In the Mollier Houses project (2005), vacation homes designed for the Vassivière Lake in the Limousin region of France, Philippe Rahm took into account the humidity levels in the air, its management and its temperature inside the habitat. Here, the distribution of spaces does not follow the traditional layout based on day/night, public/private, but rather a logic drawn from specific sensual and physiological phenomena. The amount of water vapor a home produces depends on the level of activity in a particular space (for example, when asleep, a person produces four times less water vapor than someone involved in an activity: awake, the occupant uses hot water, etc.). Rather than solve the problems caused by humidity only using the ventilation systems, Rahm created spaces based on variations in humidity levels, from drier to more humid, from 20% to 100% relative humidity. “The quality of the architecture is determined by the amount of water vapor in the air, like a real immersion of the occupants’ bodies in the humid and variable shape of the space.” Rahm drew inspiration from the Mollier diagram—utilized in thermodynamics to measure increases in energy produced by a variation in temperature or the change in the state of a fluid. He translated this spatially through hygrometric stratification and by correspondences in the program which make it possible to use the same space to house different functions. Rahm eschews a fixed functional programming of space; proposing variable spaces instead, more or less dry, more or less humid, to be occupied as desired according to the season. The project also extends this hygrometric stratification beyond the confines of the house to the landscape, turning the physical presence of the lake into a potential room, with 100% humidity.