Another successful example of passive house retrofitting in social housing was carried out in Paris (7-19, Rue des Orteaux), where 20 flats where delivered at the end of 2012 after 2 years of refurbishment. The project started with consultation among the different actors involved, namely residents, associations, developers and technical services for the city. This interaction allowed understanding the needs of the tenants, coordinating and developing the process to ensure its success. The building which was refurbished was previously a school and the project involved also action on the green spaces in the yard at the centre of the block (Build up, 2014).
During the refurbishment, glass double skin coatings were applied to the walls facing the sun. Insulated solid walls were used on the shaded façades of the building. The "double skin" assemblage walls rely on the use of passive solar thermal energy. In fact the solar energy is absorbed and stored within the collector walls which then heat the surrounding air before its arrival for air renewal to the interior space of the rooms. The preheating process reduces most of the energy needs used for heating the rooms during winter. The design optimizes the natural light in the apartments; in fact, most of them have a south, south-east orientation and face the street or the garden (Build up, 2014).
Apart from capturing the solar energy, the refurbishment aimed at achieving high energy insulation. When possible, the insulation was placed on the outside, limiting thermal bridges (R ≥5 Km² / W) otherwise on the inside (R ≥ 5.3 Km² / W) coupled with thermal bridge breakers at the slab (Ψ ≤ 0.25 W/ml.K). On the roof, external insulation was also applied (R ≥5 Km² / W) while on the ground level, the parking floors have been re-insulated on the underside (R ≥ 6 Km² / W), with a vertical drop of insulation of at least 50 cm - the floors on the mezzanine were also insulated on the underside (R ≥ 5 Km²/W, cellular glass type "foamglass" or equivalent). Thanks to these insulation measures the performance of the refurbished envelop achieved 0.56W/m2K (Build up, 2014)
After refurbishment the primary energy requirement of the flat achieved 49.8 KWh/m2yr meeting the passive house standard. Greenhouse gas emissions were calculated as 10kgCO2/m2yr.
The cost of the refurbishment was 3,750,000€ which was partially funded (60%) by the municipality of Paris and by SIEMP (City of Paris Real Estate) which is a Public-Private Joint Venture (Build up, 2014)
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Figure 1: Outside view of the refurbished social houses in Paris (Build up, 2014)