The Círculo Ecuestre comprises two buildings: the Palacete Pérez Samanillo, the work of the architect Joan Josep Herás Arimendi, built in 1911 on the corner of Diagonal, and La Espuela, the spur, a ground-floor construction designed by the architect Raimon Duran i Reynals in the 1950s, overlooking Carrer Balmes.
The project for an extension with private rooms is located in Carrer Balmes and presents a unitary front of 28.75 metres that prevents the need to create a courtyard between the buildings. The façade designed by Duran i Reynals is extended, forming a long, coherent base above which the new five-storey building rises. The extension will accommodate members from outside Barcelona and meetings with members of similar bodies in other countries.
To assimilate the Carrer Balmes façade with the typical Eixample frontages surrounding it, it was given a solid-looking facing, clad with stone, arranged in keeping with the street layout and with a vertical strip of windows on the side facing the neighbouring plot.
The side façade in which the rooms are located, perpendicular to Carrer Balmes, is glazed, making it disappear as such, reflecting the side façade of the Palacete Peréz Samanillo. The façade that encloses the courtyard at the centre of the street block is similar to the glazed façade housing the rooms; part of it does not contain glass, the other is almost opaque.
This arrangement of the building and its façades means that the rooms are protected from the noise of busy Carrer Balmes. The building is accessed via the main entrance to the Círculo Ecuestre, in the Palacete Pérez Samanillo.
The extension also increased the surface area of the La Espuela restaurant and fitted out the roof terrace of the building designed by Duran i Reynals for use as a dining area.