The “tree house” occupies the top of a small early 20th-century building, set within a fabric of garden villas surrounded by taller residential blocks. The intervention completely redefines the upper portion of the building, introducing two new levels designed from scratch. The internal layout is based on a careful measurement of space in plan and section, adapting it to the needs of a family of four. On the third floor, the partitions of the sleeping area and service spaces align with the timber beams of the floor and the frames of the perimeter windows, integrating the structure into the architecture. The distribution is reduced to the essential, prioritising usable living space. Each room is accessed directly from the living area through recessed doorways that preserve privacy; alternatively, rooms are connected through openings that allow movement from one space to another, creating visual continuity and a sense of shared living. The living area, open towards the city, extends up to the attic level, from which a small elevated garden can be accessed - a green contribution within the high-density urban context. To optimise space, all fixed furnishings are custom-designed. Despite the limited ceiling heights, heating and cooling systems and lighting fixtures are fully concealed. Materials interact through a balance of smooth, rough and reflective surfaces. The perimeter greenery acts as a threshold, filtering the surrounding urban fabric and giving the more private spaces a sheltered and intimate character.