Opaque cylindrical shaped building as shown in the figure can be considered as the highest achievable design configuration from energy and moisture performance perspectives. Simple designs are less intricated and are easy to achieve continuity of building control layers. For the same floor area cylindrical shape has less surface area than other shapes, which translates to less heat loss, followed by cuboid. Windows are the leakiest component of a building from energy perspective, where significant amount of heat loss and gain occurs, as a result a cylindrical shaped building without this component as shown in Figure a) can be considered as the highest achievable performance.However, enclosed spaces without windows are not different than cages; as a result for practical reason the concept of opaque design can’t be implemented, and makes practical buildings deviates from this maximum achievable performance. The more a building differs from this ideal configuration the highest the deviation from the maximum performance. Which is demonstrated in the figure below where performance reduces from a) to e) where windows to wall ratio increases and shapes deviate from ideal conditions.
Figure: Building configuration versus building performance