The French demonstration object is a multi-storey building in Voiron, in the Isère Department. The building is made of concrete with no insulation. The windows are first generation PVC double-glazing 4-6-4. Natural ventilation. All dwellings have an individual gas boilers for the domestic hot water production, but each dwelling has its own,different heat production either electric heaters (c. 29 dwellings with an energy demand of 529 kWh/m²y) or fossil fuel boilers (c. 43 dwellings with an energy demand of 202 kWh/m²y). The building’s average consumption is 330 kWh/m²y.


Retrofit Concept

The retrofitting program will reduce the energy consumption down to 60 kWh/m²y (2012 French thermal regulation for new buildings) and create a structured heat and domestic hot water production through a collective heating system (gas boiler) and solar panels for hot water. Mechanical ventilation will be installed and the roof, floor and walls will be insulated. Furthermore, balconies will be closed using prefabricated elements.


Brief facts

Year of construction: 1961

Property type: Multi-storey building

No. of dwellings: 72

Project owner: OPAC38 (Office Public D'amenagement et de constroction de l'isere) , public/social housing company

Energy demand befor retrofit: 330kWh/m²y

Estimated energy demand after retrofit: 60 kWh/m²y

Construction works: November 2011-December 2012

Participating E2ReBuild partners: OPAC 38, SP Technical Research Institute of Sweden


Demonstration leader: Benoit Jehl, OPAC 38, benoit.jehl@opac38.fr


Tenant participation in Voiron

(December 2011)
Construction will be done with tenants staying in their apartments through the whole retrofitting process. This is why the owner, public housing organisation OPAC38, has to pay special attention to the tenants’ participation in the design and construction phase. 


Prefab difficulties and solutions

(December 2011)
As part of the E2ReBuild project the demo site Voiron tried to implement prefabrication as part of the retrofit work and a means to fulfil the objectives of the energy consumption reduction. OPAC38 first had in mind to use prefabrication panels all along the balconies, which will be closed and insulated to reduce the energy losses. However, due to fire and earthquake regulations, this would have meant that new foundations would have to be constructed to support the added structure.        
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Resin to strengthen the balconies

A thorough calculation however has shown that, due to incorrect placement metallic beams in the original building, the construction of the balconies was insufficient to support the extra weight. The adapted solution consists of the injection of a resin into grooves to strengthen the support of the balconies by the façade.To continue this work, OPAC38 had to recruit a company for the reinforcement of the balconies.


Injections of a resin into grooves of the balconies to strengthen the support to the façade.


Voiron near completion

(June 2013)
In the spring of 2013 construction work are being finalized with the mounting of the prefabricated wooden panels to close the balconies and create loggias.

National seminar: Thermal walk in Voiron

The local energy agency Agenda, organized, together with the municipality of Voiron and OPAC38, arranged a thermal walk in 28 February 2013. The walk was attended by 25 representatives of local stakeholders, other social housing company and cities' representatives.


E2ReBuild – Industrialised energy efficient retrofitting of residential buildings in cold climates. Contact info@e2rebuild.eu