Elementary School in Mulhouse, France

21 Bis rue des Franciscains

68100

Mulhouse, France

Architect

Pierre Lynde, Formats Urbains Architectes Associés
39 rue de Victor Schoelcher 68200 Mulhouse
contact@formats-urbains.fr
33 (0)3 89 33 27 90

Owner

Ville de Mulhouse - Pôle Education et Enfance
11 avenue du Président Kennedy 68200 Mulhouse
education-enfance@mulhouse-alsace.fr
(+33)3 89 32 58 72

Contact Details

Elodie HEBERLE
Cerema
elodie.heberle@cerema.fr
+33388777931

Other Information

Visits
Please contact Ville de Mulhouse to visit the school outside of class hours.

Related publications
The school is one of the case studies of the CREBA (French knowledge center for responsible retrofit of heritage building) website.
General picture of the building (author : CREBA)
This hard-stone elementary school is located in Mulhouse in the Alsace region (north-eastern France), near the border with Germany. It is a listed building, as it witnesses the history of the city of Mulhouse : it first was a spinning factory at a time which Mulhouse was well-known for its textile industry and became a school after the annexation of Alsace and Moselle by Germany in 1870. It has recently been retrofitted. The project reaches a balance between low energy consumption and heritage preservation, despite a constraint budget. The school is one of the case studies of the CREBA (French knowledge center for responsible retrofit of heritage building) website.
Energy performance
69 kWh/m2.y

Climate Zone Cfb

Altitude 301

HDD 1961

CDD 719

Protection level Listed

Conservation Area:
No

Level of Protection:
The street-facing façade, the roof and two inner staircases are classified on the French supplementary historic monument list.

Building age 1700-1800

Year of last renovation:
2015

Year of previous renovation:
1980

Building use Educational/Research

Secondary use:
NA

Building occupancy:
Discontinuous occupancy (i.e. holiday home)

Number of occupants/users:
300

Building area Net floor area [m²]: 1925,0

Building typology:
Detached house

Number of floors:
2

Basement yes/no:
Oui

Number of heated floors:
2

Gross floor area [m²]:
1925,0

Thermal envelope area [m²]:
5775,0

Volume [m³]:
5775,0

NFA calculation method:
SHON (fr)

Construction type
Stone masonry wall

External finish:
Rendered

Internal finish:
Lime coating

Roof type:
Pitched roof

+ MORE - LESS
General picture of the building (author : CREBA)
General picture of the building (author : CREBA)
3d-view of the building (author : Pierre Lynde)
3d-view of the building (author : Pierre Lynde)
City map from 1642 (author : Wikipédia)
City map from 1642 (author : Wikipédia)
Sandstone and limestone (author : Pierre Lynde))
Sandstone and limestone (author : Pierre Lynde))
Mass lay-out (author : CREBA)
Mass lay-out (author : CREBA)
Main facade (author : CREBA)
Main facade (author : CREBA)
Mercury's head (author : CREBA)
Mercury's head (author : CREBA)
Listed staircase during the works (author : Pierre Lynde)
Listed staircase during the works (author : Pierre Lynde)
Rococo style lounge (author : CREBA)
Rococo style lounge (author : CREBA)
Cement coating and cracks (author : Pierre Lynde)
Cement coating and cracks (author : Pierre Lynde)
Wall tilting inwards (author : Pierre Lynde)
Wall tilting inwards (author : Pierre Lynde)

