MACH - House Comforted by Humidification

In a global context of disruption and climate change, natural phenomena are multiplying in a recurring manner with greater intensity. The year 2020 is an extraordinary year: the hottest in France since 1900 [ 1 ]. The 2020 temperature in France, consolidated with the forecasts for December 28, is 14 ° C, thus exceeding that recorded in 2018 (13.94 ° C). Thus, in 2020, we experienced the warmest winter since the beginning of the 20th century [ 2 ], the driest summer (from June 21 to September 20) since at least 1959 [ 3 ] and an exceptional episode of heat in September [ 4 ]. Even more recently, we experienced the hottest November 2020 on record worldwide [ 5 ].

In 2019, drought was ranked 1st natural risk in terms of costs of damage caused, estimated between € 600 and 870 million by the Caisse Centrale de Réassurance (CCR), and a third of the French territory affected [ 6 ]. The current trend is not likely to be reversed in the future in the context of climate change, with 6,265 applications for recognition in a state of natural disaster (Cat-Nat) drought 2019 processed, of which 47% are favorable and 2.1 million houses in the medium-strong RGA zone [ 7 ]. In the long term, projections illustrate this trend through an increase in the cumulative cost of drought insurance by + 162% over the period from 2014 to 2039 [ 8 ].

Cerema, awarded the Carnot Institute "Clim'adapt" label in 2020, is stepping up its efforts in favor of adaptation to climate change through applied research and innovation .

From the end of 2016 to the end of 2020, Cerema experimented with a new remediation solution, MACH, based on the re-humidification of clay soils during the drought period by making use of rainwater, previously collected and stored (during the wet period preceding the period of drought). drought). The principle of the MACH solution aims to maintain a balanced water state at the level of the foundation soil, despite the phenomenon of shrinkage and aggravation under the effect of evapotranspiration and vegetation, in order to stabilize the opening of existing cracks. in the structure and prevent the initiation of new cracks. The results, recorded during the last 4 years of intense droughts, are encouraging in terms of stabilizing the opening of existing cracks instrumented by crackometers.

Sustainable development approach of the project owner

The house was built on very plastic clay soils, subject to the phenomenon of RGA (shrinkage swelling of clay soils), with shallow foundations. With the effects of climate change and the increasingly intense droughts since the summer of 2015, structural damage has appeared inside and outside the house.

In fact, the differential settlements of the foundation soil due to the phenomenon of shrinkage during the drought period, then the swelling undergone during the wet period in a cyclical manner under the effects of climatic disturbance affect the mechanical properties of the soils and can induce instabilities at the level of the structure.

The objective of the MACH solution is to maintain a balanced water state during the drought period to limit the phenomenon of subgrade shrinkage and thus stabilize existing damage and prevent the appearance of new damage.

The advantages of the MACH solution are numerous, the main ones being:

• ecological : the only resource for the operation of the MACH solution is the recovery of rainwater previously collected and stored,
• economical : compared to the conventional solutions available, the cost of which is at least 50 to 70 k € HT, the cost of the MACH solution at around 15 k € HT makes it accessible to all disaster victims,
• light installation: the installation of the MACH solution does not require the moving or rehousing of the occupants,

To summarize, our innovative approach makes it possible to provide a new effective concrete response to the growing problem of RGA while being ecological and economical.

Architectural description

The reinforcement work provided by the MACH solution vis-à-vis the natural phenomenon of RGA does not concern the architecture of the building but the stability of its structure.