Casa in Sasso

Structural and deep energy retrofit for historic stone home in a hamlet near Scandiano (RE), Italy.


This three-story house is part of an historic ‘borgo’ (hamlet) comprised of several stone buildings dating to at least the 18th Century, with foundations probably from before. The house had not undergone any renovations since the 1950’s or 60’s. Our clients were a young Italian family of three, and our design brief was to renovate the house to meet current national Italian seismic standards and a level of energy efficiency that would make the project eligible for governmental tax breaks.

As with many historic structures in Italy, there were a number of existing challenges.

Previous additions:
– There had been an addition to the historic structure in order to facilitate bathrooms, which formed a three story tower on the front of the house. Because this structure was falling apart, we demolished it and used the permitted volume to reconstruct a two-story space. This new section housed a utility space, a new bathroom and a roof terrace on top, allowing views over the hills of the Reggiani Apennines.

Weak historic structure:
The entire structural skeleton needing reinforcing, necessitating a dismantling of the roof and each slab individually, and then a reassembling of the structure. The roof structure had been precariously balancing atop an interior load-bearing wall with the thickness of only one brick. The third floor perimeter walls were also only one brick thick. In order to strengthen the interior load-bearing wall, we strengthened its foundation with an inverted reinforced concrete T-beam. We also added a second layer of UNI bricks, attached to the existing masonry structure with structural steel bars. The existing floor slabs, made of old wooden beams and traditional brick tiles, were reinforced with concrete slabs and connected to the anti-seismic “ring beam” (“cordolo” in Italian) that runs along the perimeter. The client also provided a reclaimed historic oak beam from another building’s demolition as a structural reinforcement in the bedroom.

Ground moisture, mold, condensation:
There was evidence of ground moisture seeping up into the masonry foundation, a problem which is fairly common in this part of Italy with stone and brick buildings. In order to resolve this problem, we excavated below the ground floor and designed a ventilated system under the slab, where a corrugated tube allows external air to circulate through two separate holes in the foundation walls. On top of this, we placed a layer of glass foam granulate (GFG) to act as thermal insulation between the ground and the slab. We used in situ waterproofing of the foundation with a liquid membrane coating instead of the traditional sheets; this ensures a higher level of cohesion and a tighter waterproof seal.

Thermal envelope:
Because the home is located in a traditional ‘borgo’, two sides of the house share the wall with the neighbors, removing the option of external insulation. In these cases, we used thermal insulating plaster on the interior to resolve thermal bridges that might otherwise cause future problems with mold and condensation. For the stone masonry that faced out, we were able to use an external insulation system (“cappotto” in Italian). In this way, we maintained the beautiful stone work as visible from the interior. Leaving the stone exposed to both the interior and the exterior would not have allowed the building to meet minimum energy performance requirements. Thermally insulating the external structure, leaving the mass of the stone wall in contact with the interior environment allows the house to remain more comfortable in the hot summers. The thermal bridge between the wall of the main structure and the roof terrace was avoided by separating them with glass foam granulate (GFG), so as not to cause any interruption of the insulation layer.

Replacing the roof:
The original ceramic tiles of the roof were set aside during the construction process for reuse in the final stages. The structure of the roof, however, was altered considerably. The existing wooden structure needed laminated wood beam reinforcements to meet seismic norm requirements. We added an airtight layer to the roof profile, with a vapor retardant membrane on the inside, that connects with the airtight layers of the perimeter walls (note: in the photo, they had not yet been connected). We added wood fiber insulation, in order to provide for thermal comfort in both winter and summer.

All existing wooden beams were sanded free of several layers of paint, to expose the natural wood. We added a border of thermal insulating plaster as an interior frame around each window to avoid any thermal bridges or leaks resulting from the installation of the windows. The clients were quite independent in choosing many of the interior finishes and furnishings, as well as the exterior color. The doors, for example, were sanded and reused from another historic home. Many of the traditional tiles were salvaged from the family’s extended relatives. The large solid, stone kitchen sink was from the existing house. The wood floors were made and installed by a local artisan, using local oak, and installed beautifully to integrate with the stone on the interior walls. They selected a Jotul cast iron stove for the living room, and a traditional Italian cooking stove in the kitchen.

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