Marcel Deravet (IFSB), Pierre Raulier (ULG)


Time-lapse of the construction

Pilot Id

FRESH is the Luxembourgish pilot project that will be installed on the roof of the existing restaurant extension of the Institut de Formation Sectoriel du Bâtiment (IFSB).

The IFSB is a training centre for the construction sector, notably sustainable construction, machinery, management, occupational safety and health, the environment. The institute's stated objective is to position itself as the expert centre for sustainable construction in Luxembourg and neighbouring countries (France, Germany, Belgium).

The IFSB develops services to meet and anticipate the needs of construction companies in Luxembourg. Its goal also includes being a Grand Ducal showcase for the construction sector and promotion of innovative projects. Urban farming is part of the future of construction. Therefore, the IFSB and the Conseil pour le Développement Economique de la Construction (CDEC) participated in the drafting of the national strategy presented by the government of Luxembourg.

Luxembourg is a country where real estate develops very fast but cannot meet the needs related to demographic pressure. In this context, the IFSB saw an opportunity to develop a tool for the construction sector. The objective is to anticipate the needs of cities in the future, particularly in relation to food needs. This is where RTGs enter the scene.

The greenhouse will cover around 370 m² on top of the IFSB restaurant. It will be located near the training site, and the plants grown in it will be in part served directly in the restaurant below. The project objective is to integrate a food production greenhouse on top of a restaurant. Raising people's awareness of what they eat will involve reconnecting them with food production. Popular and appreciated products such as tomatoes will be prioritised to meet the needs of the restaurant. 

To strengthen the link between vegetable production and vegetable use in restaurants, a corridor around the greenhouse will allow visitors to view the production area without disturbing operational activities.

Finally, the connection to the building for CO² and heat recovery will make sense for the building sector. CO² recovery is an upcoming challenge for this sector in Luxembourg.

Business – value creation

The objective of the IFSB and FRESH is to develop a pilot and a proof of concept that such projects can be financially sound. Future consumers are expected to be (in a first phase) IFSB trainees and employees. The rest of the production should be sold in a short supply chain. Financial balance should be achieved by diversifying activities in collaboration with the future operator.
The fault in this reasoning could be the planning of a profitable production although the greenhouse area is relatively small. Therefore, it will be necessary to capitalise knowledge on all future achievements in Luxembourg and elsewhere.  Nevertheless, fresh fruit and vegetable production – fully dedicated to local needs – will remain a very positive factor.
On the other hand, CO² is becoming a cost factor for the building sector. Luxembourg’s government is currently planning to tax CO² emissions from buildings. This could be a valuable selling point for future promoters willing to find solutions for a better environment. 

This other goal will be to emphasize that the CO² footprint of buildings can

be lowered by making the construction and farming sectors work together.

The IFSB will provide an example of the construction of an efficient greenhouse

that complies with the principles of circular economy. The life cycle and future

dismantling of the RTG will be optimised, as well as upcycling of the materials.
Another target is to establish a link between the education and construction

sectors to anticipate the country's needs – CO² management, food resilience,

education, training, etc.
The greenhouse will not only be used to produce vegetables, but above all to

exploit possible synergies with the restaurant below (CO², energy, social interactions,

With this project, the IFSB will offer training courses for people involved in the

construction and farming sectors.



