OS House allowed us to put an architectural experiment into practice. The owners challenged us with a program of unusual complexity for this typology that reflected very differing needs. Firstly, a possible variation in the number of users of the house, from 2 to 30 or more, and all the possibilities between. Secondly, the usual seasonal variations in a second home were exacerbated by the number of users. A final factor that was introduced into this array of possibilities was the uncertain future of this program. The owners’ age, the future growth of their children’s families and a possible change from second to first home were the final factors in a situation to which we had to respond with clockwork precision and, at the same time, with sufficient slack to accommodate changes in the programme that cannot be identified in advance.We quickly realised that the experiment should centre on the search for a model of floor plan that would absorb the contemporary time flows expressed in the demands of the program and we were able to recite our working hypothesis: to explore the possibility of organizing a complex domestic space by means of the simple addition of basic spaces.We defined the limits of a work plan, addressing decisions of scale and relation with the setting, and the stipulations of planning regulations. We came up with several models, adjusting surface areas, wall thicknesses, systems of spatial relation and conditions of use, till the process gelled at a point from which we extracted the definitive solution.Let’s take a recount: the floor plan of the dwelling is made up of 30 basic spaces associated in 48 simple pairs and 132 complex relations. The basic spaces represent a fragment of the program and a degree of uncertainty. For example, we have the ‘kitchen’ space that will probably continue to be the ‘kitchen’ space for a long time. The uncertainty in this case is nil. But then we have spaces such as the ‘large south living room’, which has a high level of uncertainty because it could be a dormitory, a children’s playroom or a winter living room. The most extreme case of uncertainty centres in the north and south hallways, because as yet no one knows what they will be used for, through various proposals have been made. The simple pairs comprise two basic spaces joined by an empty floor-to-ceiling space. The complex relations are those that include an itinerary between two basic spaces via a third. The system of addition has had some comforting effects on the spatial complexity of the dwelling. The floor plan of OS House is defined as a field of multiple possibilities.