Project Details
Date: 2016
Location: Ardèche department (07)
Maitre d’ouvrage: Private
Entreprise: JM Alliez
Category: eco-renovation-houses

Project Description

To present this showcase project, BCB interviewed Jean-Marie Alliez, who had an important role to play and is a Tradical® Hempcrete specialist, using hempcrete in many of his projects.

On this project, a contemporary design completely transformed the original space. The large volumes made it easy to totally redesign the different areas for living and circulating. The variety of perspectives, the materials and textures used, and the aesthetic attention paid to conduit and duct features are a pleasure to behold.

And it’s all reversible.

The success of the project also came from using materials with thermal and moisture-regulating properties that work in perfect harmony with the existing building. We all know thermal comfort that one-metre-thick walls can bring! Here, it was just a question of adding to the existing potential.

BCB: Can you tell us the story behind this renovated building?

JMA: The work site, located in a village in the Ardèche, consisted of a large second floor room with a church-like barrel vault. The room was 20 m long by 8 m wide and 8 m high. The place had been used as a dormitory until 1950 before being abandoned and falling into disrepair.

The vault was in poor condition, but you could still see traces of the light blue paint or wash with a burgundy border on the lower edges. A large crack ran along the apex from one end of the room to the other. Before I took on the project, the roof above the vault had already been completely rebuilt and tie rods had been installed to consolidate the vault. A previously installed chimney flue made of clay flue liners ran up the centre of the room; it had been used to evacuate the smoke from a ground floor fire place.

My client owned all the buildings around this room.

BCB: What were the main phases of work for this site and which building trades were involved?

JMA: The building work had six main phases:

Phase 1: Remy Larmande (builder from the Ardèche department)

The entrance to the apartment was changed by creating a new opening leading in from the stairwell in the neighbouring building and by building a landing and staircase.

  • The chimney flue was clad with concrete.
  • The former entrance was blocked off to allow for the current kitchen area.
  • The indoor circulation areas were modified by adding a mezzanine and a gangway.
  • The timber-framed windows were replaced and topped with fixed semi-circular fan-style windows.
  • The pre-wired electrical conduits and water pipes were installed.

Phase 2: JMA-Bâtiment Conseil and Art Pierre Tradition (Sylvain Delisle)

  • All the surfaces were sanded (walls, vaulted ceiling) and the dust was cleaned off.
  • A 10 cm thick layer of hempcrete insulation was cast using
  • a Euromair spraying machine (two days).
  • The hempcrete was left to dry for six weeks.
  • A 17 cm thick lime and hemp screed was cast for the kitchen area.
  • A compression screed made of Tradical PF 55 and sand was cast.

PHASE 3: Remy Larmande

  • The kitchen and bathroom were built.
  • The south-side access was blocked off (to separate the apartment from the adjoining house).
  • Finishing work was carried out (staircase, iron work, floors, installing electrical boxes).

PHASE 4: JMA-Bâtiment Conseil and Art Pierre Tradition (Sylvain Delisle)

  • A Tradical® PF 80M Hemp Render was applied over a surface area of 230 m2, with an average thickness of 3 cm on all walls and up to a height of 4.5 m. It was applied on Tradical® Hempcrete and non-insulated walls.
  • A Tradical® Décor decorative finish (and orange marble powder) was applied to the vaulted ceiling (200 m2) – the first coat included a mesh on the cracked or damaged areas, which had been repaired beforehand.

PHASE 5: Remy Larmande

  • Wiring terminals were fitted.
  • Finishing touches were added to the iron work.
  • The kitchen was installed.
  • The built-in shelving was put up, the tiling was laid and the staircase, cupboard and joinery elements (doors) were installed.

PHASE 6: JMA-Bâtiment Conseil and Sandrine Gourju

  • Finishes were applied to the ironwork and steel cables were installed for the handrails.
  • Finishes were applied to OSB panels (microporous clear varnish) and to the concrete floor.
BCB: Why was the hemp and lime composite material chosen for insulating the walls?

JMA: The idea was to insulate (without thermal bridges) the external walls up to a certain height (5 m at most) to be able to keep the vaulted ceiling. The hemp solution meant the insulation thickness could be adapted and tapered off at the base of the vaulted ceiling. By using machine projection, we were able to leave the mix in the trucks below, just outside the building (the room was accessed via a narrow staircase in an adjoining house). With ‘conventional’ insulation, all the equipment would have had to be brought up. The project owner contacted me as he wanted a healthy solution. The first solution that came to mind, of course, was hempcrete combined with a hemp and lime render. This solution also enabled us to have the same colour everywhere, on the hempcrete and on the non-insulated walls. The colour of Tradical® PF 80M Hemp Render suited my client, although I also offered either a limewash or Tradical® Décor finish to change the colour and aspect.

