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A technical, economic, social, and environmental assessment determines the rationale and effectiveness of any project. Circularity evaluation should be performed as part of the environmental assessment to more objectively support the decision-making process by considering the latest trends in implementing sustainable development principles.
To date, no standardised methodology has been developed to measure building circularity, and existing ones and still under discussion and vary in terms of the scale of application, the scope adopted, and the definition of circularity. This is why we propose a new, simplified, yet comprehensive take on the problem but build upon existing knowledge and developed measurements so far.
The developed Circularity Index (CI) describes the various elements of circularity expressed by sub-indicators covering the entire lifecycle of the building. The sub-indicators are:
The SMU includes the materials/elements used for the construction, the MRP is related to the end-of-life stage of these materials/elements, and the SR and SSP concern the building operation phase.
More about these indicators and methodology for calculating the final Circularity Index (CI) is shown in separate sections below.
Minimising the use of primary raw materials is one of the pillars of circular construction, so one should strive for a situation in which new buildings are constructed from reused and recycled materials and elements and designed to make future reuse and recycling of these materials and elements possible.
Various materials, however, differ qualitatively in terms of their scarcity, availability, or associated market value. This is why it is reasonable to include these differences in circularity evaluation to more reliably assess the environmental impact of reusing or recycling specific materials and elements. One way of doing it is by using the Abiotic Depletion Potential (ADP) factor based on individual raw materials’ consumption and global resources.
We can say that ADP measures the “environmental value” of using given material in the circular economy context in which the impact on resource depletion is fundamental. For example, let’s say we have two materials and want to determine their environmental impact. In economic analysis, to know each material price, we would have to know the quantities of the material (e.g., m3) and their unit price (e.g., EUR/m3), and based on these, we could calculate their value expressed in EUR. Similarly, in a circular context, knowing the quantities of material and their ADP (kgSbeq./m3), we can get their “environmental value” expressed in kgSbeq.
The Secondary Materials Use indicator (SMU) measures the share of saved primary raw materials through using secondary materials from reuse or recycling. SMU also includes the materials or elements’ environmental value considering their scarcity through incorporating the Abiotic Depletion Potential (ADP) values for each.
To further promote good practices, SMU also acknowledges the differences between the environmental impact of reuse, upcycling, recycling, and downcycling by assigning different weight factors to them. In the circular economy, reuse is preferred over recycling as the other requires additional processes, increasing its toll on the environment.
SMU is calculated as a sum of all the materials and elements listed in the inventory:
where:
The values of Wj weight factors were developed based on the discussions with a panel of experts from the construction industry and are as follows:
Reuse: Wreu = 1
Upcycling: Wupc = 0.7
Recycling: Wrec = 0.6
Downcycling: Wdown = 0.3
The ADP values are not always easy to obtain. If no such data is available, the simplified evaluation methodology can be adopted, which does not consider the environmental value of individual materials due to their availability in the environment. Thus, such a solution has disadvantages, but sometimes it may prove to be the only option with limited availability of information.
Then, the simplified SMU can be calculated as follows:
where:
The following materials and elements were used for construction:
| Material / element | Mass | ADP | Origin |
|---|---|---|---|
| Cement | 5 t | ADP = 1.10e-06 MgSb/t | entirely primary material |
| Sand and gravel | 40 t | ADP = 2.26e-09MgSb/t | 30 t of primary material and10 t from reuse |
| Bricks | 40 t | ADP = 1.13e-07MgSb/t | 10 t of primary material and30 t from reuse |
| Fabricated metal components | 4 t | ADP = 3.79e-06MgSb/t | 2 t of primary material and2 t from recycling |
For such data, the SMU calculation looks as follows:
The obtained value means that the evaluated design is circular, considering the use of secondary materials in 31.5%.
Note that the calculated indicator should capture all materials and elements of the building under evaluation. The above example is simplified for clarity of the message.
For the same data, the SMUs (simplified indicator) calculations look as follows:
The Materials Reusability Potential indicator (MRP) describes to which extent the materials used in the building construction can be used in the future and thus contribute to resource conservation. It is, therefore, a measure of the potential for future use of materials used in construction.
