4.1. Design Preconditions
In this section, preconditions are formulated. The starting point is the assumption that a critical level of flexibility is accommodated by the super-structural design of a multi-family property. The residents of each individual housing unit are free to define the whole infill layout, and thus also the type and location of room dividing partition walls. In order to anticipate change, the partition walls should not obstruct any potential future intervention, be it due to infill rearrangements, maintenance, repair, replacement, or upgrades. Circularity of associated parts-building components, materials, and raw materials-needs to be respected at all times. Those parts can thus not be seen in isolation but always in relation to provenance and destination, underscoring the relevance of value chains and the distribution of control. The design brief takes a user-centered approach, adhering to healthy building and renovation concepts that allow for a high level of flexibility regarding the space layout, whilst striving for high circularity potential of the associated materials. The focus is on a non-bearing partition wall. Below, specific preconditions are listed that integrate intrinsic properties of the partitioning part, as well as relational properties, with regard to user experience, physical context, and value chain performance, based on Geldermans et al. [3
The partitioning wall unlocks flexibility-capacity, through ease of assembly, disassembly, reassembly, and reutilization;
The partitioning wall unlocks circularity capacity, through the ease of maintenance, reuse, redistribution, remanufacturing, recycling, and/or facilitating biological cycles;
The partitioning wall unlocks user capacity, by an inclusive approach that takes account of willingness to engage, freedom of choice, and the health and well-being of end-users;
The partitioning wall supports coordination between subsystems, particularly in regard to installations and electric or data provisions;
The partitioning wall accommodates multiple duty ratings.
All preconditions originate in Circ-Flex assessment guidelines, although preconditions one to three are more explicitly addressed than four and five. The latter two, however, represent aspects that are no less relevant for the conceptualization exercise. Precondition 4 highlights the fact that partitions ‘communicate’ with adjacent parts, such as doors and ceilings, as well as mechanical, electric, plumbing (MEP), and information and communication technology (ICT) infrastructure. Precondition five is based on the level of duty the partition should be able to support, in case present or new-users and/or functions require a different performance profile. For example, when compartments change from a domestic duty to office functions. Although the options are virtually limitless, and heavier duties could be imagined with regard to the required performance, a typical ‘medium duty’ is assumed, compatible with categories A and B of the Eurocode “Action on Structures” [40
]. This resonates in, amongst others, fire, thermal, and robustness performance. Precondition five implies a certain level of product-familiarity: Neutral enough to withstand forces of change, both from the perspective of users and building owners.
4.2. Frame of Reference
The design conceptualization departs from familiar examples of residential floor to ceiling wall systems that are easy to assemble, disassemble, and re-assemble, but robust enough to function in a (semi-)fixed setting. In the Dutch context, two primary partitioning variants apply in this respect: A configuration based on-homogeneous or heterogeneous-solid wall modules, in which framework, insulation and cladding are incorporated, and a hollow variant based on a studwork with separate side-panels and insulation. In the latter configuration, the framework is comprised of either timber or metal studs. Eventual finishing layers are not part of the conceptualization, even though these may have a strong impact on circularity, flexibility, and health performance. This will be addressed in the discussion section. Figure 3
displays a solid partitioning wall configuration (a), and its hollow counterpart (in the metal stud variety) (b).
Considerations concerning changing requirements for cables and wires have been addressed in the past, and solutions have found their way to the market. Infill Systems BV (with a branch in The Netherlands and the United States of America), for example, has patented multiple variations relating to “invisibly arranging cabling in an indoor space defined wholly or partially by non-load-bearing partition walls” [42
]. Those patents are rooted in the notion of open building and the flexibility of the space layout, as addressed in Section 2.1
, with a long history of research and implementation [43
]. Moreover, several manufacturers of partitioning products have integrated those notions into their products. An example is the ‘Cable Stud,’ by the aforementioned Infill Systems BV, especially developed for hollow metal stud wall configurations that anticipate optimal freedom for positioning of installations and associated infrastructure. Variations on this innovation can be found in, amongst others, the Knauf BoWall system, and the Faay KBL system. The latter is developed for a solid wall system. In contrast to hollow-wall systems, solid walls reduce the flexibility with regard to placement of, for example, MEP and ICT provisions.
