The whole with costs of construction increased by 5 to 10

The (sur) is the green building certification cost For the past five years, sites multiply under the banner HQE, the BBC, Breeam or LEED (see opposite) labels. Report buildings, offices, housing, schools, cultural facilities: the wave of sustainable real estate is sweeping across the Hexagon, with 15,000 buildings in labelling BBC Effinergie. The whole with costs of construction increased by 5 to 10.

Yet, the pioneers do not systematically the same observation, as shown by several studies in recent months. Economists of the national Research Council (NRC) spent through the performance of 100 American buildings LEED certifications. Unsurprisingly, the researchers calculated that most of these structures consume on average 18 to 39 less energy per square metre than their conventional counterparts. But between one quarter and one third of them are in fact more than their counterparts not certified. Perish for investors who undertake incremental costs to acquire a better building. The study said even that the performance of the building are décorrélées conversions LEED notes (silver, gold, platinium).

France, the exercise has to be led by a team composed of the real estate land Icade and the scientific and technical building Centre (CSTB). Icade is part of the masters of book pioneers in the HQE with the "270" building in Aubervilliers (Seine-Saint-Denis), delivered in 2005. The authors of the study, funded under the Programme of research and experimentation on energy in the building (Prebat), interviewed at length users and managers of three tertiary buildings: the 270 and Millennium, both located in Aubervilliers and Icade, and the visitor's of the Institute of research, Ineris in Verneuil-en-Halatte (Oise).

Disappointing results

These three buildings shared ambitious reduction targets. Experience shows that the two buildings of Icade missed their target energy. The actual consumption of the 270 reached 170 kWh/m a year, 50 kWh/m a year more than forecast. In 2008, Millennium consumed 247 kWh/m2, against 217 kWh/m2prévu. Compared to the RT 2005 standard, the gain is low, or zero, but it is advantageous to the existing Park, Ademe estimates the average in 286 kWh/m2 per year.

The ground survey to better understand the origin of these excesses. In the case of the 270, it is the case of a poor match between the design of the building and its use. Designed to work day, it is in fact occupied also the night, as one of the tenants has worked in the press ("Paris-Turf"). At the time, heating and air conditioning are never sleep modes provided. "Thought in logic disposability, the building was not designed to adapt to a different use to each plateau", diagnostic study.

The building operators also say run on excessive sophistication of the technical management of the building (GTB) computer, new edition of home automation of 1980s syndrome. The occupants are competing stories: presence sensors trigger capriciously lighting. Robotic stores, in addition to engine reliability problems, have been disabled by employees holding too noisy operation. The large glass, facades planned to exploit the natural light and improve the comfort of life, obstruct OA work on screen. Users have therefore preferred the artificial lighting and clogging the Bay Windows, sometimes by Additionaly cartons. Unable to open the window interferes with employees, who complain of bodily odors day. As the storm water recovery system, it has never connected to double existing network. Even the excellent acoustic insulation of the offices is experienced by some as a disturbing cut.

The flag of the Ineris, him, home consumes slightly less than expected, with the simplicity of its passive devices design. Some defects persist, as under-design of water-saving toilet flushing, which imposed their judgment. The lobby is poorly heated and requires radiators of make-up in the winter. In summer, night ventilation, which operates the thermal inertia of the building, found its limits in the high floors, because security issues prevent the opening of the doors of Office, essential to the system. In addition, this system was arrested the night by security agents that do not support the induced air currents. "If the building does not meet the basic needs of the users, then it is illusory to hope for a more sober behavior on their part", warn the authors.

Lack of expertise

The Canadian study succeeds to the same conclusions for the drift of some buildings: changes in use and excessive sophistication of technologies. One.

These tendencies are well-known specialists in sustainable building. Alain Bornarel, Office of specialized studies tribe, also recalls the existence of errors of design and construction, particularly due to the lack of know-how of French artisans in the airtightness. He cited the case of a tertiary project which provided a ventilation double flow system. A few months after the receipt, the contracting authority finds that its energy consumption are twice higher than planned. "The contracting authority and the Office had decided, for reasons of cost and ease of maintenance, remove the system heat exchanger," he smiles. So, Alain Bornarel keeps well to berate the mistakes of youth in sustainable construction: "I claimed the right of experimentation and innovation." Follow the early life of a building on 2 or 3 years to stabilize its performances. Indeed, experience has not deterred Icade to continue its acquisition of 250.000 m of buildings certified HQE.