Timber-framed house in Alsace, France

67370

Schnersheim, France

Owner

Malou et Denis ELBEL
67370 SCHNERSHEIM (FRANCE)

Architect

Claude Eichwald, maître d'oeuvre
5 route de Weinbourg - 67340 Weiterswiller
claude.eichwald@wanadoo.fr
(33)3 88 89 55 65

Contact Details

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

Other Information

http://www.rehabilitation-bati-ancien.fr/fr/retours-d-experiences/une-rehabilitation-energetique-et-une-restauration-patrimoniale-exemplaire

Visits
The owner is involved in a heritage protection association and often organises open house day for its members.

Related publications
The house is one of the case studies of the CREBA (French knowledge center for responsible retrofit of heritage building) website.
Schnersheim_Teaser_image
This timber-framed house is located in Schnersheim in the Alsace region (north-eastern France), near the border with Germany. It belongs to the same family since the 17th century and it has recently been retrofitted and restored. The project reaches a balance between low energy consumption and heritage preservation. The house is one of the case studies of the CREBA (French knowledge center for responsible retrofit of heritage building) website.
Energy performance
94 kWh/m2.y

Climate Zone Cfb

Altitude 184 m a.s.l.

HDD 3101

CDD 96

Protection level Not listed

Conservation Area:
No

Level of Protection:
None

Building age 1700-1800

Year of last renovation:
2010

Year of previous renovation:
2015

Building use Residential (rural)

Secondary use:
NA

Building occupancy:
Permanently occupied

Number of occupants/users:
2

Building area Net floor area [m²]: 350,0

Building typology:
Detached house

Number of floors:
2

Basement yes/no:
Yes

Number of heated floors:
2

Gross floor area [m²]:
350,0

Thermal envelope area [m²]:
875,0

Volume [m³]:
875,0

NFA calculation method:
SHON (fr)

Construction type
Timber frame

External finish:
Rendered

Internal finish:
Lime and clay coating

Roof type:
Pitched roof

+ MORE - LESS
Schnersheim_Overview - Photo credits: courtesy of Cerema
Schnersheim_Overview - Photo credits: courtesy of Cerema
Schnersheim_Aerial_view - Photo credits: courtesy of Cerema
Schnersheim_Aerial_view - Photo credits: courtesy of Cerema
Schnersheim_Cob - Photo credits: courtesy of Cerema
Schnersheim_Cob - Photo credits: courtesy of Cerema
Schnersheim_Framework © CREBA Rehabilitation-bati-ancien, Stratis
Schnersheim_Framework © CREBA Rehabilitation-bati-ancien, Stratis
Schnersheim_Painted_ceiling © CREBA Rehabilitation-bati-ancien, Stratis
Schnersheim_Painted_ceiling © CREBA Rehabilitation-bati-ancien, Stratis
Schnersheim_Stub © CREBA Rehabilitation-bati-ancien, Stratis
Schnersheim_Stub © CREBA Rehabilitation-bati-ancien, Stratis
Schnersheim_Picture_beginning_20th_century
Schnersheim_Picture_beginning_20th_century
Schnersheim_Mouldered_wooden_pieces - Photo credits: courtesy of Cerema
Schnersheim_Mouldered_wooden_pieces - Photo credits: courtesy of Cerema

RENOVATION PROCESS

Architecture

BUILDING DESCRIPTION

This house is located in Schnersheim, a village of 750 inhabitants, 20 km away of the head of the Alsase Region, Strasbourg. The house is a former farm, typical from this agricultural area named the Kochersberg, which long provided Strasbourg with wheat. The house is constructed on a light slope. The basement and two walls giving to the national road are in rubbles of sandstone and limestone. The storeys are timber-framed, filled with cob or hand-made bricks produced on site. It has a heated area of 350 m² on two storeys. The basement and the attic are not heated. The house is not listed : it is a simple farmer house, as thousands of others all accross the Alsace Region. But they are all being threathened with destruction, because they appear to most people as energy-consuming, not comfortable and difficult to retrofit. As the building is not located in a conservation area, the validation of the works by the Alsatian architectural review board was not required by regulation. But because the owner wanted to apply to a grant for exterior works related to heritage, a validation on these works was required anyway.
Urban context
The house is located in a dense village, at the edge of one of the major national road leading to Strasbourg. It is surrounded by other typical farms, built at the same time between the 17th and the 18th century.

