[REX] EnergieSprong rehabilitation with green gas of 99 rental units

[REX] EnergieSprong rehabilitation with green gas of 99 rental units

The Savoie OPAC, a major social landlord in the Auvergne-Rhône-Alpes region, is undertaking the energy renovation of its social housing stock. With 6,300 homes to renovate, the landlord is looking for an efficient and replicable model to eliminate thermal sieves.

The MASSIRENO ENERGIESPRONG renovation project of 2 buildings in Montmélian (73) illustrates this desire. In addition, the lessor has chosen to opt for green gas, in a strategy of seeking a virtuous local energy mix. This is the first project to integrate biomethane as part of an ENERGIESPRONG renovation. Feedback with Philippe Marteel, Heritage Manager of the OPAC de la Savoie.

An ambitious renovation on an occupied site thanks to the EnergieSprong approach


As part of the recovery plan developed to deal with the health crisis, the MassiRéno call for projects launched in December 2020, aimed at the massification of the renovation of rental housing in France. The Savoie OPAC applied for two of its buildings and was named the winner, thus benefiting from financial aid of more than 1.5 million euros . However, the Savoie OPAC wanted to go further than the specifications in order to anticipate the increasing requirements of environmental regulations.

From this perspective, the EnergieSprong approach appeared to be the most relevant. This European movement, launched in 2012, "works to democratize access for as many people as possible to high-performance, rapid, qualitative, attractive and comfortable renovations, by relying in particular on new methods of industrializing renovation, and on a specifications based on requirements of results rather than means" ( source ). The two buildings in Montmélian corresponded to the EnergieSprong criteria: no balconies and a smooth cubic shape. Helped by the company Greenflex , the lessor appointed the 3S CONCEPT Project Management Assistant with a view to consulting the design, construction, operation and maintenance market. The consortium led by CAMPENON BERNARD was selected.

As part of the renovations, more than 5,000 m² of ITE facades will be insulated with PANOBLOC ( Techniwood ) panels, fitted beforehand in the factory, with joinery, embrasures, concealments and exterior facings. This triple performance wood construction solution is more expensive than a classic ITE facade, but is more durable and requires less maintenance over time . In total, 579 m3 (i.e. 33 kg/m² in actual quantity) of biosourced materials were mobilized for the work.

To improve the quality of life of the tenants , the lessor chose to install balconies. The latter also serve as shadehouses, thus improving the summer comfort of the accommodation. For winter comfort, the entrances have been equipped with thermal locks to reduce losses. In general, for this project, the lessor favored techniques, materials, more expensive elements but with lower maintenance requirements. The work is therefore part of an overall price concept and a long-term vision.

The work is entirely carried out on an occupied site. To facilitate the operation, a general contractor is present on the site during theentire site in order to establish a constant dialogue between tenants and contractors . A dedicated website and telephone line are also available. Thus, interventions can be better adapted to tenants' activities, which reduces delivery times. It only takes between 8 and 10 days per accommodation to undertake all the work! In addition, the Energiesprong approach provides support for residents after the works, thus raising their awareness of new energy systems.

The choice of biomethane


Energy choices are another interesting aspect of the project. For these two buildings, the most important energy consumption item was heating, provided by natural gas boilers in very good condition. Initially, the OPAC planned to use wood pellets for this position, the resource being abundant in the region due to the presence of a nearby sawmill. However, the lessor crossed paths with GRDF, which was able to present its biomethane boiler solutions. The lessor finally chose this proposal because it makes it possible to keep the existing boilers, while dividing the consumption dedicated to heating by 4 . This will also make it possible to include the operation in the deployment of a local and resilient energy strategy . In Savoie, 10 renewable gas production projects are the subject of implementation studies in order to support the development of a more virtuous and more resilient energy mix in the face of climatic, political, health and economic hazards.

Development and advantages of green gas

Unlike natural gas, green gas is a renewable resource with a limited environmental impact (44geqCO2/kwh - carbon base) obtained through the recovery of agricultural waste or wastewater. These are converted into gas through methanation, methanation or hydrogen.

The potential for green gas production by 2050 is 420 TWh; which would cover 100% of uses. In addition, green gas can be injected directly into the existing network, thus reducing the investments required and the pollution generated by the construction of new infrastructures.


The lessor is pursuing the objective of rehabilitating quasi-passive buildings - the weather conditions in the region make it difficult to achieve the level of positive energy. For this, photovoltaic panels have been installed on the roofs for an area of more than 350m². Over their first 5 years of life, they will produce approximately 91,500 kWh.year, electricity then resold to participate in the financing. In the end, all-purpose consumption will reach 55.5 kWhEF/m² SHAB.year!

A replicable model


Savoie is a territory in strong development, especially around the towns of Chambery and Aix-les-Bains. OPAC73 manages 22,000 housing units in Savoie and in particular their maintenance and their thermal and technical renovation. In 2021, the investment for these positions represented approximately €60,000 per dwelling. This building stock includes a significant number of buildings with unfavorable DPEs (E, F, G); in particular due to the heating needs at altitude and the sometimes high temperatures in summer. And this, even for buildings that have already been renovated! But above all due to the weighting coefficient of 2.3 between primary energy and final energy on electricity consumption, energy almost systematicallyused on buildings in winter sports resorts to cover heating and domestic hot water needs.

These factors prompted the lessor to commit to a strong sustainable development policy. For this, a 10-year action plan is being drafted. The project presented in this article aims to implement one of the foundations of this strategy: to design a comprehensive and efficient energy renovation model that reduces maintenance needs over the long term and has the potential to be reproduced on the entire park . In addition, there is an economic aspect to this, through the objective of controlling the increase in rental charges due to the works. With 6,300 homes affected, the stakes are high.

This project will be delivered in September 2023 and will pave the way for the rest of the lessor's fleet. The model will be easy to replicate once the companies, materials, techniques, devices have been identified. The objective is also to extend the use of biomethane for heating and producing hot water in homes!

Article written by Mariette Guermonprez - Construction21, The editorial staff

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  • Ludovic GUTIERREZ

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