RENOVATION PROCESS

Architecture

BUILDING DESCRIPTION

The school is located in Mulhouse, the third city of the Alsace region after Strasbourg and Colmar. The parcel is known since 1726 as the "Cour de Lorraine" (backyard of Lorraine), due to the origin of its first owner, coming from the neighbouring Lorraine region. The building was probably bought in the mid-18th century by the famous Mulhousian industrialist Jean-Henri Dollfus, to install a cotton priting factory (called "indiennes"). In the beginning of 1800, an imposing spinning factory was built in the backyard, in front of the building today sheltering the school (see mass lay-out : to the left, the parcel in 1825, to the right, the parcel today). This building was then dedicated to housing for the manager and his family and workshops. In 1870, the factory and the northern part of the building burned down. This part is still today ended by a blind gable wall. In 1871, Alsace-Moselle becomes German. Unlike in France, education is compulsory in Germany and raises a huge needs for schools. The "Cour de Lorraine" building is requisitioned and shelters since then an elementary school. Before retrofitting, the school welcomed over 300 pupils, split into 13 classes. The ground floor was occupied by the canteen, an official housing and a technical room. The building is built in Mulhouse intra-muros, which was long surrounded by canals (see the 1642 city plan). It has no real basement, the attic is inoccupied and the building as a shape of a "L" : the exterior façades are giving to the streets and the interior façades to the backyard. They are 60 cm thick and are made of rubbles of yellow sandstone and limestone. The lower sections, the horizontal string courses and the window frames are in pink Vosges sandstone. The building has a heated area of 1925 m² on three storeys. A gymnasium, that was built in 1891 in the backyard had been demolished in 2010.
Urban context
The building is located in the city-center of Mulhouse. At the time of its construction, it was in Mulhouse intra-muros, which was long surrounded by canals.

HERITAGE SIGNIFICANCE

ELEMENTS WORTHY OF PRESERVATION
The street-facing façade is remarkable : it is symetric with yellow sandstone decorations. One of these represents the head of the god of commerce Mercury and a lion's head. A triangular pediment, pierced by an oculus, and a carriage entrance were preserved. The entire façade is listed since 1981. A rococo style lounge, located in the second floor, is a rare remaining of the interior design, with the staircases and the ironwork. Some cast irons columns from the 19th century, which were meant to strengthen the structure, were reused as decorations. A complete survey of all the elements worthy of preservation was made by the regional commissioner for historic monumentsnd archived. The Survey revealed some original construction techniques, as solid wood and plaster partition walls from the 17th century, when the initial building was built on the parcel. Archeological excavations were conducted before the works. In the backyard, Gallo-Roman coins, a medieval enclosure and civilans protection galleries from World War I were found. In the inside of the building, a medieval basement was also discovered, surveyed and filled in with soil.
Heritage Value Assesment
The street-facing façade, the roof and two inner staircases (see picture) are classified on the French supplementary historic monument list : http://bit.ly/30YVwNO As a listed building, the validation of the works and the main façades, the roof and the two inner staircases by the Regional commissioner for historic monuments was required by regulation.
Heritage Assessment Files
Engraving of the spinning factory (author : Engelmann, 1823)
Engraving of the spinning factory (author : Engelmann, 1823)

State of repair

Conditions of the envelope
The presence of the canals, not deep enough foundations and the progressive replacement of the exterior lime coating with cement coating in the eighties (see picture) led to disorders : - insufficient stability of the structure : the foundations subsided from several centimeters, and so did the partition walls and the floors. The internal angle of the building showed cracks and tilted clearly inward (see picture). - moisture accumulation : Almost all the joists were mouldered and had already been repared in the past, possibly during the German annexation. Efflorescence were visible on the lower sections. Dry rot, developing in moist and dark areas, was also discovered at the foot of one of the listed staircases and immediatly treated, as it spreads very quickly and feeds on wood. The backyard of the school was depolluted after mercury was discovered while digging. Asbestos, coming from works carried out in the eighties, was also removed. Ventilation, which was provided by opening the windows, was also insufficient. The framework, which was replaced in the 19th century, was in good state. Double-glazing windows were installed progressively, from the nineties to more recently.
Description of pre-intervention building services
The school was never insulated before. A fuel boiler was installed in a technical room in the ground floor. The heat is distributed throughout the building by water circulating through pipes. Domestic hot water was provided by instant electric heaters, installed in sanitations.