HERITAGE SIGNIFICANCE

ELEMENTS WORTHY OF PRESERVATION
The house has been well preserved because it has been occupied through the centuries and maintained at a minimum. The cob was in a good condition. Finger marks of the people who filled the timber-frame were still visible 300 years after. The framework was also in good condition. There are three levels in the attic that were traditionaly used to dry tobacco. Some wooden beams have little holes in them, that served to their transportation by floating on the Kinzic river to the Rhine, from the Black Forest, in Germany, to Strasbourg. A painted ceiling from the beginning of the 18th century was also discovered in the attic. It was initially placed in the house, but was removed when it was judged old-fashioned! The "Stub", a living room entirely covered with wood panelling and where guests were received, was laid out in 1780. Unfortunately, some elements were missing. Pictures from the beginning of the 20th century helped the owner to restore these elements. The industrial tiles were replaced by traditional ones, called "Biberschwanz" (beaver tail). Five windows, filled with bricks during the 18th century because of a tax proportionate to the number of them, were also restored.
Heritage Value Assesment
The entire property has, as it is often the case in that region, the shape of a "U" : a yard surrounded by the farmer's house and several outbuildings that sheltered crops, horses and cattles and the farm equipment. In towns, many of these buildings were destroyed, either because they were in a state of ruin or to build new buildings. Indeed, land pressure resulting from the proximity of Strasbourg is a real danger for these traditional buildings. The basement, in which wine was stored, was built in 1717. This date is engraved in one of its pillar. An old account book, in possession of the family, also revealed that the timber-framed storeys were originally part of a timber-framed house built around 1730 and located 15 km away from Schnersheim. This date was also confirmed using dendrochronology by the owner. This house was purchased by the family, probably after a domestic fire, and remounted over the basement in 1783. It was not so rare, at that time, to dismantle a timber-framed house and to rebuilt it in an other location.
Heritage Assessment Files
Schnersheim_Account_book - Photo credits: courtesy of Cerema
Schnersheim_Account_book - Photo credits: courtesy of Cerema

State of repair

Conditions of the envelope
Before intervention, the house was in poor condition. Some damages were already well-known : - differentiel settlement of 12 cm throughout first and second floor. Indeed, in these traditional timber-framed houses, the kitchen was separated from the rest of the rooms by a stone-wall, called a "Brandwand", that was supposed to stop the spread of fire. In this case, the "Brandwand" was too heavy. - moisture problems in the basement. This is the consequence of several issues : sloping ground level ; use of cement coating and organic coating on the interior wall surface of the basement ; pour of a concrete slab on the basement floor ; lack of ventilation. After inspection, some of the wooden beams of the attic floor and some pieces of the framework were mouldered, probably due to a leak in the roof in the early 20th century. Wall plates from the second storey were also mouldered. Fortunately, those from the first storey were in good condition.
Description of pre-intervention building services
The house was never insulated before. A fuel boiler was installed in 1973 and a fuel tank of 3000 L occupied the basement. The heating distribution network was complex and corroded.

Aim of retrofit

Renovation
The retrofitting project lasted from 2010 to 2015. The owner wanted to restore his house to its original condition, but also to retrofit it and to obtain a low energy label. One particular objective was to prove, by a real example, that it is possible to live in that kind of heritage buildings with all modern conveniences. Retrofitting these buildings is also a answer to urban spread, very present in the region. Finally, the owner wanted to support the local craftspeople that are still working on heritage buildings (joiner, brick maker, traditonnal stove maker, carpenter, cabinetmaker) and the local materials (lime, naturel pigment, wood pellets). The owner is involved in a heritage protection association and often organises open house day for its members. The retrofitting and the restoration of the house are well admired, but are not considered as entirely replicable on other houses of the same type, because the owner spared no expense on the works. However, the solutions that were chosen for each element are inspiring and can be easily adapted to other houses.
Lessons learned
The owner had to convince a lot of people that it was possible to retrofit an heritage building like his : - The first architect that he hired declared that it was not possible to insulate his house with lime-hemp. - The architectural review board in Alsace was sceptical about double-glazing windows made to measure, until he saw the prototyp. - Many people thought that creating a technical room by underpinning was impossible.
Stakeholders Involvement
Private Sector
ELBEL Malou and Denis
Non applicable
Architect
Claude Eichwald, maître d'oeuvre
5 route de Weinbourg - 67340 Weiterswiller
claude.eichwald@wanadoo.fr
Tel.(33)3 88 89 55 65
Conservation Consultant
Jean-Christophe Brua, atelier d'architecture JCBA Sarl
22 rue La Fayette 67100 Strasbourg
contact@jcba.fr
Tel.(33)6 87 41 42 09
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, basement ceiling and attic floor.
Life Cycle Analysis (LCA) No life cycle analysis has been conducted, but most of the materials that were used are biobased and not made from petrochemical products.

