- Building Type : School, college, university
- Construction Year : 1800
- Delivery year : 2017
- Address 1 - street : 21 rue des Franciscains 68100 MULHOUSE , France
- Climate zone : [Cfb] Marine Mild Winter, warm summer, no dry season.
- Net Floor Area : 1 925 m2
- Construction/refurbishment cost : 2 900 000 €
- Cost/m2 : 1506.49 €/m2
Primary energy need :
(Calculation method : RT existant )
This case study presents the renovation of the Cour de Lorraine primary schools in the city of Mulhouse from 2015 to 2017. The renovation was accompanied by the construction of a new building, consisting of a canteen, sanitary facilities, an after-school reception area and a sports hall.
The aim of this renovation was to consolidate the structure of the building, to improve the management of fire and seismic risks, to improve the quality of the indoor air, to reduce energy consumption and to enhance and conserve the heritage, all at a controlled cost.
Changes in use
The building has already undergone many changes in use over time. Indeed, it was first a cloth factory, before being converted into offices, housing and workshops when a spinning mill was built in the yard. The building was converted into a school in 1871, when Alsace-Moselle became German: schooling was compulsory in Germany, whereas it was not yet in France.
During the renovation in 2015, the project leaders took advantage of the work to rethink the interior of the building. The building was redesigned to increase the school's capacity from 13 to 18 classes. The school canteen was moved to the new building, the boiler room and staff accommodation were removed and the ground floor of the existing building was transformed into classrooms.
Constraints and issues related to the old building
The building was suffering from a major problem of humidity. There were two main reasons for this:
- Firstly, its foundations were not deep, even though there are canals nearby. The water was therefore rising into the walls through the floor.
- On the other hand, previous renovations had been carried out with unsuitable insulating materials, such as cement plaster, which prevented water from evaporating from the walls.
- In addition, there was insufficient ventilation, which contributed to water stagnation. The structure of the whole building was therefore weakened by the excess moisture, resulting in numerous cracks.
This situation was a source of major energy losses.
Treating the moisture
- A 1.40 m strip of sandstone paving stones was laid between the school and the asphalt of the courtyard, to allow the moisture in the soil to evaporate
- Replacement of cement renderings on the exterior with lime renderings
Strengthening the structure
- Consolidating the foundations by injecting mortar under pressure
- Installing metal reinforcements to raise and anchor the inscribed stairs
- Insulation of walls and high floors with mineral wool and installation of hygrovapor brakes
- Insulating the floor with polyurethane
- Replacement of all intermediate floors with joist floors, with acoustic and fire regulations
- Replacement of carpentry in poor condition and restoration of others
Initially the walls were to be insulated with bio-based materials, but this was not possible for cost reasons (the project dates from 2015/2017, the cost of these materials has since fallen). The risk of condensation induced by the use of mineral wool had to be ruled out using the Glaser method
Installing efficient energy systems
- Installation of two gas condensing boilers in the new building, which also supply the school with heating and DHW
- Installation of underfloor heating on the ground floor
- Installation of a BMS to regulate the heating in the classrooms and to monitor the building's consumption in detail
- Installation of two double flow air handling units in the attic
The work required the opinion of the Architecte des Bâtiments de France and the Conservatoire Régional des Monuments Historiques, as some parts of the building are listed in the Inventaire des Monuments Historiques (one of the facades, two staircases and the roof). The heritage aspect of the building notably constrained the choice of insulation: insulation from the inside was preferred so as not to harm the school's facades.
See more details about this projecthttp://www.rehabilitation-bati-ancien.fr/fr/retours-d-experiences/rehabilitation-raisonnee-et-raisonnable-dune-ecole-primaire-0
Owner approach of sustainability
The very type of the site testifies to the project owner's sustainable development approach. In fact, rehabilitating the existing one made it possible to avoid building an entirely new school. This saves energy, materials and floor space. Renovation also makes it possible to reduce carbon emissions and the energy consumption of the existing one, which is just as important as building high-performance new buildings.
The city of Mulhouse, by renovating this building, has chosen to enhance and preserve the city's heritage. This makes it possible to offer schoolchildren and more generally the inhabitants a pleasant living environment, which recalls the history of the territory.
The architecture of the building contains remarkable heritage elements. The facade of the school on the street side, dating from the 18th century, includes sculpted decorations in blond sandstone as well as a triangular pediment pierced with an oculus. It has been listed in the Inventory of Historical Monuments since 1981, just like the roof and two staircases also from the 18th century. The second floor of the school has a rococo lounge. The survey also revealed the presence of original construction techniques, such as solid wood and plaster partitions dating from the 17th century.
The walls, 50 to 60 cm thick, are made of yellow sandstone and limestone, paved and coated with lime. They offer good thermal inertia to the building. The base stones, chaining and framing of the bays are in pink sandstone from the Vosges.
If you had to do it again?
Use bio-based materials whose price has fallen since the time of the work.
- Condensing gas boiler
- Low temperature floor heating
- Condensing gas boiler
- No cooling system
- Double flow heat exchanger
- No renewable energy systems
Guaranteeing the performance of what already exists is just as important as building high-performance new. This is why it is essential to tackle the renovation of the existing building. In particular the old frame, built before 1948, which represents 1/3 of the existing one.
This case study shows that it is quite possible to achieve good energy performance in renovation, even in buildings plagued by humidity with a weakened structure, all at a controlled cost. It shows that we can combine old buildings with modern and innovative energy systems. Finally, it shows that this type of building, thanks to efficient renovation, can offer a certain air quality and good internal comfort to its occupants. It is therefore an example for the rehabilitation of old buildings, often subject to similar issues.