In practice, a variety of concepts exist, combining circular design qualities in an intelligent way, adapted to the specific context of each project. Here we collect some typical ones.
Pace-layering is a design concept that organises building components with a different durability in separate layers. Organising these layers in such a way that a layer with components of a shorter service life is independent from, and more accessible than, a layer with components with a longer life span, allows preserving the components’ integrity during subsequent alterations. The regularly cited layering concept ‘Site, Structure, Skin, Services, Space Plan and Stuff’ was formulated by Steward Brand but the concept has also been studied by Francis Duffy and Bernard Leupen.
Pace-layering is not new. It was Nikolaas John Habraken who argued for a distinction between just two basic layers: the multi-purpose base building, called ‘support’ and the fit-out, called ‘infill’. His distinction is foremost one of design responsibility and only secondarily a technical one. Further, in heritage projects new interventions are frequently independent from, and connected in a reversible way to, the existing structure to preserve the latter’s value. As another example, in the Swiss canton of Bern, the Systemtrennung directive requires designers to separate ‘skin’, ‘structure’ and ‘services’ in all public buildings.
Kit-of-parts is a design concept that proceeds from systems of durable, multipurpose, compatible and manageable building components, like Meccano toys. Those components are shaped according to a set of dimensional standards and assembled in a reversible way, optimising their production and construction process, facilitating their stock management and increasing their reuse potential. As illustrated by the construction kits of for example Jean Prouvé or the Cellophane House of Kieran Timberlake, whole-kit buildings are useful for specific purposes, while kitchen systems and office partition walls are kit-of-parts that are used and reused every day.
The kit-of-parts concept can be extended from individual to multiple building systems. If the components of different producers are designed in such a way that they can be combined and reused in multiple building projects thanks to mutual agreements on the components’ shape and dimensions, we speak of an ‘open building system’. As discussed by Frank De Troyer and Asko Sarja, open building systems do not have the intention to standardise solutions through simple modularity, but to increase reuse possibilities by maximising compatibility.
Designing buildings as material banks approaches the built environment as a stockpile of valuable components, waiting to be reclaimed whenever the building that hosts these components becomes obsolete. To enable the reuse of building components, it is necessary to use durable materials, keep the overall design simple and make connections as reversible as possible. The Dutch architectural office Superuse Studios is forerunner in reuse and demonstrates its feasibility in projects like BlueCity and REwind Rotterdam.
The buildings as material banks concept can be extended further to the idea of urban mining, considering cities as quarries of ‘raw’ materials that can be recycled into new construction products. Considering the local availability of those materials, their purity, safety, overall ease of recovery and the existence of suitable logistics, might serve as useful guidelines towards the feasible implementation of this urban mining concept.