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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
Interested in learning more about Tradical?

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finition chaux aérienne en rénovation intérieure
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Hempcrete – a perfect match

When you renovate, it is particularly important to use insulating materials that work in harmony with the materials used in the original building and that can match the longevity of old buildings. AC Déco uses all the potential of Tradical® Hempcretes to deliver renovations based on quality and comfort.

We went on a guided visit of a site in the Charente-Maritime department.
BCB Tradical® interviewed Sébastien Tinchant from AC Déco on 25 October 2019.


BCB: How did you meet your client?

Sébastien Tinchant: The building was bought by some English people who wanted to live in an eco-friendly house. They were already interested in this type of approach because of their professional work. They knew about lime and wanted to use local companies. That’s how they discovered my business and my green building experience.

I did what I always do and showed them and the main contractor round my previous work sites. That enabled me to explain the potential of hempcrete properly, in terms of thermal performance and moisture transfer, and how this material and stone work perfectly together. The heating engineer noted the characteristics provided in the Tradical® brochure to adjust the heating power of the wood chip boiler to be installed. The aim was that the client would produce his own wood chips for the boiler.


BCB: What was the configuration of the house?

ST: It was a house in Charente-Maritime with a large footprint and comprising a ground floor and two upper floors. The first floor walls were made of rubble stone and on the second floor they were made of ashlar. There were several entrances to the house via four staircases. This was very important given that part of this house was to be rented out as a gîte. The future visitors were to have their own private entrance.


BCB: What did the works programme look like?

ST: As the house was to have two uses, it had to have several bathrooms (eight in all). The project owner wanted to use hempcrete for insulating the walls and the ground floor screed. The house was completely emptied, but the floors were kept on the upper floors along with all the beams.


BCB: How did you programme the different stages of the renovation work given the time required for hempcrete to dry?

ST: The main work stages were straightforward. We started by laying the hardcore layer and the hempcrete screed. The builder then stepped in before we sprayed the insulating lining.

The insulating screed

More specifically, the earthwork contractor laid the pozzolana hardcore layer over part of the ground floor area following my instructions. The other part of the ground floor area covered in cement floor tiles was left as it was to avoid unnecessary demolition work.

Several drains were installed to ensure the hardcore layer would be well ventilated, with a system that ran right up to the rooftop to create a natural flow of air from the bottom to the top of the building.

The 17 cm thick hempcrete screed was left to dry. Once dry, we tiled it with traditional Pauzat terracotta tiles.


While the screed was drying, we got on with other work at the site:

  • The roof was insulated.
  • The mason created new openings and stripped the internal walls.
  • The house was entirely rewired.
  • Conduits and pipes were installed at the same time, with piping for the cast iron radiators on the upper floors and for the underfloor heating on the ground floor.
  • Preparations were made for the insulating lining by installing a secondary framework, along with framework for the openings.


The indoor insulating lining

We sprayed an 8 cm thick layer of Tradical® Thermo plus Chanvribat® Hempcrete on ground floor walls and on the inside of external walls on the upper floors. The output for this type of work is 2 m3 per hour, i.e., 10 m3 per day. To make sure we had the right settings for everything to work properly, I added a flow meter at the start of the pipe which carried the milk of lime.

Hempcrete is cast from the bottom upwards. You wet the substrate using milk of lime and then spray a first layer of hempcrete to obtain a surface that’s uniform. You then spray another layer up to the pre-defined thickness. The final touches are made using a 1.4 m long serrated darby and with the help of the pre-installed guides.


BCB: When did you start work on the finishes?

ST: After a month of drying, part of the lining was ready to be coated with a traditional lime render – consisting of a base coat and a lime plus sand dubbing out coat (sprayed on using the same machine) – made with Tradical® Bâtir and local Cadeuil sand, whose colour ranges from ochre to red depending on where it was extracted. It’s a well-graded sand with a particle size of 0/3.

We then chose finishes depending on the look to be created in each room. In most rooms we applied a thin lime-based Tradical® Décor finishing render for a fine-grained, floated finish. In the hall, we finished the walls with a super-thin lime render, Tradical® Finilys, applied al fresco as a single coat (smooth finish) or in two coats (burnished finish).


