“(…) es posible valorar la idoneidad de una planta antes de su ejecución. Así, por ejemplo, recorridos de circulación breves pero intricados ocasionan un desgaste de energías físicas […], los cruces de circulaciones imposibilitan el desarrollo simultáneo y sin interferencias de las principales actividades que se realizan en la vivienda: cocinar-comer, dormir-lavarse, trabajar-descansar. Los espacios de comunicación demasiado grandes y los recorridos demasiado largos que se derivan de una desfavorable distribución de la planta provocan un aumento de la superficie.”
(Klein, p.33) 
In the period following the First World War, there was a need to build on a massive scale and as quickly as possible. Housing had to achieve maximum efficiency – Klein carried out an exhaustive study on how to achieve the minimum dimensions for the proper functioning of each space. His methodology was presented for the first time in Paris, in 1928, and the following year at the 2nd CIAM, in Frankfurt. In 1930, the government of the Reich decided to fund housing construction and established that the area of each housing unit should be between 32 and 45 sqm.
The following is an example of how a residential unit was assessed. The models in Figure 1 show plans for common housing units, with 3 and 3 ½ bedrooms. On a functional level, they contain the following errors, according to Klein:
– on the first plan, spaces are not grouped according to their functions: there is no clear link between the bathroom and bedrooms – the two functions that constitute the night-time part are not together. The unsuitable placement of the bedroom creates routes that intersect when they should be independent.
– on the second plan, again, the grouping of the spaces is not good; they do not adhere to the separation between daytime spaces, on one side, and night-time spaces on the other; the bathroom is not located near the bedrooms, which means an intersection of routes between the night-time and day-time zone.
Figure 1 – Alexander Klein – plans that contain errors on a functional level, according to Klein
The two models in Figure 2 correspond to Klein’s corrections to the models presented in Figure 1.
Figure 2 – Alexander Klein – functional assessment of the plans shown above.
In the first plan (Figure 2, left-hand side), Klein divides the house into two zones: a daytime zone (with living room and kitchen) and a night-time zone (with the bedrooms and bathroom). The living room and the entrance hall form a single space, with the possibility of separating them with a curtain or a glass door. The hall marks the separation between the two zones and, from it, both can be reached independently. There is no intersection of routes between the daytime zone and the night-time zone. There is a smaller kitchen area and a larger living room area. The beds are placed in the innermost part of the bedrooms, that is, the quietest part. The furniture is concentrated, with no loose pieces. The sanitary installations are reduced to the smallest size possible, containing only a basin, toilet and bath.
The second plan (Figure 2, right-hand side) corresponds to a refinement of the first through graphic analysis – it changes the layout of the furniture in the master bedroom; it creates a direct link between the master bedroom and the dining area.
Klein separates the inside of the house according to the following binomials: cook/eat; sleep/body care; leisure/rest. In addition to this, he adopts a division of the house into two more general parts: the private/night-time part (formed of the bedrooms and bathrooms) and the more public/daytime part (formed of the living room, dining room and kitchen).
Klein analyses the functionality of the housing unit using graphs to study various relationships, the most important being the one that looks at the different routes and intersections that the resident might make inside the house.
In Figures 3a and 3b, Klein shows the functional problems of the unit in question – he criticises the fact that the routes of the binomials intersect.
Figures 3c and 3d show a correct drawing of the routes, that is, the layout of functions within the house, in which the binomials do not intersect: from the entrance, one can go directly either to the bedroom+bathroom zone – sleeping/body care binomial – or to the kitchen zone – cooking/eating binomial – or even to the living room – rest/leisure binomial.
Figure 3a – example of housing unit that is incorrect on an organisational/functional level – night-time routes intersect with daytime routes.
Figure 3b – example of housing unit that is incorrect on an organisational/functional level – night-time routes intersect with daytime routes.
Figure 3c – example of housing unit that is correct on an organisational/functional level – night-time routes do not intersect with daytime routes.
Figure 3d – example of housing unit that is correct on an organisational/functional level – night-time routes do not intersect with daytime routes.
Alexander Klein – analysis of routes and intersections within the housing unit according to the graph method (red = daytime routes / blue = night-time routes).
There is a new reading of the living space: if it must be reduced to the smallest possible dimensions, Klein believes there must be maximum functionality, both inside each room and in the relationship between rooms.
Figure 4 – Alexander Klein – division of the house into two zones – daytime (grey) and night-time (blue).
These binomials redefine the architecture of the residential unit: the domestic interior is now organised according to ‘pockets’ (each pocket corresponds to a binomial) that are independent from each other, the routes of which should not intersect. The house is divided into two parts: the day-time zone (which contains the kitchen, dining area and living room) and the night-time zone (containing the bedrooms and bathroom). All reduced to a minimum, in terms of both space and circulation. Consequently, there is a limited and diminished possibility of the occupant appropriating the space.
Klein’s methodology was his response to the massive and immediate need for construction. But even today, these rules still exist in most architecture for collective dwelling: the quality of the dwelling is taken as a synonym for functionality.
As architects, let us reflect on the way we are designing the spatial use of the housing unit.
 ‘(…) it is possible to assess the suitability of a plan prior to its execution. In this way, for example, small but intricate circulation spaces lead to a waste of physical energies (…), the intersection of circulation routes makes it impossible to carry out, simultaneously and without interference, the main activities of the house: cooking-eating; sleeping-washing; working-resting. Circulation spaces that are too large and hallways that are too long, resulting from an unfavourable layout on the plan lead to an increase in area.’ (our translation)