The house is built of concrete, larch-wood, triple-glazed pine windows, flat concrete and pitched tiled roofs. The material that stands out the most however is of course stone: the existing ruined walls of small stone and the new walls of solid blocks. The stone, called “pierre du gard” or “pierre du vers”, is quarried in Vers, next to the Pont du Gard. The stone is in fact extracted exactly where the Romans took stone to build the famous aqueduct, like the one represented on the 5 Euro note.
The stone is an ochre yellow limestone with shells, or fossils, and dates from the tertiary Neogene period, and the Helvetian bed, about 15 million years ago. The limestone has a large grain and high porosity, resembling crunchy breakfast cereal up close, with a granulated composition with air pockets. This makes the stone relatively breakable when thin, easy to cut and light, with a density around 1,95 (1950 kg/m3).
The stone has historically been used in large blocks, as a rather “cheap” mass, and is to be found as dividers in parking lots and in agricultural and industrial environments in the south. The stone was used in the post-war reconstruction in the south of France for public buildings and housing. The architect Fernand Pouillon used the stone in solid form to rebuild the waterfront of the old port of Marseille. After many years of decline, more recent architects have revived the material, particularly for large agricultural buildings like warehouses. Gilles Perraudin, a previous International Stone Architecture Award winner, has notably built some impressive wineries, and a recent, highly sculpted house.
For the stone house, the building code required using “stone-coloured” materials, and so it became evident that using real stone would be a much more pertinent solution. The Vers limestone is easy to extract and under-appreciated locally, so using large blocks also turned out to be financially viable.
The main issue for the house proved to be the poor soil for the foundations. The house is on a hill made largely of clay, which has a tendency to expand and contract depending on humidity and rain. This ground movement is particularly harmful to building foundations, perhaps explaining the fact that the existing stone walls were largely in ruins. The new house therefore sits on three-meter deep “massifs”, or thick pilings, and ground beams that anchor it to the slope. A floated concrete plate for the flooring avoids any potential buckling from soil movement.
The walls are made of 50 by 50 by 200 centimetre blocks stacked lengthwise. Attention was made to cutting the blocks in the same orientation as they were quarried, to avoid flaking from frost damage. The placing of the stones creates gaps for openings in the walls, doors and windows. Where there are flat concrete roofs, the last course of stone is only 30 centimetres thick to allow a 20-centimetre bed for the roof plate. Other walls have a 20 by 20 centimetre head-beam poured into the top stones to tie them together. As this is a seismic area, the engineers integrated concrete anchor columns into the walls. Although considered unnecessary by the masons, these columns were simply poured into hollowed forms in the stone filled with steel reinforcements, thereby tying the walls to the foundations.
The guest wing was designed using the existing walls, with only one added new wall and glazing enclosing the volume. The new wall was made using 1 meter by 1 meter by 50 centimetre thick blocks, staggered to create a fish-scale pattern. The office has since developed this experiment further for another project, a winery, soon to go into construction.
Traditional houses in the area are made of thick, rather porous stone walls, whose mass helps keep the houses cool during the hot summers. This idea, confirmed empirically, suggested that the house could be built without insulation. The client preferred this solution, signing off on the idea, and so the walls are left bare inside the building. The house’s thermal mass has proved a stabilizing force during the cold winters and hot summers, in part also due to attention paid to the orientation of the house and the shading overhangs protecting the large glazed bays from summer sun. Recent statistics have suggested that the stone has poor insulating properties, which remain to be seen on the ground. Nevertheless, as a precautionary measure a 10 centimetre gap was designed into the project along the inside of the few exposed stone walls, should the client find necessary to add interior insulation.
The existing stone walls have proved to be rather fragile, filled with clay in their center, and mostly built without foundations. What walls could be saved were partially regrouted and sealed from above in order to avoid water damage. The pool within the walls of one of the old buildings was also therefore built as a separate, inserted concrete volume, stabilising the existing ruins.