RETROFIT SOLUTIONS

External Walls

Timber-framed walls filled with cob and bricks

Timber-framed walls filled with cob and bricks

12 to 18 cm of lime-hemp concrete was sprayed on walls. A dew point analysis was performed for walls, as well as for basement ceiling and attic floor, to validate the choice of this insulating material. The project team was aware that the post-intervention U-value was not as good as it should be, but decided to compensate on other elements. Lime-hemp concrete was chosen because it is permeable to vapour and that it has so a similar behaviour to cob. Besides, lime-hemp concrete increases the sensation of comfort of the occupants, what was one of the objective of the owner. To avoid air leakages and thermal bridges, the flooring from the second storey was removed in order to spray the lime-hemp concrete in a continuous way through the storeys. Some pieces of the wooden-frame were missing because they had been sawed for convenience, to install a window for example. They were reinstated to prevent structural damages. The "Brandwand", that caused the differential settlement because it was too heavy, was replaced by a timber-framed wall, filled with lime-hemp concrete and a with a steel beam on its top. The whole structure was cut by 7 tonnes. To prevent an other structural damage, a reinforced concrete footing was poured in the basement. There differentiel settlement of 12 cm is still visible but the structure has been stabilized.

There was no painting on walls or other elements to preserve and the "Stub" has been repositionned after the works. So there is no real issue about the conservation compatibility, although the lime-hemp concrete is not a reversible intervention. The interior render was coloured with natural pigments from the local lime-burner. The plastic coating and the exterior organic render were removed, as the multiple layers of wallpaper and interior coating. No tiling and no wallpaper were put on the new interior lime render, to let vapour freely transit through the walls. The walls are indeed permeable to vapour from the exterior to the interior, thanks to the materials that were used.

U-value (pre-intervention) [W/m2K]: 1,75 W/m²K U-value (post-intervention) [W/m2K]: 0,39 W/m²K
More Details
Original wall build-up
Plaster - Plastic coating and exterior organic render:
20 mm
Other - Timber-framed filled with cob and bricks:
160 mm
Other - Multiple layers of wallpaper and interior coating:
20 mm
Retrofitted wall build-up
Other - Multiple layers of wallpaper and interior coating:
20mm
Other - Timber-framed filled with cob and bricks:
160 mm
Insulation - Lime-hemp concrete:
180 mm
Plaster - Interior lime render:
20 mm


Windows

Double-glazed wooden windows dedicated to heritage buildings

Double-glazed wooden windows dedicated to heritage buildings

All the original single-glazed wooden windows were replaced by double-glazed ones. Thanks to pictures from the beginning of the 20th century, it was possible to restore the windows as they were originally. The doors were replaced by more traditional ones. The outside shutters are the original ones. A loggia was created in the second storey by removing cob from timber-frame and installing a double-glazed fixed window against the interior surface of the wall. This brings light to the house, knowing that these traditional houses are often depreciated because of their lack of light. The windows are all in oak and some are arched. They are made of four casements that can be opened independently.

The windows were all replaced, but the new ones are identical to the original ones, except the glass, which is a double-glazing dedicated to heritage buildings. The windows were made to measure by a local joiner. This was the only exterior work related to heritage for which the Alsatian architectural review board, charged for validating these works not by regulation but because of a grant application, had to be convinced. They thought indeed that double-glazing, even dedicated to heritage buildings, would be too thick and that it would be impossible to maintain the original proportions of the windows. So the owner and the joiner had to produce a prototyp, that finally convinced the board.