Lime and hempcrete project profile

  • Project owner: Private individual
  • Location: Charente-Maritime
  • Builder: AC Déco, 16 rue du Bosquet, 17250 Sainte Radegonde, France ||


Lime and hempcrete technical solutions

1- Hempcrete insulation

  • Hempcrete insulating lining: Tradical®Thermo + Chanvribat® | Density = 280 kg/m3
  • Hempcrete insulating screed: Tradical®Thermo + Chanvribat® | Density = 325 kg/m3
  • Tradical®Thermo and Chanvribat® is an approved lime and hemp blend that complies with the performance requirements of French professional rules for the construction of hempcrete structures.
  • Chanvribat®is a Granulat Chanvre Bâtiment certified hemp product.


2 – Traditional lime preliminary render


3 – Lime finish

  • Tradical®Décor, a ready-to-mix thin air lime render for creating a thin finishing render. For this project it was applied on a perfectly smooth Tradical® Bâtir plus sand brown coat.


4 – Decorative finish

  • Tradical®Finilys: a super-thin ready-to-mix lime render applied as a single coat for a smooth finish
  • Tradical®Finilys: a super-thin ready-to-mix lime render applied in two coats for a burnished finish


Interested in learning more about Tradical?

BCB Tradical®:

More examples about hempcrete homes and buildings


This project was launched in early May 2017 in Montech (in the Tarn-et-Garonne department). The internal brick and stone walls of the building were stripped to remove the cement mortar covering. Our Tradical® Hempcrete insulating lining outdid itself as an easy-to-cast material, with a total wall surface area of 200 m² to cover for this project. The framework was installed in the morning and then shuttering was erected, infilled and removed in stages right up to the ceiling. Within only 24 hours, the first room was finished!


Restoring and insulating as a DIY builder

Interview with Mr Gilles Mollard, self-builder,
conducted in September by BCB


BCB: Can you describe the background to your renovation project?

GM: The idea was to renovate a traditional farm we had inherited. The farm is located in Montech, in the Tarn-et-Garonne department. There’s a large main farm building, with the same floor area of 100 m² on the ground floor and the first floor, which needed renovating. There’s also an 80 m² stable, which had already been renovated.

In terms of temperature, it gets very cold for about a week in winter with temperatures of between -7 to -10°C. Otherwise, average winter temperatures range between 1 to 5°C in the mornings, with warmer afternoons. In summer, the temperatures can rise up to 38°C. The range of summer and winter temperatures means we need high-performance insulation all year round.

The relatively poor state of the building made us decide to renovate it. The 30 to 40 cm thick rubble stone walls were in a bad state due to a high level of damp. The reason for this was that the building had been formerly renovated by coating the internal walls with a cement render. This didn’t prove to be ideal and it was then covered by a brick veneer. A smell of dampness permeated this family home. Living in it was impossible for us and we wondered how to improve the situation.

BCB: How did you discover hempcrete?

GM: A materials supplier, Point P, suggested the hemp-lime solution when we told him about the state of the building and our project. I then browsed the web for more information.

We wanted simple solutions that would suit our walls and insulate them. I really didn’t want to go for the conventional storey-high panel option, as our walls were neither straight nor flat. I looked at the different solutions with the idea that the walls should be able to breathe.


BCB: A two-stage renovation project

GM: The first thing we did was to let our walls breathe again by stripping them and coming back to how they were before the previous renovation work. We took the brick veneer and the cement off to reveal the underlying rubble stone. The second thing we did was to properly restore and insulate the walls.


BCB: Why did you choose to use hempcrete as an insulating lining?

GM: I wanted to apply insulation directly onto the walls to repair and insulate them at the same time. I quickly realised that we needed to avoid creating thermal bridges if we wanted the insulation to be really effective. So, we reconsidered how we were going to do the floors, for example, so that we could insulate continuously from ground floor to roof, without there being a gap where the ground floor walls met the first floor.


BCB: What made you decide to do all this work yourself?

