In the Parisian suburbs, a city that builds with straw

In the Marnaudes district of Rosny-sous-Bois (Seine-Saint-Denis), this project aims to make “the city more resilient in the face of climate change” while comfortably welcoming more and more students, explains to the AFP Charlotte Picard, the city architect who is monitoring the construction site.

Already five public buildings, three schools and two leisure centers have been built in this city according to eco-construction precepts using biosourced and local materials, encouraged by the UN, to replace concrete and steel, and fight against global warming.

Insulation and even straw construction were developed in the United States at the end of the 19th century, especially in Nebraska, with the first straw balers. In France, the first wooden frame house insulated with straw, built in 1920, still stands in Montargis (Loiret).

In Ile-de-France, a cereal-producing region, wheat straw is a "local, abundant and inexpensive" product, argues Edouard Vermes, craftsman, during training in earth-straw construction that he runs in Romainville ( Seine-Saint-Denis) for around fifteen interns, mainly architects.

“10.000 buildings”

“It’s better than polystyrene cladding from the other side of the world, or glass or rock wool”, whose production system is not very green, adds Christophe Benoit, also a trainer on the same course. .

Their trainees learn to coat themselves a wall of straw bales embedded in a wooden frame, with three layers of moistened clay soil.

Since 2012, France has been one of the rare countries in the world to have recognized professional rules and insurance allowing straw construction, thanks to the work of the French Straw Construction Network bringing together craftsmen, builders, architects and engineers, all passionate.

Today, “some 10.000 buildings are insulated with straw” in France, explains Christophe Benoit.

You can find everything: public buildings like in Rosny or individual housing. In the heart of Paris, a student residence was built with a wooden frame and straw insulation, and seven-story social housing was renovated with straw insulation on one of the gables in the 15th arrondissement.

“It hardly burns”

In addition to storing CO2, the straw material ensures thermal comfort in summer and winter, for example by retaining the penetration of heat for a very long time, ideal for heatwave days, admits the CSTB (Scientific Technical Building Center) which has validated the process.

Provided that the wheat is well dried during storage, that the straw is laid following the instructions on the wooden frames, preferably not on a rainy day, and that the earth coatings are applied according to the rules of the art .

Fingers reddened by the clayey earth that she has just spread to form the second of the three layers of earth necessary for a successful coating, Noémie Roux, architect of the Lieu Fauve agency, based in Paris, Lyon and Mayotte, evacuates from 'a laugh at the myths conveyed in children's stories about straw houses that are on fire, blown away or flooded.

“The straw is very compressed, there is little oxygen in it, in fact it burns, but it hardly burns since the fire is not fed,” she notes.

A difference compared to certain cheap plastic facade insulation, from the other side of the world and accused of being responsible for the rapid spread of facade fires, as in the case of Grenfell Tower in London in 2017.

To ensure waterproofing, “you need a large roof overhang and above all a coating which protects against humidity”, underlines Noémie Roux. And against the wind, we apply stiffeners to the wooden structure so that the building holds up.