BCB: Why have one material for the walls and another for the vaulted ceiling?

JMA: We decided that insulating the vault (with a hemp and lime solution) was ‘unnecessary’ in view of the height of the ceiling and the vault’s thickness – above the vault (under the roof) there’s a thick layer of rubble acting as a loading force. The owner wanted to the room to be a light as possible and was quick to agree to the idea of a white-coloured vault.

The substrates were prepared and any cracks and damaged areas were repaired (filled and meshed) at the same time. If we had applied a coating of something like limewash on this heterogeneous substrate, the end result would not have been very harmonious. So, I suggested finishing the vaulted ceiling with Tradical® Décor applied with a sponge effect. To avoid any unsightly joins, the entire 200 m2 surface area was completed in one go in a single day by three people working with mobile scaffold towers.

BCB: How did you solve the issue of joining these two materials that have such differing thicknesses, textures and colours?

JMA: The Tradical Hemp Render was applied to the walls first. The thickness applied was gradually tapered off between the heights of 4 m and 4.5 m up from the floor. The render was floated and smoothed right up to the top to make it easier to cover the join between this material and the vault.

Before applying the Tradical® Décor finish, the hemp render had to be protected from splashes to avoid stains. Timber battens were fixed all around the walls using a rotating laser level set to the required height (about 4.3 m up from the floor). A plastic sheet was then stapled to the battens and hung down to the floor. The battens acted as dividers between the wall and the vaulted ceiling.

BCB: What were the existing substrates, materials and finishes like?

JMA: The existing substrate was the original lime and sand render (18-19th century) coated with a limewash. Some parts had been repaired with plaster. At a later time, the base of the walls had been coated with lead paint. When we were preparing the substrates, I sanded the surfaces entirely.

BCB: In old buildings, you always check for any existing problems. Were there any in this apartment and in the building in general?

JMA: Yes, we repaired several damaged areas, such as where water had infiltrated due to old leaks in the roof and where the height of the window openings had formerly been reduced, causing cracks where the wall met the vault. The vault itself had a crack running along its entire length.

However, the apartment being on the second floor was a real advantage as we didn’t have any of the issues of rising damp that frequently occur in stone walls. So, there was no saltpetre.

The only part of this building that sometimes suffers from damp is the basement. That meant we had a building in good overall health.

BCB: How did you approach the issues of thermal comfort and moisture regulation with regard to the existing structure which consists of very thick walls? Did you have an idea of the existing thermal comfort in summer?

JMA: I talked to my client about how regulating the level of humidity indoors helps to provide thermal comfort. Hempcrete is perfect for regulating humidity.

We didn’t have access to any information on prior energy consumption for the building, so we can’t really make a comparison. What I can say though, is that for the whole duration of the works, through winter and summer, the indoor temperatures remained very pleasant. In summer, during the hottest part of the day, the sun doesn’t heat the apartment and in winter, when the weather is at its coldest, the indoor temperature remains comfortable without having to turn the heating on. The high thermal inertia of the walls was respected by using self-insulating hempcrete applied to the inside of external walls.

In terms of noise, there was a lot of echo before work started, but once the hempcrete had been cast on the walls, the acoustics became very pleasant. There was no more echo and the coat of Tradical® Décor applied to the vault improved the acoustics even more by providing a clearer sound (prevents reverberation).

BCB: What heating method was installed and what was the aim for energy consumption?

JMA: A modern electronically-controlled pellet stove was installed. One pallet of bags of pellets was ordered before the end of the renovation work. The lime-hemp renders finished drying with the help of this heating system and by airing the place daily.

BCB: How is domestic hot water produced?

JMA: The hot water for domestic use is heated using an electric water heater. As the apartment can be rented out and therefore used by people for short periods of time, we opted for straightforward solutions for domestic hot water, heating and so on, to make it easier in terms of servicing and maintenance.

Thank you, Jean-Marie, and we look forward to hearing about your next project!


A few figures
  • Overall R value after renovation
  • Existing R value 0.7 + R value for insulating lining 0.18 + hemp render 0.17 = 2.05 m².K/W
  • Carbon capture
    6 m3of Tradical® Hempcrete and Hemp Render, generating 9 T of stored CO2
Project profil
  • Project owner: Private individual
  • Living space: 155 m²
  • Builders specialising in hempcrete and hemp render: JMA Bâtiment Conseil
  • General builders: Remy Larmande
  • Hempcrete: Tradical® PF 70 + Chanvribat®
  • Surface area: 230 m²
  • Hemp render: Tradical® PF 80 M + Chanvribat®
  • Surface area: 230 m²
  • Finishing render (vault): Tradical® Décor
  • Surface area: 200 m²
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