Regarding the materialization of hollow-wall partitioning, the main roles are claimed by the boards used for side-panelling and the insulation material within the cavity between two boards. A primary product with regard to side-panelling is gypsum board, which is widely used for partitions [50
]. Gypsum boards are an example of materials that can function in circular models, consisting primarily of recyclable calcium sulfate dihydrate (CaSO4
O). Although recycling rates are still relatively low on a European scale, the Netherlands shows increasingly high scores, induced by more stringent regulations that prevent transboundary landfilling [51
]. Yet, an orchestrated effort is still required to fully capitalize on the recycling potential of gypsum-based waste. A recent study into the benefits of deconstruction (and segregated disposal) versus demolition (and disposal in mixed waste) showed that the latter is significantly more costly [50
A small percentage of the weight of the gypsum board product (usually 1–5% for a basic board, but more if specific properties are required) consists of additives, such as binding agents, process accelerants and retardants, fillers, reinforcement fibers, fire retardants, and foaming agents [52
]. Those additives are not regenerated to their initial quality, and become an impurity in the gypsum-recycling process. Moreover, other impurities may accumulate in the secondary gypsum flow along the way, adding up to about 10% of impurities in total. Although most substances can safely be integrated in the production processes, a certain level of gypsum-purity is required [53
]. This necessitates the addition of purer gypsum. Gypsum recycling is thus essentially downcycling.
Flue gas desulphurization (FGD) gypsum is currently the main raw material in gypsum boards for the Dutch market [54
]. In light of the imminent phase-out of coal-fired power-plants as the primary source of FGD gypsum, other sources need to be explored, apart from increasing the share of recycled gypsum [54
]. Most likely, this will lead to natural mines in, for example, Morocco, Spain, or France. Another source would be so-called Phosphogypsum, formed as by-product in fertilizer production. This raw material, however, is controversial due to its-weak-radioactivity, and is currently not broadly accepted as a safe alternative [55
Concerning insulation materials, mineral wool (or man-made vitreous fibres: MMVFs) is—and has been—widely applied in Dutch construction. In current demolition flows, rock wool is more common than glass wool, as the latter entered the market later [56
]. There are reported health threats associated with mineral wool, in particular in manufacturing, construction, and deconstruction or demolition stages, but exposure may also occur during do-it-yourself home remodeling activities [57
]. As yet, there is no substantial evidence regarding human toxicology of mineral wool. Certain MMVFs have been classified as carcinogenic in the past, by the World Health Organization. However, this classification was withdrawn after the manufacturing industry altered the composition of their product [58
]. Currently, multiple sources report the statis: ‘Reasonably anticipated to be human carcinogenic’ for glass wool [59
]. In the Netherlands, there are several facilities that recycle mineral wool at a high-grade. This requires appropriate disposal and logistical management, which is not widely applied yet, neither in the Netherlands nor in Europe as a whole [61
]. Although nowadays not as widely used as their mineral counterpart, cellulose wool has been applied in partitionings’ constituents for a long time, whilst becoming increasingly sophisticated [64
]. Not many data are available with regard to whole lifecycle performance of contemporary cellulose materials, but LCA-based studies detect advantages and disadvantages regarding the—environmental—performance for cellulose insulation products, such as paper wool [64
]. From the viewpoint of flexibility and circularity, uncertainties regarding the end-of-life stage are promonent obstacles, whereas—human and environmental—health issues are related to dust and additives [64
]. A Dutch manufacturer of recycled paper insulation products (Everuse®
), has tackled the end-of-life issue to some extent, by retaining ownership and taking back the products after an agreed functional life [67
]. The issue relating additives, however, remains unsolved.