Aim of retrofit

Renovation + Extension
The retrofitting project lasted from 2015 to 2017. This project is part of a wider program, aiming to retrofit all the Mulhousian schools and create the best conditions possible for pupils. The project in particular consists in two differents ones : - the retrofitting of the existing building - the construction of a new building in the backyard, sheltering the canteen, sanitations, rooms for after-school activities and a sports hall. Because of the presence of a listed building near the new construction, the validation of the works by the Alsatian architectural review board was required by regulation. For the retrofitting, the project owner had several objectives : - strengthening of the structure ; - adressing regulatory obligations, like the risk of fire and the seismic risk, as Mulhouse obtains the rating of 3 on the French seismic risk scale, going from 0 to 5, but also ensuring accessibility for disabled people ; - improving the indoor air quality, even above the French regulatory standards, but also the acoustic comfort ; - conserving the listed parts of the building but also the rare remaining of the interior design ; - keeping the costs under control, because of a restraint budget ; - and, of course, reducing the energy consumption. In the first version of the project, achieving the French low energy building ("Bâtiment basse consommation") label was not an objective. But thermal simulations showed that it was technically possible. Thanks to a grant from the Alsace Region and the French environment and energy management agency, the label was also financially achievable. The project management team was composed of an architect as the project supervisor and several engineering consultants specialised in building physics, structure, electricity, acoustics and building services. The craftspeople were coming from the near region and were medium-sized companies.
Lessons learned
The project management team used building information modeling (BIM) for the construction of the new building but also for the retrofitting of the existing one. This has prevented conflits between technical and architectural decisions. It was also a powerful tool to communicate with every stakeholders, including the project owner. This project was difficult in many ways : - first, it was a double project, with both a new construction and a retroffiting ; - then, mercury pollution in the backyard had not been anticipated, resulting in extra costs. - the retrofitting building was in a very bad state, because of structural issues, but also previous works that engendered moisture accumulation. - finally, a real effort of communication has been necessary to find compromises between low energy consumption, heritage preservation and the constraint budget. The school was inaugurated in 2017 and was the subject of several articles in the regional press. A visit was also organised on the occasion of the Heruitage Days in the same year.
Stakeholders Involvement
Public sector
Ville de Mulhouse - Pôle Education et Enfance
11 avenue du Président Kennedy 68200 Mulhouse
education-enfance@mulhouse-alsace.fr
Tel.( 33)3 89 32 58 72
Architect
Pierre Lynde, Formats Urbains Architectes Associés
39 rue de Victor Schoelcher 68200 Mulhouse
contact@formats-urbains.fr
Tel. 33 (0)3 89 33 27 90
Energy Consultant
IBEO
39 rue de Victor Schoelcher 68200 Mulhouse
contact@ibeo.fr
Tel. 33 (0)3 89 33 27 98
Tools used
Was the renovation process done following a specific methodology? No
Energy calculation The consumption for heat, domestic hot water, ventilation, lighting and pumps was calculated, before and after retrofitting, with a State approved calculation software. The software doesn't provide a dynamic simulation.
Hygrothermal assessment A dew point analysis was performed for walls.
Life Cycle Analysis (LCA) No life cycle analysis has been conducted.
Other BIM

RETROFIT SOLUTIONS

External Walls

Yellow sandstone and limestone rubbles

Yellow sandstone and limestone rubbles

The original exterior lime coating was progressively replaced with of cement coating in the eighties. To put things back the way they were before and prevent more moisture-related damages, cement coating was removed and replaced with lime coating. In the interior, plaster coating was also removed and 8 cm of mineral wool and a humidity-variable vapour-retarder were installed and recovered with plasterboards. A technical space between the vapour-retarder and plasterboards was designed in order to pass the electrical network but also to prevent the piercing of the vapour-retarder. Biobased insulation was first chosen, but mineral wool was finally used because it was cheaper. A dew point analysis (see picture) was performed for walls to validate this choice.

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U-value (pre-intervention) [W/m2K]: 3,0 W/m²K U-value (post-intervention) [W/m2K]: 0,34 W/m²K
More Details
Original wall build-up
Render - Ciment coating:
30 mm
Stone - Limestone and sandstone rubbles:
500 mm
Plaster - Plaster coating:
30 mm
Retrofitted wall build-up
Render - Lime coating:
25mm
Stone - Limestone and sandstone rubbles:
500 mm
Insulation - Mineral wool:
80 mm
Other - Humidity-variable vapour-retarder:
1 mm
Air gap - Technical space:
48 mm
Dry-lining - Plasterboard:
18 mm


Windows

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For cost reasons, only half of the windows was changed. There were already all double-glazed and some of them were replaced in 2010. The windows in bad state were replaced by wooden double-glazed windows with glazing bars. The others were repaired and adjusted and their seals were changed. The walls around the windows were not insulated because it was technical too difficult. So there are assumed thermal bridges between the walls and the windows.