GM: I didn’t know anything about using the materials we chose. And I’m not a professional builder. It was all completely new to me. What really made me decide to do it myself was the excellent support I received from your technical consultant.


BCB; What were the key points to remember for successfully completing the work?

GM: One of the important things was to create a layout plan for all the electrical conduits so that the sockets would be in the right places on the battens.

These battens, which were part of the insulating lining solution, form a light frame structure fastened to the walls and are very easy to install. There’s no hard and fast rule about them being properly aligned or straight. This is such an advantage when your substrate is old walls!

What I did spend time on was laser positioning the screw heads on the battens. The heads determine the flatness of the surface of the cast hempcrete. They act as spacers for placing shuttering panels at the right distance and also as guides for installing the power sockets.


BCB: Can you give us an idea of the timing for the work?

GM: All the preparation work was key to making it easier to cast the hempcrete insulating lining. I was really surprised at how easy it was to install the shuttering, fill the gap between the wall and the panels and then remove the shuttering. It only took half an hour for a whole length of shuttering panels! And the end result looked very good.

BCB: What was your time schedule for actually doing the work?

GM: The work started in May 2017 and we finished the ground floor in early July 2017. We only worked weekends when we were free.

If I add all the time spent working on the project, it comes out at about 12 days, working from 9 am until 4 pm, to complete the hempcrete insulating lining on the ground floor.


BCB: What’s your initial verdict on having chosen this ‘insulating lining’ solution?

Using a wet mix (hemp+lime+water) instead of dry solutions (fibres or wools) was not an issue. Hempcrete had the added benefit of enabling me to fill in defects in the walls at the same time as insulating them thanks to the thickness cast.


‘For me, hempcrete is masonry work that insulates too.’

When all is said and done, casting hempcrete is much faster than installing ceiling-high panels, for example, which requires accurately setting up a framework, installing the insulation, preparing the panels (joints, sanding, primer) and applying the finish. And in the end, is that kind of system really that breathable and durable?

As for Tradical® Hempcrete insulating lining, it’s easy to set up the framework, and the shuttering and infill system are fast to implement. And when it’s dry, you can apply a lime finish on it directly.

‘I’m also reassured by this material’s resistance to rodents, which is really important when you live in the countryside.’

BCB: Do you have any before-and-after impressions to share with us?

GM: Not for the moment as the work is very recent, but I can already see the benefits for the house. The pleasant smell of hempcrete is a welcome change from the damp smell we had before doing work on the house!

We’re not living in the house full time yet as there’s still work to be done. But when it’s cold and we go there, we’ve noticed that the atmosphere is more pleasant. There’s not that ‘cold wall effect’ feeling any more.


‘With just 10 cm of Tradical® Hempcrete, we achieved our objectives! In terms of acoustic performance for one of the bedrooms too, where all the walls are lined with hempcrete.

It’s an exceptional product.’


BCB: What finish are you planning to apply to the hempcrete?

GM: Hempcrete lining has a beautiful natural look and it seems a shame to cover it at all. But I think I’m going to cover it with a Tradical® Décor lime render after all, to protect it. It can be applied as a very thin coat, the texture is very easy to adjust and it complements the lining nicely. What more can a non-professional like me ask for?

Before applying the finish, we will have given the hempcrete plenty of time to dry as work on the house progresses.


What conclusions can you draw from your experience of using this unrivalled bio-based material?

GM: Overall, hempcrete is simple to use and apply. The spirit of our house has been left intact. The insulation offered by the material has already provided a feeling of comfort and the design freedom it also offers has given our house its old charm back.


‘Today, I feel relaxed. Now that the lime and hemp lining has been cast, I just have to finish the renders. The work we’ve done will last for years. What more could we want!



Montech project profile


  • Tradical® Hempcrete: Tradical® Thermo lime and Chanvribat®
    Thickness: 10 cm on average
  • Lime finishing render: Tradical®Décor

Environmental footprint
20 m3 of Tradical® Hempcrete = 5.7T of CO2 stored


Interested in learning more about Tradical®?

BCB Tradical®:

More examples of hempcrete homes