Hempcrete was placed at the heart of major restoration work on an iconic chateau in Luxembourg. This bio-based material has proved its worth as an ideal solution to meet all the requirements for renovating a historic building.
Construction of one of the most important chateau of the Grand Duchy of Luxembourg.
Renovation and insulation of the chateau with Tradical® Hempcrete
In the period intervening these two dates, the Grand-Château d’Ansembourg left lasting impressions, with its extensions, its economic role, its ever-flourishing gardens and park, its different owners and its important place in Luxembourg’s heritage.
Surrounded by world-famous, picturesque botanical gardens, where the delicate and fragrant Jardins d’Ansembourg rose was recently unveiled, the Château d’Ansembourg is experiencing a rebirth thanks to the expert advice of the Service des Sites et Monuments Nationaux or SSMN (Luxembourg’s department for national heritage).
The renovation work made it crystal clear that using a natural, bio-based material, such as Tradical® Hempcrete, is the right and best solution for (insulating and) renovating historic buildings.
The work was also a perfect example of artisan builders working intelligently and communicatively together to organise and complete a large-scale project.
A whole range of tough constraints shaped this renovation and led to specific technical choices and ingenious solutions.
From quick renovation to large-scale project
To begin with, the project owner wanted a simple renovation of the first floor. However, preliminary surveys and inspections revealed that there were significant structural problems requiring a more general overhaul: cracks, sagging floors and stairs, etc.
A further issue – dry rot
Dry rot was identified in just a few places at first, but unfortunately, it soon became clear that it was more widespread (affecting 700 m²). The initial renovation project had to be completely revised to incorporate an approach closer to archaeology than renovation.
The renovation suddenly went from work on a just few dozen square metres to having to perform work on all the floors of the central building. Work was therefore undertaken on the structure and to treat the dry rot.
Finding the right solution
Now a large-scale project, the renovation of this part of the building brought several building specialists together to find a solution to meet all the constraints involved:
- Ensuring that the layout and ornamental features of the interiors were kept – sculptures, beading, overhangs, intersecting ribs, etc.
- Preventing the return of dry rot by creating the conditions for maintaining constant temperatures and moisture levels.
- Ensuring walls can breathe to guarantee longevity.
- Providing high-performance insulation.
- Recreating the natural historic look and feel (while also integrating any necessary modern elements).
An on-site and decisive test
In 2016, the hempcrete underwent a full-scale test on site in the annex off the Salon Bleu (blue room) on the first floor, a room measuring about 4 by 4 metres.
44 m² of surface area were lined with hempcrete cast on an embedded metal framework. The results confirmed the vapour permeability and acoustic performance of this bio-based material, and proved that this insulating lining could be used without compromising the architecture and the different decorative or ornamental elements.
Hempcrete insulation – a compelling approach
The idea of using hempcrete was quickly adopted, as the material provided:
- The right humidity control characteristics to enable the façade to breathe.
- Consistent material characteristics to prevent dry rot from reappearing. Dry rot comes from the stonework and spreads if certain humidity and temperature conditions come together. The fact that hempcrete provides a constant surface temperature for interior walls avoids such conditions arising.
- An indoor temperature of 20°C, as requested by the project owner.
Restoration choices governed by architecture and heritage
An inverted metal framework
With cellulose-hungry dry rot in mind, metal had to be used for the secondary framework. Profiles were positioned vertically at 40 cm intervals and a few centimetres away from the substrate.
For a perfect infill and an even coating of profiles, and to meet, for example, the specific thickness required for the correct distance between the flat surface featuring the decorative friezes of the vaults and the flat surface of finished insulated walls (recommended by the SSMN), Weber Tradical®’s Technical Manager, Yannic Santandreu, proposed the ingenious solution of using U-shaped profiles.
Tracks (48 mm) were positioned with the concave part of the profile facing outwards. This solution ensured that the profiles were coated with a sufficient thickness of hempcrete to support the expansion and contraction effects inherent to all materials, and avoid any deterioration through fissuring.
The hempcrete was made in a concrete mixer and poured into the gap between the OSB shuttering panels and the walls, in compliance with the French professional rules for hempcrete. Thanks to this innovative solution, the framework was firmly coated with a thickness of between 7 and 10 cm.
Reversible insulation work – a must for renovating historic buildings
One of the main concerns of the project owner and the SSMN was that the work undertaken should not damage the original building. The insulation had to be removable should the need arise in the future. Hempcrete supported by a metal framework that is separate from the substrate can be easily removed if necessary.
Maintaining breathability with air lime finishes
An air lime finish was applied to the hempcrete as a thin coat of render – Tradical® Décor – whose vapour permeability is in perfect harmony with the moisture transfers inherent to this bio-based insulation. The thin lime render was also used on the mineral-based wall substrates adjacent to the insulated walls. The advantage of this render is that any work delivered is texturally and visually harmonious, regardless of the type of substrate to be finished.
A constructive meeting of artisan builders – or the small business’s guide to completing large-scale projects
Atelier Saint-Fiacre France (stone cutter), Entreprise Hennen, Société Millereaux and Atelier Montomble, all won over by hempcrete and trained by Weber in the use of Tradical® Hempcrete, took a methodical approach. They pooled their efforts, shared their experiences and knowledge, tightly scheduled the different work stages and optimised costs. A work and primary material delivery schedule was set out over period of about ten months, at a rate of one week of work per month.
Project profile for the restoration of a historic building
- Work site: Grand-Château d’Ansembourg
- Location: Ansembourg, Grand-Duchy of Luxembourg
- Purpose of the building: Tourism, seminars
- Characteristics of the building: Historic building (dating from 1640)
- Project owner: Private project owner
- Main contractor: Agence N. Madoki
- Restoration supervised by: Service des Sites et Monuments Nationaux
- Builders & artisans using hempcrete: Atelier Saint-Fiacre France (stone cutter) / Entreprise Hennen / Société Millereaux / Atelier Montomble
- Expected delivery: 2019
- Surface area concerned: 1,500 m²
- Product volume: 130 m3 of hempcrete
- Tradical® Hempcrete bio-based insulation: Tradical®PF 70 lime + Chanvribat® hurds
- Thin air lime-based interior finishing render: Tradical®Décor
Tradical® Hempcrete quality hallmarks:
- Certified aggregate
- Made in France
- Compliant with French Professional Rules
For further information:
- Contact : firstname.lastname@example.org
Note 1: extract from the press kit produced by Sandrine Wiart, Weber press officer, in June 2018. Document title: AT THE HEART OF MAJOR RESTORATION WORK ON AN ICONIC CHATEAU IN LUXEMBOURG: HEMPCRETE. The kit was finalised after a press visit to the site on 27 June 2018.
Note 2: Photo credits – ©Weber Tradical®