The original single-glazed windows were replaced long ago. As there was no regulatory requirement on them, they were not replaced with identical ones. However, the windows are still in wood and with glazing bars.

Existing window U-value Glass [W/m2K]: 2,8 New window U-value Glass[W/m2K]: 1,4 Existing window U-value Frame [W/m2K]: 2,8 New window U-value Frame [W/m2K]: 1,4
More Details
Existing window type Casement window
Existing glazing type Double
Existing shading type NA
Approximate installation year 1980
New window type Casement window
New glazing type Double
New shading type Inner curtains
New window solar factor g [-] 0,5

Other interventions

ROOF

GROUND FLOOR

OTHER

MEASURES TO INCREASE AIRTIGHTNESS

ROOF

The attic floor was insulated by the interior with 26 cm of mineral wool. A vapour-retarder was installed between the insulation and the ceiling cladding. The attic floor is suspended to the roof with iron fittings. This is the traditional technique, dating from the 18th century. But it does not comply with fire safety and every iron fitting had to be shuttered with plaster and wood. To even more security, a fire detector was installed in the attic. The tiles dated from the thirties. Only the ones in bad state were replaced.

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U-value (pre-intervention) [W/m2K] 0.95 U-value (post-intervention) [W/m2K] 0.12
More Details
Original roof build-up
Other - Original wooden floor of the attic:
20 mm
Other - Wooden joist:
200 mm
Other - Old ceiling cladding:
20 mm
Retrofitted roof build-up
Other - Original wooden floor of the attic:
20 mm
Other - Wooden joist:
200 mm
Other - Mineral wool:
260 mm
Other - New ceiling cladding:
20 mm
GROUND FLOOR

The ground floor sits on a concrete slab. It was insulated with 8 cm of polyurethane and an underfloor heating was installed above.

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U-value (pre-intervention) [W/m2K] 1.7 U-value (post-intervention) [W/m2K] 0.35
More Details
Original groundfloor build-up
Concrete slab - Concrete slab:
200 mm
Finish - Old finish:
1 mm
Retrofitted groundfloor build-up
Concrete slab - Concrete slab:
200 mm
Insulation - Polyurethane:
80 mm
Other - Underfloor heating:
50 mm
Finish - New finish:
1 mm
OTHER

To prevent moisture accumulation in the lower sections of the buildings, a paved strip of 1 m 40 was managed between the walls and the bituminous surfacing of the backyard (see picture). Almost all the joists ends of the intermediate floors were mouldered. It was decided to completely replaced these floors (see picture). The new floors, consisting in hollow-care slabs, have several advantages : they have a better fire resistance, provide a better acoustic comfort and strengthen more effectively the structure than wooden floors. Because of the foundations that had subsided from several centimeters, concrete screeds were poured on the new intermediate floors in order to have a right horizontal surface. The peripherical edges of the new floors were not insulated so there are assumed thermal bridges between the walls and the intermediate floors. Thanks to the construction of the new building in the backyard, the canteen and the technical room were removed from the ground floor of the existing building. This resulted in a space saving and the school can now welcome 18 classes instead of 13 before. The interior design was also rearranged, in order to comply with the accessibility requirements. An elevator and new staircases were installed.

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MEASURES TO INCREASE AIRTIGHTNESS

The carriage entrance was very leaky. On the other hand, it was not used any more as an entrance for pupils. So the solution was to install in the inside a glazed door, more airtight, in front of the carriage entrance (see picture). An airtightness test was conducted, even if it is not required for French low energy building label for existing non-residential buildings, and lead to a good value, even lower than what is required for new non-residential buildings. To improve this value, some adjustments on windows and on the door giving in the attic were done. NB : the only available value was the French airtightness indicator Q4Pa,surf, which can not be converted in n50 without some other values, that are unfortunately missing.

