Casa PB, the power of the unique shape of its roof

The Casa PB project was initiated under the Italian Home Plan (Piano Casa) of 2009 and it consisted in building a detached house on an area previously occupied by two above-ground garages. A partial change of use had to be requested for the new build, which has a larger volume than the previously existing garages. The house has the same grid lines as the previously existing garages and is adjacent to the main residential building of which it is an expansion, although it is completely detached from it. The Home Plan, an extraordinary measure which permitted its construction, allowed a certain degree of expansion of existing buildings in derogation of the urban planning instruments in force. The project therefore qualifies as an expansion of the adjacent residential unit located at the ground floor of a semi-detached house; Casa PB shares its garden with the main unit although it has its own specially-built driveway. Distances from other buildings and from boundaries as well as precise restrictions in terms of achievable volume were the first project elements to respect. Located in the south-east outskirts of Rome, Casa PB was completed in the early months of 2021. Built in reinforced concrete, it rests on a podium and it’s distinguished by the unique shape of its roof: a single surface that follows the direction of the wall with a sharp turn, crossing the exposed brick façade. The inside is arranged as follows: on the ground floor there are a living room with a kitchenette and a toilet, a utility room for the house’s technological systems and the garage, accessible both from the inside and from the outside; on the first floor there are two bedrooms, one bathroom and a large balcony that runs along three sides of the house. Living areas occupy less than 60 square metres, while the utility room and two-car garage measure 38 square metres. The living room and kitchen, where most time is spent, overlook the back of the lot which hosts the most intimate part of the garden, quieter than the nearby street. The podium makes for an outdoor extension of the living room itself since it has the same height as the inside and is covered by the projecting balcony on the first floor, allowing residents to eat or relax outdoors for most of the year. The wall structure of Casa PB is around 52 cm thick and is made up of a first layer of plaster measuring around 2 cm on the inside of the house, one 30 cm layer of lightweight hollow bricks aligned with the structural framework of the pillars, one 6 cm rock wool insulation layer and, on the outside a 12 cm face wall made of extruded bricks. The wall structure is one of the elements placing the building in the A4 energy class, which is the most efficient: using polystyrene all around the framework of the pillars avoids thermal bridges near structures. The extruded bricks on the outside make the house blend in well with its surroundings: most of the housing in the street where Casa PB is located consists of buildings with exposed brick walls. The architectural language of this new building, however, aims to reinterpret the use of bricks in a more contemporary perspective and to bring quality architecture to a less prestigious suburban context. While exposed bricks were chosen for the enclosure, travertine was the material of choice for the podium the house rests on: yet another tribute to ancient Rome that takes on a new, modern perspective. The bench at the westernmost end of the podium is also made in travertine: besides being a decorative element, it represents a physical boundary which closes off the podium area in front of the living room and makes it more intimate. Sheet metal panels were chosen for the roof covering: these were “sewn” onto the building on site with sartorial-like skill by using a double seaming technique. The ventilated roof is double pitched and the south facing slope houses photovoltaic and solar thermal panels. The photovoltaic panels produce around 2 kW of electric power whilst the 3 solar thermal panels produce hot water and power the underfloor heating circuits. The drainage channels of the roof covering convey rainwater, through downspouts, to an underground polyethylene reservoir of a capacity of 4500 litres located in the garden. The rainwater collected is then used for irrigation in the garden. The floor slab of the ground floor rests on a disposable formworks system which creates a 130 cm separation from the springing line of the foundations. The design project has concerned the entire building, with a particular focus on the interior where specially designed solutions were offered to optimise space. The staircase, the glass divider between the living room and the kitchen, the wardrobes and the walk-in wardrobe were all individually designed. The handmade staircase, made with a 3x3 cm zinc-plated iron tube, is suspended above a piece of oak furniture which is both a bookshelf and the final part of the staircase itself.