How to dimension a building intended in particular to study plant growth. How can it be organised knowing that it is installed on a hollow tooth 8m by 50m deep? The company Biostransfer, private project owner, contacted us for the design of this project. Each new subject is for us an opportunity to immerse ourselves in the daily life of different people and in practices that are unfamiliar to us. There is always this moment of learning which is interesting and allows us to extract the fundamental elements of a profession and the other satellite elements which can be considered as common to other uses, other actions, other spatialities. We carried out two preliminary feasibility studies on two different sites for this same programme before the Biotransfer company finally moved towards this site. It was interesting to observe the variations of the same programme on three totally different plots, in different built and PLU contexts. The project quickly turned out to be quite technical, particularly in terms of natural light management, ventilation and hygrometric regulation. Consideration was also given to staff movement and transit between rooms. Some rooms required special protection, others were dark, damp, hot or outside. The challenge was to keep in mind that the construction could one day have another use if the company were to resell the property. The double heights and the necessary patios were real opportunities for us in the idea of developing domestic spaces in the future. The patios intended to receive the largest plant subjects were thought to eventually serve as skylights for offices or apartments that would come to occupy the floors in a second life. The project was developed up to the APS stage before we learned that the town hall was pre-empting the plot. It was a clear stop and a real frustration for our agency because the Biotransfer company, after having tried to acquire a third plot, gave up building to transfer its premises. It is a subject that fascinated us because it is the very essence of the way we see architecture. Concise but plural, efficient and evolutionary.