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    Site The centre of Osilo was built on a south facing hill slope, crowned by a medieval castle standing on a high cliff. The houses are located i… Read More
    Site The centre of Osilo was built on a south facing hill slope, crowned by a medieval castle standing on a high cliff. The houses are located in long rows that roughly follow the contour lines. The newer parts of the settlement follow the same principle, providing a rather uniform urban form. After thorough investigation, the old city centre confirmed to be a compact energy-conserving apparatus. Software simulations of a typical dwelling unit show that compactness could actually bear positive effects: a row house, compared with a freestanding house with the same shape and built with the same materials, displays a dampening of about 4 °C in the inner temperatures. Abandoned buildings, vacant lots, and one-story houses could then be considered as leaks in a compact fabric. Incidentally, they amount to the 20% of the total vertical surface. With its persisting medieval urban structure, the site seems the right place to experiment the advantages of compactness. Intentions The commission to redesign a small building into the cell of a spread-out hotel played an important role in developing and checking these concepts. It was soon apparent, that the building envelope is more than a way to control energy flows. Specifically, it assumes many other functions: it filters interferences and brings privacy, characterises buildings, divides the public from the private realm, and by means of variation and repetition, it builds up the whole appearance of a town. Put in other words, it is a primal architectural element. Moreover, the transformation of the envelope of each single house, if considered only in terms of energy efficiency, could produce unexpected shifts in the urban landscape, specifically in a dense old town. Then, every intervention must be consciously designed as a part of a whole. The need of an energy conscious design may help to escape formalism and cliches; at the same time facades, windows, and roofs are crucial components of the urban landscape. Spatial configuration The small one-story cell stands right under the castle. Its two short facades look on to the street and the garden respectively, while the surrounding buildings close its two long sides. Its mean length is 7.30 metres, its mean width of 2.70 metres, and its height from 3 to 5 metres. The massive walls are built with basalt stone, with an high thermal inertia, being 50 cm thick. The roof, covered with tiles and made with wooden beams and bricks, and the floor, made by pressed earth, need a complete overhaul. The roof is also the most relevant element in exchanging heat with the surrounding and for landscape integration. A burnt beam and a pair of holes in the long walls witness the existence of an old gallery. There is no other opening except for the entrance door. Therefore, this small house seems a relevant specimen of this compact urban structure, both in its spatial arrangement and its construction. As a consequence of the strong constraints in the horizontal plane, the longitudinal section becomes the most effective architectural tool to change the relationship between the inner space and the outer climate, and with rather little effort. The roof shifts about 70 cm upwards allowing the insertion of two clerestories in the resulting gaps on the main and rear facade. These two openings extend daylight time over 200 lux and favour cross ventilation: the inner hot air is washed off during summer nights and replaced with cooler outside air. The higher ceiling leaves room for an intermediate wooden gallery that extends the living space and connects it to the backyard. The gallery parts the inner space in two zones with different thermal character: a cooler lower zone and a warmer upper zone, that could be used differently in summer and in winter, like in the ancient arabic houses. A new insulating shell covers the inner face of the existing walls, enabling the occupants to quickly warm or cool the inner space, an appreciated feature in an hotel room. The inner shell slightly folds to approximate the irregular shape of the existing walls, letting all plumbings run in the resulting interstitial spaces without carving slits in the stone. The roof is the most critical point, being the most extended exposed surface of the envelope. After evaluating some alternatives, giving more or less thermal inertia, a wooden roof, with a ventilated overlay and an insulating layer seems the most suitable construction. In fact simulations demonstrate that adding an inner layer of heavy material lowers the inner temperatures in the gallery only about 0.5 °C. This minuscule contribution gives no reason to bear the higher prices, the bulkier beams, and the general thicker appearance of an heavier roof. Considering its use and the derived internal gains and occupation patterns, the house needs winter heating, water heating, and electricity to power up small devices. A wood-burning stove seemed more appropriate: it can quickly heat the little interior volume, using a renewable resource easy to find on site. Furthermore, a thermal solar system with forced circulation supplies warm water. The system is made of a solar panel of 2 sqm and a 200 litres boiler. The boiler is equipped with an electrical resistance that can heat up the water in the winter period, if solar radiation is scarce. A 2 sqm on-grid photovoltaic module provides the required electrical power. The module produces in a year the amount of electricity needed in the six months when it is actually used; the system will send the energy to the grid and pull it back when needed, thus avoiding an oversizing of the panels to meet the summer energy peak. The solar-thermal collectors and photovoltaic cells stand in the higher part of the garden, well exposed to the sun and hidden from the castle’s view. Read Less
    Published:
Extension of the spread-out hotel, Osilo (Sardinia, Italy), 2007-08.
This small “spread-out” hotel cell  is actually a pilot project built within a research program on sustainable architecture within the EU “Campaign for Take-Off of Renewable Energy”.  
The medieval urban structure of the old city centre of Osilo is an ideal site to run a design experiment about the energy efficiency of a compact settlement. The experiment unfolds within an interdisciplinary framework, where design disciplines contribute through studies in architectural typology and urban morphology as well with tentative design, building technology analyses the construction methods and building materials, while social sciences use surveys to investigate the population needs.  

Energy efficient design is a challenge to complexity, hard to face without an interdisciplinary approach. The research program, and consequently this pilot project, focuses on recombining exiting technologies to introduce differential changes that could lead to a more efficient built environment. Old buildings and town centres are among the elements that could build an alternative sustainable settlement. Their sustainable refurbishment reduces building on virgin land and fully exploits the fundamental energy efficiency of dense settlements. Moreover, it gives a new use to all the grey energy embedded in the ancient walls.
This project is not simply the effort to prove that these assumptions are true. With it we started to investigate the idea that cultural heritage can become as an environmental heritage too.

General plan. 
Red: Spread-out hotel buildings. Black: prominent prublic buildings. 
1. Malaspina Castle. 2. Monte Granatico (Grain Storage). Spread-out hotel central building (refurbished). 3. House in Via Adelasia (refurbished). 4. House in via Malaspina (refurbished).5 6. House in via Malaspina. 6. House in via Eleonora d'Arborea.
Upper floor, showing the spatial articulation that achieves continuity between the street and the garden level.
Lower floor, showing the entrance from the street.
Daylight simulation with Radiance.
Inner temperature simulation: frequency of temperatures (%) in summer (left) and winter (right). The dotted line shows when backup climate system should kick in.
Inner temperature simulation: frequency of temperatures (days) in summer (left) and winter (right). 
View from the gallery, showing the clerestory window that provides cross air circulation and additional solar gains in winter, with the movable wooden shades.
Interior views, showing the clerestory window and the connection between the gallery and the steep rear garden.
Project team: 
Francesco Spanedda (Architectural design, on behalf of Dipartimento di Archiettura e Pianificazione dell'Università di Sassari), Giovannico Pinna (Engineering). Collaborators: Antonio Serra (Environmental design and sustainability), Antonio Pazzola (Material survey).