In Nanterre, the mosaics of the famous Aillaud towers, also nicknamed the Cloud towers, enjoy their last hours shimmering under the rays of the sun. By 2030, at least eleven of them will be covered with a stainless steel skin to guarantee better thermal insulation. All this without forcing the inhabitants of some 1,170 social housing units to move temporarily. These buildings designed by Émile Aillaud, built between 1973 and 1980 and labeled “20th century heritage”, symbolize both for heritage protection associations, an art, a city and a piece of architectural history. . Also, the use of stainless steel decided by the city of Nanterre, which will profoundly change its appearance, makes them shudder.
A controversy that portends many conflicts to come. Because the acceleration of energy renovation work, as the fateful rental restriction dates approach, intensifies the pressure to renovate and insulate properties. From January 1, 2023, most buildings classified G according to the energy performance diagnosis (DPE) can no longer be rented under the climate and resilience law. The National Observatory for Energy Renovation (ONRE), estimates the total number of private housing units labeled F or G at 7.2 million, and therefore considered as thermal sieves. As much, therefore, to renovate quickly. Among them, a significant part can legitimately be considered as an integral part of the heritage. At a minimum, the buildings built before 1948, most of which have architectural qualities that are very different from what is done today. They represent 33% of housing in the French stock according to INSEE.
PVC, a new aesthetic standard
However, the renovation of the building at a forced march worries some specialists. “The houses could become like these white PVC wind turbines which are the same from one region to another,” warns Julien Lacaze, president of the Sites & Monuments heritage preservation association. In its viewfinder, the renovation works which concentrate around small changes of individual elements such as windows or doors and for which the use of PVC is generalized. Recognized for their quality of thermal and sound insulation, the proliferation of these materials de facto makes disappear a whole section of the architectural heritage which prevailed until then. “We have already lost most of the old carpentry, especially with the disappearance of the old windows. There were marvels: wrought iron espagnolettes, blown glass tiles… It’s a whole regional diversity that is disappearing “, blows Julien Lacaze, a mixture of anger and resignation in his voice. However, solutions exist such as the double-window system or the installation of double glazing which would allow the original exterior appearance to be preserved. But these methods are often more expensive and the effectiveness is not necessarily there.
The president of the association is also worried about the introduction of materials with a shorter lifespan in buildings designed to last several centuries. PVC or polyurethane, derived from petroleum and guaranteed for only ten years, are gradually replacing “local materials which have shown that they can withstand time”. The gains in CO2 emissions made possible by the insulation could thus be weakened by those emitted during the manufacture of materials, far from being eco-designed and having to be renewed on a frequent basis.
The fear of insulation from the outside
Another, greater danger could threaten French landscapes… The insulation of houses from the outside. When securing the slabs, whether hemp or polyurethane, the architectural details are concealed. Thus, the moldings of the facades, the ornaments or the bricks are masked in favor of a uniform paint, usually white, or a wooden cladding. According to their opponents, these practices contribute to the standardization of landscapes.
In the viewfinder of some experts, business conglomerates like EnergieSprong. The Dutch program, in force in seven countries, already provided for 6,000 projects in France at the end of 2021. The latter advocates on its website “off-site renovation solutions” which would be “identical from operation to operation” comparable to “”ready-to-wear” solutions. An approach that adapts perfectly to large housing estates or housing estates of the glorious Thirty, but works much less for old residences or modern architectural works. “They grasped the problem deadlines and arrive with a heavy rehabilitation product which responds, on paper, to current issues but whose carbon footprint is not negligible (due to the materials used, editor’s note)”, points out Marie-Jeanne Jouveau, heritage architect .
For her, “multidisciplinary diagnoses are needed to adapt to heritage constraints”, at least an architect and a diagnostician, to not be satisfied with a purely quantified energy vision. A few weeks ago, the architect wrote an open letter to this effect, co-signed with Dorian Bianco, a doctoral student in the history of architecture. The latter fears that the haste caused by the entry into force of the legal texts will encourage the choice of industrial solutions with disastrous results. If, according to him, the debate “is not yet public”, in particular because the consequences are not yet visible, it is only “a matter of time” before complaints multiply. Because beyond the aesthetic and heritage issues, there is also the question of technical efficiency which would require personalized assessments according to the construction materials, the orientation of the house or its use.
Choosing “tailor-made” versus “ready-to-wear”
With regard to insulation, one solution could be to favor interior work, which is more discreet. However, the constraints of the approach are heavy: relocation of the inhabitants, loss of energy at floor level or poor temperature regulation in summer. So many reasons put forward by the town hall of Nanterre to cover the eleven Aillaud towers with stainless steel…
And the examples of this puzzle to come are not limited to these large Ile-de-France towers: the stone houses, which would risk falling apart, the adobe houses of Auvergne or the very low houses of the 17th century cannot be isolated from the inside without seeing the living space ostensibly reduced. In these cases, and many others, the energy renovation will go less through full insulation than through other less heavy renovation gestures. The mode of heating, the mixture between lime and hemp, invisible to the naked eye, or even the insulation of specific parts of the dwelling, could be considered. Practices that require an in-depth analysis of the situation. Except that one problem persists: made-to-measure will always remain more expensive than ready-to-wear… In the context of the inflationary pressure of materials and the lack of a workforce sufficiently trained in renovation, low-cost services risk seeing their power of attraction reinforced.