The project starts with the need to connect two adjacent houses. These are two urban properties located in one of the expansion areas of the city of Terrassa, dating from the late 19th century and the first half of the 20th century. The plots have a practically rectangular geometry, except for the inclined back lintel of the plot, and they are southeast-facing along the long side.

The resulting house explores the potential of unifying both houses through the shared party wall. Moreover, the exterior garden space (inner courtyard) is expanded and conditioned. By connecting the different spaces of the house through new passages in this shared party wall, the housing scheme changes from a linear layout to an indeterminate matrix of spaces that allows for multiple living arrangements.

The house consists of a ground floor, a first floor, and an attic floor. Partition walls made of compacted earthblocks are proposed. Special attention has been given to the thermal envelope solution in order to minimize energy demand, both in the thermal insulation of the roofs and in the facades with higher heat loss. A shading system has been provided to regulate solar gain and prevent overheating and discomfort.

Efforts have been made to minimize the environmental impact of the proposal, both in terms of construction solutions and execution processes during the construction. Bioclimatic strategies are proposed, such as solar gain on the south facade, chimney effect ventilation through the central core, use of thermal inertia, humidity control, and natural lighting, to reduce energy consumption and improve comfort and health.

The central core intersects with the roof through two motorized windows that provide natural lighting, solar gain, and cross ventilation for all spaces in the house. The new core houses the different bathroom facilities, differentiated according to their use.

The typology of the house imposes purely structural constraints, offering an aggregated distribution that denies access and service cores with environmental qualities such as ventilation and lighting. By adding two adjacent houses, expanding this central area allows us to reverse these limitations and turn these central elements into drivers of environmental qualities. Thus, we turn the main scarcity of the pre-existing condition into a crucial element of the proposal.

The facade cladding, as well as the roof insulation, ensures thermal continuity that reduces renewable energy consumption by 60% compared to the CTE limit. BTC provides thermal inertia (similar to ceramic brick walls), but unlike ceramics, the earth also provides hygroscopic control. This ability to control indoor humidity represents an "extra" (and unique) comfort feature.