Study "Ancient habitat in Alsace, energetic improvement and preservation of heritage"

These buildings are in fact different from those of the period 1949-1973, being in general less energy consuming and presenting a very different hygrothermal functioning.

The State Consulting Study is freely downloadable.

The renovation of the existing building stock is a major challenge to achieve the objectives of lower energy consumption and greenhouse gas emissions:

• in 2012, nearly 45% of the final energy consumed in France comes from residential and tertiary, down to 38% in Alsace, of which 25% comes from housing alone.

As part of the Plan de rénovation énergétique de l'habitat, the Alsace Regional Directorate for Environment, Development and Housing (DREAL) and the Alsace Regional Directorate for Cultural Affairs (DRAC) have launched a study "Ancient habitat in Alsace: energy and heritage".

This study is freely available via sheets and reports to download freely opposite:

• eight cards (general method and one sheet by type of frame studied);
• technical reports;
• a state of the art of renovation practices.

Published in two phases, "Comprendre" (September 2014) and "Agir" (September 2015), the study "Habitat ancien en Alsace: énergie et patrimoine" was conducted by CEREMA-Est and the architecture firm Oziol-De Micheli, in association with all local partners involved in the energy renovation of buildings.

A thermal typology of the building before 1948 was first defined in Alsace. Seven representative dwellings were selected, instrumented and studied (physical parameters, hygrothermy) for seven months:

• the adjoining apartment of the suburbs
• the apartment in adjoining report building
• the so-called master house built of bricks
• the independent masonry house
• the masonry dwelling house in a farmhouse
• housing in a half-timbered farm building
• the half-timbered house with schlupf

These observations made it possible to model seven standard housing units using thermodynamics software, on which a large panel of energy renovation actions was tested and compared.

Different insulation materials were compared (benefits, risks, costs).  Three renovation scenarios were proposed for each type, and evaluated according to five criteria: energy savings, summer comfort, reduction of the cold wall effect in winter, absence of risk related to humidity in the walls, respect for the heritage and architectural aspect. Construction costs were estimated, both in terms of profitability and sustainability, and compared to the cost of inaction in euros and tonnes of CO² not emitted.

The study reveal the qualities of the old Alsatian building before renovation:

• energy label close to or even above the national average, which represents rather good thermal performance given the harsh local climate;
• very good summer comfort, due to its good inertia, almost absence of thermal bridges, hygrothermal balance;
• buffer-spaces (cellars, shed, etc.) and "Schlupf" (empty spaces about 80 cm wide between the houses) to the beneficial role from the thermal point of view.

The study demonstrates the good results in terms of energy savings achieved by the work:

• a major energy improvement (BBC-renovation) can be achieved while respecting the main characteristics of the facades, roofs and carpentry.
• Other approaches are also possible to gain one or two classes of energy label, by favouring other criteria: limiting costs, acting in stages or favouring a more complete preservation of the heritage and architectural quality of buildings.
• The study also shows that the proper maintenance of the building and the limitation of air leakage is in itself an effective action.

The study highlights points of vigilance:

• Energy renovation actions impact summer comfort, more or less significantly depending on the scenarios;
• the installation of external thermal insulation has a significant impact on the architectural aspect of the old structure (in the study, this solution was tested only in one particular case); the installation of an external insulating coating is sometimes possible;
• the conservation and/or improvement of existing windows and doors is almost equivalent to their replacement from an energy point of view when the walls are insulated, allowing to reconcile performance and complete preservation of the architectural value of the facades;
• The choice of insulation and the quality of its implementation are essential to preserve the initial hygrothermal balance of the old walls;

To conclude, the study highlights that the approach to energy renovation of old buildings must be multi-criteria.

This work was carried out in partnership with many stakeholders in the territory:

Alsace Regional Council, Departmental Councils of Bas-Rhin and Haut-Rhin, Eurometropole of Strasbourg, Mulhouse Agglomeration Community, CAUE 67 and 68, ADEME, Points Rénovation Info Service, Parc naturelles régionaux des Vosges du Nord et du Ballon des Vosges, Pôle de compétitivité Énergivie-Fibres, Caisse des Dépôts, FNAIM, Bailleurs sociaux, FFB, EDF,CAPEB, ASMA/MPF, Ordre régional des architectes, AART-A.

1Source: ASPA 14040401-ID, version of 19.05.2014