain healthy living spaces). The project consists of the complete renovation of a rural home located in the medieval urban fabric of a small village called Bresca in the north of Spain. The initial construction date is unknown, but the house underwent a first basic renovation in 2007. The building consists of a typical farmhouse, well oriented regarding solar exposure, with poorly insulated massive walls and no heating system. The renovation project includes both passive and active strategies, improving thermal insulation of the building envelope and integrating a sunspace that helps to reduce heating and lighting demand, in addition to a photovoltaics (PV) installation with storage system that feeds a high-performance heat pump. This paper focuses on the energy aspects, comparing design results and post-occupancy evaluation in terms of energy consumption/production (energy performance gap). We highlight the high energy performance achieved while surmounting the architectural challenges related to the heritage constraints of the existing building. Results show that between February and March 2019, the house produced 858 and consumed 508 kWh, demonstrating that it is possible to achieve high levels of annual PV coverage ratio while respecting and valuing traditional architecture.