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The quiet revolution in the energy performance of buildings

All around the world, construction methods have begun an accelerated shift towards increased innovation and efficiency, whether in building design, the implementation of constructive solutions, or the distribution and placement of building materials. One dimension of this revolution is the energy efficiency of buildings. Insulation solutions, in particular, are undergoing an unprecedented wave of innovation.

March 2016
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lire en français
Executive Resume

Today, we are witnessing a profound reversal of the trend toward decreased productivity and a low rate of innovation that obtained in the construction industry for over a quarter of century. From the late 1960s to the early 2000s, this relative decline of productivity in construction was manifest in a number of countries, including the United States. Over the last fifteen years, the governments of many developed countries have tried to address the problem by adopting strategies to support innovation and productivity gains in the sector.

Dynamic innovation

The increasing use of information technologies plays a key role in these strategies. For example, Building Information Modeling (known by its acronym BIM) allows for the optimization of design, construction and maintenance, and it is gradually becoming mandatory for all public contracts. The understanding of innovation and mechanisms for the diffusion of innovations in the construction sector has made significant strides in recent years and is providing support for the development of more effective public policies. At the same time, companies in the industry have pursued their movement towards consolidation and increased their investment in R&D in varying proportions on the basis of this extended activity.

Although relatively recent, this movement is beginning to be perceived by the general public, and this is leading in turn to increased demand for innovation and improved performance in construction and renovation, especially in the energy field. In a recent French poll on the most innovative professions, engineers in the building industry ranked in fifth place and architects in seventh. This increasing perception of the sector’s innovation potential is also reflected in demands by end users in construction or building renovation, even as their decision-making power is growing thanks to information technologies.

In regards to their selection criteria, it is giving rise to an ever-increasing demand for comfort:  for example, in terms of visual, thermal, acoustic or air quality. These new demands are supplementing traditional quality requirements, deadlines and sector-wide competitiveness. Given the growing power of end users in the decision-making chain, the dissemination of innovations is being further accelerated by the fact that they can ensure that a quick gain in comfort is understandable, measurable and guaranteed. To take an example of an application that is growing quickly: high sound absorption ceilings are undergoing exponential growth, because, as numerous scientific studies show, they significantly increase the cognitive and academic performance of students, not to mention business productivity or the quality of care in hospitals.

Energy performance

Of course, the demand for innovation and improved performance is growing particularly quickly with respect to energy performance. There have been numerous recent innovations that result in significant gains in terms of energy efficiency, especially in the field of insulation.

The insulation performance of glass wool has improved by 20% in barely ten years, while at the same time offering the best guarantees for health and environmental protection. New generation glass wool includes variable proportions of bio-based materials. And for constrained environments where the installation of mineral wool is difficult, manufacturers are working on super-insulating materials, particularly vacuum insulated panels (consisting of a core material confined in a tight film and placed in a depression) or silica aerogels that should be available in a few years. The latter, composed of a very light amorphous silica structure, contain over 95% air captured in nanometric pores.

But energy efficiency is not simply achieved by using the best insulators: The physical properties of construction materials, the design of systems and automated controls, and active systems all also play a role. Research is very active in each of these fields. For example, air-sealing and thermal bridge-breakers are now mandatory in France under the current thermal regulation (RT2012), which promotes the use of increasingly complex coating systems or membranes. A good airtightness serves to limit losses, optimize VMC yields, control the quality of indoor air, and protect building interiors by eliminating the risk of condensation. Solutions include waterproofing membranes for walls and roofs (hygro-regulating properties) and internal gypsum-based technical coatings for masonry walls.

The use of increasingly large glass walls also reduces lighting needs while increasing visual comfort and mitigating heat loss: The thermal transmittance of the latest generation triple glazing is four times lower than that of the ordinary double glazing that came on the market barely fifteen years ago. Electrochromic glass developed by the US company Sage allows for color modulation using a simple electrical control, optimizes solar gain and significantly reduces air conditioning needs.