Existing window U-value Glass [W/m2K]: 4,0 New window U-value Glass[W/m2K]: 2,14 Existing window U-value Frame [W/m2K]: 2,14 New window U-value Frame [W/m2K]: 4,0
More Details
Existing window type Casement window
Existing glazing type Double
Existing shading type Outer shutter
Approximate installation year 1970
New window type Casement window
New glazing type Double
New shading type Outer shutter
New window solar factor g [-] 0,5

Other interventions

ROOF

GROUND FLOOR

OTHER

MEASURES TO INCREASE AIRTIGHTNESS

ROOF

The tiles were replaced by traditional ones, called "Biberschwanz" (beaver tails). A rain screen, that was not originally present, was installed. The roof windows were replaced by dormers, which shape is more traditional. Modern roof vents were also replaced by more traditional ones in copper. After installing a vapour retarder, the attic floor was insulated with about 9 cm of granulated cork (in order to get the floor horizontal) and with two cross-coats of wood-fibre panels of 10 cm. The top of the stairwell was insulated with 20 cm of granulated cork and 4 cm of woodwool.

Original details like dormers were restored. Others interventions like installing a rain screen or insulating the floor of the attic are invisible to the occupants and reversible. Therefore, there is no issue about conservation compatibility.

U-value (pre-intervention) [W/m2K] 0,95 U-value (post-intervention) [W/m2K] 0,16
More Details
Original roof build-up
Other - Original wooden floor of the attic:
20 mm
Other - Wooden joist:
200 mm
Retrofitted roof build-up
Other - New wooden floor of the attic:
25 mm
Other - Wood-fibre panels:
100 mm
Other - Granulated cork:
90 mm
Other - Vapour retarder:
1 mm
Other - Original wooden floor of the attic:
20 mm
Other - Wooden joist:
200 mm
GROUND FLOOR

The basement is only located under a half of the first storey. Before retrofitting, there was a lot of moisture in the basement, because of : - the use of materials which were not permeable to water vapour, like concrete ; - the lack of ventilation ; - a naturel high moisture load due to the location of the house on a light slope. The basement concrete slab was removed and replaced by different layers of pebbles and sand to ensure drainage. A new flooring with reused terracotta tiles was created. The joists of the floor separating the basement from the first storey were mouldered because of the high moisture load of the basement. They were replaced and the floor was insulated between the new joists with 13 cm of lime-hemp concrete. Where there was no basement, a technical room was excavated by underpinning in order to shelter the boiler, the pellet silo and the ventilation system. The new floor consists in a reinforced concrete slab and a lime screed with expanded clay balls. The first storey is covered with parquet or with traditional flooring of wood and reused terracotta tiles.

Original details like the traditional flooring were restored. Others interventions like installing the ventilation system or insulating the floor are invisible to the occupants, but not really reversible because of the concrete and the screed. Therefore, there is no real issue about conservation compatibility.

U-value (pre-intervention) [W/m2K] 0,95 U-value (post-intervention) [W/m2K] 0,4
More Details
Original groundfloor build-up
Floor joists - Wooden joist:
200 mm
Finish - Parquet:
20 mm
Retrofitted groundfloor build-up
Floor joists - Lime-hemp concrete between joists:
200 mm
Finish - Parquet or traditionnal flooring:
30 mm
OTHER

The house is constructed on a light slope. In order to reduce the water pressure on the highest external wall and to lower moisture load in the basement, a gutter was dug and paved at the exterior side of the wall.

There is no issue about conservation compatibility.

MEASURES TO INCREASE AIRTIGHTNESS

The heated envelope was clearly defined in order to avoid air leakages. The central stairwell, that goes from the basement to the attic, is separated from the basement by double-glazing bay windows and by a door from the attic. Besides, the intermediate floor was dismantled in order to realize complete hemp-lime concrete spraying, avoiding thermal bridges and air leakages between the floors. Despite taking all possible care, the wooden joists and the heating distribution network between the technical room and the first storey were still not perfectly airtight.

Airtightness (pre-intervention) [ach@50Pa] 5 Airtightness (post-intervention) [ach@50Pa] 2,04

HVAC

HEATING

VENTILATION

DOMESTIC HOT WATER

HEATING

A 25 kW pellet boiler of an efficiency of 95 % was installed in the technical room. It provides heating and domestic hot water thanks to two storage tank (300 and 800 L respectively). The pellet silo is also stored in the technical room. The worm screw usually used to convey pellets to the boiler was replaced by an aspiration system. Indeed, worm screw can cause ignition and the owner did not want to take this risk in a timber-framed house. At the beginning of the project, a geothermal heat pump was first considered but rapidly abandoned because of the high cost of it and technical issues. A traditional stove, called "Kachelofe", was installed in the heated envelope as an additonal heating. This kind of stove was the principal heating system in Alsatian houses before the 20th century. It is supplied by logs and takes its air supply directly from the outside. The owner did not want to have imposing radiators in his home, so he opted for an innovative distribution system by baseboards.

