The rehabilitation of ruined buildings, particularly within sensitive heritage contexts, raises critical questions concerning authenticity, material integrity, and sustainability. This article analyses two distinct interventions in classified rural territories, both facing challenges related to structural collapse and heritage regulation. The Granary House project, in Vinhós, exemplifies a case of critical continuity following the partial collapse of the original granite structure. The design response was based on the full reuse of the stone and the preservation of the vernacular grammar, incorporating discreet technical improvements that respect the existing material expression. The intervention embraces the new through controlled contrast, acting as a mediation between permanence and transformation, in line with the theoretical approaches of Carbonara, Frampton, and Zumthor. The second case, in the Aldeia Histórica of Castelo Novo, involves the rehabilitation and extension of two dwellings located within a legally protected ensemble. The proposal reconciles the preservation of the original scale and form with contemporary housing needs, while addressing regulatory and construction-related constraints. The decision to make the intervention visible—either through material contrast or formal updating—avoids mimicry and reinforces an evolutionary reading of the building. Issues such as the loss of usable area due to thermal insulation, or the difficulty in meeting current regulatory minimums, highlight the need for critical approaches to existing standards, as discussed by Valentim. Both projects reveal that sustainability in rehabilitation is inseparable from heritage responsibility, demonstrating that it is possible to intervene with ethics, coherence, and critical awareness—balancing memory, function, and contemporaneity.