The Château de Biscay stands on an ancient motte castrale on the border between the Basque Country and Béarn. It underwent multiple extensions and reworkings in the 18th century. Despite the house being in an appallingly poor state when the new owners acquired it, it was possible to restore the original elements that remained — walnut woodwork, stone floors, the remarkable 18th‑century parquet, and even the front door. This restoration was thought through down to the smallest detail while integrating all elements of modern comfort.

Because the owners wished to make the property their main residence, insulation and heating were major constraints in the design. The ground‑floor parquets were lifted to create a ventilated rubble layer (hérisson ventilé), on which rests a lime‑based concrete slab. Underfloor heating was installed in the entrance hall. Exterior joinery was replaced like‑for‑like with single glazing, while the original hardware was retained. Interior shutters were added for greater comfort and ease of use.

The house, thickened over successive extensions, had lost clarity in its circulation. In the dining room and the salon, openings were therefore created to re‑establish a double enfilade between the two rooms. A French door in the study was converted to a fixed window to make fuller use of that room, the service entrance now being accessible only through the kitchen.

The dining‑room woodwork, heavily damaged by termites, was removed and restored in the workshop. Interior doors were either restored or recreated to match the originals, and meticulous attention was paid to the choice of locks and light switches.

On the upper floor, degraded and non‑functional floorboards were consolidated or restructured. Three bathrooms were created.