The boiler, the pellet silo and the storage tank are installed in the technical room. The stove is a traditional one. The distribution system is hidden in the baseboards. Therefore, there is no issue about conservation compatibility.

More Details
New primary heating system New secondary heating system
New system type Boiler Stove
Fuel Biomass Biomass
Distribuition system Radiating baseboards No distribution system
Nominal power 25 kW kW Unknown kW
VENTILATION

A balanced ventilation with heat recovery was installed in the first storey and a simple mechanical ventilation in the first storey. The air exchange unit was installed in the technical room, where the temperature is always higher than 20 °C in winter. The owner did not want to see the exhaust and air intake vents on the roof, so he hid them behind shutters and near an exterior staircase. The ventilation distribution system consists in smooth semi-flexible conduits. A maintenance contract was signed between the owner and the ventilation system supplier : the conducts will have to be cleaned every 4 years and the filters changed every 6 months. The owner also wanted the ventilation distribution network to be invisible. So the air supply units were installed between the joists and covered with lime-hemp concrete and the air extract unit in load-bearing walls or even in pieces of furniture. All these units where made to measure and were placed in order to guarantee a good flushing of the air. In order to avoid a high moisture load in the basement and in the technical room, the windows are always opened in summer. In winter, they are closed but a simple mechanical ventilation is turned on.

The ventilation system is installed in the technical room. The ventilation distribution system is hidden in load-bearing walls, pieces of furniture or covered with lime-hemp concrete. The exhaust and air intake stacks are hidden behind a shutter and near an exterior staircase. Therefore, there is no issue about conservation compatibility.

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

See above

See above

More Details
New DHW system
Type with heating system
Hot_water_tank Yes
With heat recovery No

RENEWABLE ENERGY SYSTEMS

Biomass

Biomass

The boiler uses pellets and the traditional stove logs.

Non applicable

More Details
Biomass System
Type
Storage size
Origin of biomass
Overall yearly production 0,0 kWh

Energy Efficiency

Energy Performance
Energy performance certificate: The retrofitted house reaches the class B of the French energy performance certificate.
Voluntary certificates: The retrofitted house 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 104 kWh.m2.year in primary energy.
Energy Use
Heating
Primary Energy 94 kWh/m2.y
Consumption_estimation_Before: 352 kWh/m2.y
Consumption_estimation_After: 94 kWh/m2.y

Primary Energy
Consumption_estimation_Calculation_method: Steady state simulation (e.g. EPC, PHPP)
Consumption_estimation_Before: 352 kWh/m2.y
Consumption_estimation_After: 94 kWh/m2.y

Internal Climate

Temperature

On a hot day (36 °C at the exterior), with shutters and windows closed, the interior temperature was 25 °C at midday.

Daylight

The glazed loggia brings light to the house, knowing that these traditional houses are often depreciated because of their lack of light.

Costs

Financial Aspects

The owner spared no expense on the retrofitting of his house. The energy retrofitting awarded a regional grant of 10 000 €, according by the Alsace Region and the main electricity supplier in Alsace. The grant also paid the airtighness tests and the visit of a building control office. The restoration obtained a national grant that funded 1 % of the total costs of the exterior works related to heritage (tiles, roofs, framework, exterior render, etc) and that allowed the owner to get a tax credit amounting 25 % of these costs. As the building is not located in a conservation area, this was the only works were the validation of the Alsatian architectural review board was required.

Investment Costs

Cost of energy related interventions:
150 000 € (pre-tax prices) (total)
Amount includes: The whole energy retrofitting of the house costs 150 000 € (pre-tax prices). It includes labour and supplies. It does not include either the restoration costs or the windows, made to measure. To this is added a 280 €/year (pre-tax prices) maintenance contract for the balanced ventilation and a 216 €/year maintenance contract for the heating system. 50 % of these costs was for the heating and domestic hot water system ; 17 % for the walls insulation with lime-hemp concrete ; 15 % for the ventilation system.
Running Costs
Total annual energy cost
With a 9 tonnes pellets consumption, the annual heating cost amounts to 2500 €. (total)

Lifecycle cost
No

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