Case Study: Construction of 10 semi-detached houses in La Brède (3 662 inhabitants)

Short Description

Key Elements

Main Results

This project was one of the first BBC certified operation. As a consequence, the construction site was a pilot in terms of companies and craftsmen training related to energy performances. As a pilot, some of the technical solutions selected proved not to be adapted to the context and the global cost revealed to be 13% higher than regular operations. In the new projects, these solutions are now avoided. This is the case for example of the mechanical ventilation with heat recovery. Due to the costs (investment and maintenance) and the complexity of this system, this solution revealed not to be conclusive. Throughout the conception phase, architects were very involved in the project and worked closely with the energy engineering consultant company.

In terms of performances expected, at the end of the first year, a gap appeared between the targeted consumptions and the real consumptions. As a consequence, the follow-up of these consumptions is very important to be able to react. Indeed, during that first year, due to the good insulation and the important solar inputs, the temperature in the dwellings appeared to be too high.

A good acoustic quality was obtained thanks to the structure and the walls composition.

Lessons learned

Among the weak points of the project, some of the technical solutions appeared not to be optimal, for example the mechanical ventilation (high costs, use and maintenance complexity) but also the solar thermal energy. As a matter of fact, the solar production (1600kWh/yr.dwelling) equals a gas consumption of 85€/ yr.dwelling. Considering the extra investment cost of 3500€/dwelling and the extra maintenance cost of 90€ (which does not include the cost of cleaning of the solar panels), the financial benefit is not reached. One of the reasons for these choices could be that the maintenance feedbacks were not considered during the conception phase. Some other solutions were studied in the pre-studies but were not selected (for example the ground-coupled heat exchanger).

Among the strong points of the project, the joint work between the architects and the energy consultants enabled to reach a good level of performance. Even if all the solutions did not prove to be optimal, most of the technical choices were adapted to the context and took part in the global quality of the buildings.