Good design decisions are not made in isolation and nor do they ‘solve’ one problem at a time. A good design decision should have three reasons motivating it (structural, functional, economic, constructional, ergonomic, light based, etc.). One of the three should be an architectural reason. An example is the choice of vierendeel trusses in the Orphanage designed by Aldo van Eyck. These feature a horizontal void in the centre of the concrete beams. This design decisions accomplishes at least three things: 1) the void makes structural
sense since the middle of the bean takes the least stresses (structural); 2) the void lightens the weight and cost of the concrete (economic); 3) the void when filled with translucent glass allows for light to enter at a juncture that lights the space physically and lightens it visually (architectural). This last effect is achieved because diffused light is allowed to enter at a juncture where the roof meets the wall, making the roof and its weight appear to float.
The point behind the idea of ‘3 reasons’ is to try to link up decisions across criteria. The more you link up, the more efficient your design is, and the more defensible it is since you can call up several reasons for having made a particular choice. This is obvious not possible with every single design decision – but you will be surprised how many you can do in this way once you get into the habit of trying. The reason for one reason being architectural is to remind you that design decisions are not all based on pragmatic or functional grounds. You should always try to see what the architectural potential is of any pragmatic demand (structural problems, health and safety regulations, accessibility requirements, etc.).
Source: This was a challenge posed to me by the architect and teacher Henri Ciriani during a design tutorial. The example of the orphanage is also his.