The construction of the restaurant and the greenhouse on its roof will comply with the principles of circular economy. A large part of the structure will be simple and robust, while allowing for simple future dismantling.  Following this simple design logic, a metal frame and glass walls will be used. These materials are very easily reusable and recyclable. The principle of simple vertical load-bearing elements with fillings in-between allows fast construction, easy modifications, and low-cost renovation if necessary.
The load-bearing capacity is not a problem since the slab was designed with an overload of 500 kg/m² (5 KN/m²). The slab on which the greenhouse will be built will be made of concrete. More precisely, it will have a mixed structure – steel concrete. This will allow great freedom for building the greenhouse. As the building is not very high, the wind load is not too high. Nevertheless, we have to consider the connections with the existing building. The deformations of the part of the greenhouse in contact with the existing building (north facade) should therefore be strictly controlled.
Waterproofing issues are quite tricky because the material has to be resistant to wear and tear and shock, while being stable and easy to maintain. The option of a sealing protected by another material is also considered: waterproofing can then be an unbounded membrane with a protection.  The structural connection with the building underneath will also be studied so as not to interfere with the load-bearing structure or the waterproofing of the roof.
For the greenhouse, a light metal structure and walls with a good degree of insulation will be prioritised since the greenhouse will be heated. Steel allows for a slim structure that casts minimal shadow. Glass is resistant, with a good degree of light transmission. Double glazing transmits less light but provides better insulation for the greenhouse (U=1,2 W/m2K). Nevertheless, double glazing achieves a light transmission of +/- 89% with the new available materials.
The greenhouse will be built in the city. It will also have to be aesthetically accepted and even add value to the building. The typical profile of greenhouses seen outside cities may therefore not be suitable and require a dedicated coating. The RTG will have to be aesthetically accepted and bring added value.
Construction risks will be mastered by the IFSB’s expertise: efficiency, safety measures related to maintenance and accessibility are all elements taken into consideration for this project. All calculations will be performed in accordance with Eurocodes.  This means that the experiments will be easily reproducible throughout Europe.

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Energy management

Before studying the energy savings of the greenhouse, we need to know exactly what the adjacent building has to offer in terms of energy and CO². Thus, air flows from offices and classrooms have been identified and are monitored. We also studied the emissions/flows from the kitchen and the restaurant to re-inject them into the greenhouse.  These air emissions could bring thermal energy inside the greenhouse from air that is 3 to 6°C warmer than the outside air (according to the first results of monitoring carried out in autumn). The monitoring of the greenhouse will allow us to quantify the energy gains brought by air from the ventilation of the building.  In addition, this air will be more CO² loaded since it will be extracted from the interior of the building where many people are trained. CO² emissions will be monitored to know the recovered quantity and the “cleaning” effect of the air (less CO², more oxygen). This inter-connection of building structures is also positive for plant growth because CO² is the main feedstock of photosynthesis.

On the other hand, it will also be possible to use the greenhouse to heat the building. This will be achieved through less energy loss through the roof of the restaurant and through the south side of the IFSB auditorium. This gain is difficult to monitor but we can study it from a theoretical point of view.

For the greenhouse itself, different elements should be studied.

  • The walls of the greenhouse will have a double glass layer (U=1.2 W/m²K) to guarantee better insulation.  Calculations made over a period of several years clearly show that, for a heated greenhouse, savings mainly come from wall insulation.

  • The building will be designed to be potentially dismantled in the spirit of circular economy. The materials – glass, steel, and concrete (for the foundations) – are easily reusable or recyclable. The quantity of CO² used to manufacture the materials used to build the greenhouse will therefore be evaluated.

  • The greenhouse itself will be designed to reuse the CO² and heat emitted by the IFSB building. As for heating, we will take advantage of the greenhouse construction to replace the current pellet boiler by a more powerful but also more efficient one. Finally, to complete the "green" energy supply of the greenhouse, the largest possible surface area of photovoltaic panels and a few thermal solar panels will be installed.

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The production initially planned in the greenhouse was exclusively oriented towards quality tomatoes grown on MG® multi-gutters made of steel coated with polyester. The maximum load on each gutter is 15 kg/m.

The greenhouse will be heated by hot water pipes distributed over the floor and at the foot of the perimeter walls to enable year-round production.

In a second phase, assimilation lighting is planned for better tomato growth in winter. This will require blackout curtains on the greenhouse periphery and ceiling.  These are expensive but mandatory (light pollution is prohibited). In order to ensure a constant climate throughout the greenhouse, we a mechanical air circulation system will also be installed.

Hydroponic cultivation is relatively simple to organise and will allow us to:

  • work with a single climate,

  • work with a single fertilisation system

  • take advantage of the great height of the greenhouse (7.5 m)

It appeared in the business model that it would be difficult to achieve sufficient profitability with a monoculture.  We therefore adapted our project by keeping half of the surface in hydroponics for tomatoes, while the other half will consist of "tower gardens" where other vegetables will be grown. Of course, these crops (e.g. cucumber, pepper) will have to adapt to the climate control designed for tomatoes.

The expected climate for vegetables is above 18°C. Production will take place over 11 months from end of January to end of December. This will leave us one month to do the cleaning and maintenance necessary for the proper functioning of the greenhouse and will avoid heating during the coldest month.

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