Among other active solutions, one can also mention the popularization of dual flow ventilation systems and  heaters with open window sensors. Manufacturers are working on applications of phase change materials that can help regulate the indoor temperature of buildings to reduce the need for air conditioning and heating. Finally, to test the effectiveness of all these systems in situ, companies are multiplying the use of demo installations: Co-sponsored by Salford University, Leeds Metropolitan University and Saint-Gobain Recherche, the “Energy House” in the UK is an example of renovation done in a controlled environment. It is the most successful demonstrator to date of domestic energy renovation. Some of these demo installations are open to the public.

The dissemination and development of these technologies will enable significant energy savings in small energy efficient building complexes, such as exist in most European countries. French building stock is no exception and some figures are useful to help us understand the issues at stake. In France, the building sector represents 44% of final energy consumption by sector, and 70% of consumption in buildings is dedicated to heating – by far the greater part in residential buildings. The average consumption of residential stock is high, around 274 kWh/(m².year); by comparison, the consumption ceiling set by RT2012 for new dwellings is 50 kWh/(m².year) in temperate and low altitude regions. This ceiling is expressed in primary energy and not in final energy. Final energy is the amount of energy available to the consumer. Primary energy consumption is that required for the production of this final energy. Per energy accounting conventions, as a result of losses due to production, processing, transportation and storage, 1 kWh of final energy = 2.58 kWh primary energy for electricity and 1 kWh of final energy = 1 kWh of primary energy for other forms of energy: such as gas, heating networks, wood, etc.

The amount of individual houses, which are structurally less efficient energetically than collective housing complexes, is not the only reason for the poor performance of the building stock. The Parisian residential stock is just as energy intensive as the national average, with 45% of stock (2.1 of 5.3 million units) in the three lowest energy classes (E, F and G). But individual houses only account for 27% of the stock as compared to 56% for metropolitan France as a whole. Moreover, the average size of a Parisian housing unit is significantly smaller than the national average. The poor energy performance of the Parisian housing stock is mainly due to a significantly lower turnover rate in new construction in comparison with the national average and to the low rate of building renovation. In addition to these two factors, the Île-de-France region accounts for almost 40% of public buildings built in France between 1950 and 1980. The construction methods most frequently used during this time (frame and facades in reinforced concrete, large glazed surfaces and simple glazing) are particularly energy intensive.

A potential for considerable savings

Given the state of the building stock in Europe and the power of the technologies available today, the insulation at the French RT 2012 level of a typical, not particularly energy intensive, residential building allows heating costs to be reduced by a factor of 10. Using the previous version of the regulation, which dates from 2005, already permits a reduction by a factor of 3. If the requirements of RT 2005 were applied at European level, the savings would reach 500 million oil equivalent tons (41.868 GJ or 11,630 kWh): the magnitude of the primary energy consumption of France and Germany combined!

Is it so difficult to achieve these savings? The best way to assess this issue is to take as an example a house built in Nancy in the 1960s with an energy class rating of F. This corresponds to 30% of the French housing stock. With a recent oil-fired boiler, the average heating bill reaches 3300€ per year. In the residential sector, the most profitable and powerful short-term intervention is to improve the performance of the building shell, and this house is no exception. As a first step, with a simple work plan requiring approximately 10,000€ (loft insulation, thermal exterior insulation, double glazing, single flow VMC), energy efficiency can be improved to a class C rating and the heating bill halved. The investment pays for itself in seven years’ time without even taking into account the valuation of the property. If the improvements are undertaken at the same time as other work, such as restoration or programmed expansion, profitability is further increased. With the availability of variable interest loans, such improvements can result in immediate cash savings for the owner.

It is because of this potential for considerable savings and the high socio-economic profitability that most developed countries have raised the energy efficiency requirements in their building codes in recent years. This also explains the emphasis placed by most European states on building insulation in energy transition legislation, which generally lays out three priorities: working on the stock of existing buildings, as well as on the standards for new construction; encouraging or regulating insulation work at key moments in the life of assets, as in the case of scheduled repairs of roofing or façade renovation; and promoting the provision of specific credits for energy efficiency work. These represent concrete steps in a global context in which the building industry is supposed to reduce its CO2 emissions to 84 gigatonnes by 2050  (target set by the World Green Building Council, an association of actors in the building value chain that was established to promote sustainable construction) to keep global warming below 2°C.

Francois Michel
Chairman, Ecophon (Saint-Gobain Group)