Airtightness (pre-intervention) [ach@50Pa] 0 Airtightness (post-intervention) [ach@50Pa] 0

HVAC

HEATING

VENTILATION

HEATING

The technical room was shifted from the existing building to the new one. It shelters two condensing gas boilers of 224 kW each, that cover 200 % of the heating demand. This is a specific requirement of the city of Mulhouse, in case of failure of one of the boilers. A underfloor heating was installed in the entire ground floor. The intermediate floors are heated with new radiators. The cost of the reuse (checkup, cleaning, painting and storage) of the existing ones was judged too expensive. Temperature is being controled in each classroom by the city's technical services, to the nearest 0,1 degrees Celsius, thanks to a building management system (BMS). This BMS was also installed in the new building and energy consumptions of both buildings are monitored. The BMS needed several months to be fully operational.

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More Details
New primary heating system New secondary heating system
New system type Boiler Condensing
Fuel Gas Gas
Distribuition system Radiators Radiating floor
Nominal power 0 kW 244 kW
VENTILATION

There was no mechanical ventilation. Improving indoor air quality, even above the French regulatory standards, was one of the objective of the retrofitting. As natural ventilation hardly meet the regulation, a mechanical system was installed. Two dual-flow air handling units were installed in the attic (see picture) and the exhaust and air intake stacks were hidden in the new dormers. They are only functioning during the class hours, in order to save energy. In winter, the fresh air is filtered to eliminate fine particles, then preheated by the heat exchanger and a hot water battery and finally distributed all over the classrooms at a temperature of 21 °C. The air flow is calculated from the number of pupils in the classroom and the exhaust and air intake vents are located on both sides of the classroom to ensure an effective ventilation. In mid-seasons, the heat exchanger by-pass is activated and the fresh air is not preheated anymore.

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More Details
Original roof build-up New ventilation system
Type ventilation system Centralized
Type flow regime Cascade
Heat recovery Oui
Humitidy recovery No
Nominal power Unknown kW
Electric power 0,0 kW
Control system Yes

Energy Efficiency

Energy Performance
Energy performance certificate: The retrofitted school reaches the class B of the French energy performance certificate.
Voluntary certificates: The retrofitted school obtained the French low energy building ("Bâtiment basse consommation") label. To obtain this label, the consumption for heat, domestic hot water, ventilation, lighting and pumps must be calculated with a State approved calculation software and be lower than 40% compared to a calculated reference. The energy consumption detail can be find in the energy use section. It shows that heating is the largest energy user in the building, followed by ventilation.
Energy Use
Heating
Primary Energy 69 kWh/m2.y
Documents:
GE_T_P_3.jpg
Energy consumption of the building (author : Pierre Lynde)

Consumption_estimation_Before: 214 kWh/m2.y
Consumption_estimation_After: 69 kWh/m2.y

Primary Energy
Consumption_estimation_Calculation_method: Steady state simulation (e.g. EPC, PHPP)
Consumption_estimation_Before: 214 kWh/m2.y
Consumption_estimation_After: 69 kWh/m2.y
Measured Parameters
Internal Climate
Type_of_monitoring: Continuous
Description: The classrooms temperature and air flow are constantly monitored by the building management system and adjusted.

Internal Climate

Temperature

The classrooms temperature is constantly monitored by the building management system and adjusted. Overheating was reported at the end of the school year in 2017. The dual-flow air handling units were programed to provide a constant indoor temperature. This probably means that the windows were opened although they were supposed to remain closed for the good functioning of the units.

Indoor Air Quality

Improving indoor air quality, even above the French regulatory standards, was one of the objective of the retrofitting. Two dual-flow air handling units include fine particles filters and the classrooms air flow is constantly monitored by the building management system and adjusted.

Daylight

Visual comfort was also studied. Indirect lighting and white-coloured paints were favored in the classrooms. LEDs and presence detectors were also installed, as lighting is a major energy consumer in non-residential buildings.

Acoustic Comfort

Acoustic comfort is very important in a school. Acoustic suspended ceiling were installed both in the classrooms and in the circulations.

Costs

Financial Aspects

In the first version of the project, achieving the French low energy building ("Bâtiment basse consommation") label was not an objective. But thermal simulations showed that it was technically possible. Thanks to a grant from the Alsace Region and the French environment and energy management agency, the label was also financially achievable.

Running Costs
Lifecycle cost
No

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