The indicator in its design is similar to the SMU indicator. It considers all building materials and elements with their Abiotic Depletion Potential values. Unlike SMU, however, it concerns the future possible use of the materials and elements rather than their origin.
Similarly to the SMU indicator, MRP covers the differences between reusing, upcycling, recycling, and downcycling by assigning various weight factors to them.
MRP is calculated as a sum of all the materials and elements listed in the inventory:
where:
The values of weight factors were developed based on the discussions with a panel of experts from the construction industry and are as follows:
Reuse: Wreu = 1
Upcycling: Wupc = 0.7
Recycling: Wrec = 0.6
Downcycling: Wdown = 0.3
The ADP values are not always easy to obtain. If no such data is available, the simplified evaluation methodology can be adopted, which does not consider the environmental value of individual materials due to their availability in the environment. Thus, such a solution has disadvantages, but sometimes it may prove to be the only option with limited availability of information.
Then, the simplified MRP can be calculated as follows:
where:
The following materials and elements were used for construction:
| Material/element | Mass | ADP | Origin |
|---|---|---|---|
| Bricks | 30 t | ADP = 1.13e-07MgSb/t | 10 t can be reused, and 20 t can be recycled in the future |
| Plasterboard | 2 t | ADP = 4.29e-07MgSb/t | 1 t can be recycled in the future |
For such data, the MRP calculation looks as follows:
For the same data, the MRPs (simplified indicator) calculations look as follows:
The value of the simplified indicator MRPs is higher than that of the MRP indicator, but MRPs does not include the different environmental values of the materials/elements (their scarcity).
As a part of circular design, the space’s adaptability should be considered, which means that its transformation to various functions without causing major reconstruction work, demolition, and material losses should be ensured.
Three main types of possible transformation can be distinguished, namely: monofunctional, transfunctional, and multi-dimensional[1].
SR describes the extent to which a building’s floor space can be used in other functions than planned initially and is defined as follows:
where:
The values of weight factors were developed based on the discussions with a panel of experts from the construction industry and are as follows:
The total usable area of the office building is 1200 m². It was designed so that a significant part (1000 m²) could be easily transformed and adapted to several purposes but falling within the scope of office activities. The rest of the building is fully adaptable to various different functions – so it can be used as an office but also for residential purposes. The building has such a structure that there is no possibility of changing its shape and size. It means that 1000 m2 in this building can be transformed monofunctionally and the rest (200 m²) multi-dimensionally.
For such conditions, the SR calculation looks as follows:
Sharing space is essential in a circular economy as it reduces the need for new constructions by optimising the use of existing ones. As a result, this leads to a considerable reduction in the consumption of mineral resources.
SSP describes the extent to which a building’s floor area can be shared between the tenants (or any other groups or organisations in the building) and is defined as follows:
where:
The total usable area of the office is 60 m2, and it is divided into two parts. In the first part, there are built-in cabinets and massive desks. In the second part (29 m2), the area is free of installations and permanent objects, so it can be shared.
An entirely circular building is one for which all sub-indicators (SMU, MRP, SR, SSP) reach the highest value, i.e., 100%. However, achieving 100% is unfortunately difficult (even objectively impossible). This is why choosing a scenario with the highest possible total circularity in the circular design is the most optimal way to go.
In circularity assessment, unambiguous and straightforward cases might happen. For example, let’s say we are considering two different scenarios for the building design, and we calculated the sub-indicators (SMU, MRP, SR, and SSP) for both. In the first scenario, two sub-indicators have a very high value, and the remaining ones are almost 0%, and in the second scenario, the opposite occurs. Which scenario is more circular?
To solve this issue, the weighting factors for each sub-indicator were introduced together with one single indicator (Circularity Index – CI) based on all sub-indicators to aid the final decision process.
In the proposed methodology, sub-indicators related to materials (i.e., SMU and MRP) are valued separately, each with a weight factor of 0.33. On the contrary, the indicators relating to the utility and functionality of the building area are considered collectively, and their combined weight factor is 0.34. Such an approach was adopted due to the partial functional similarity of the two sub-indicators.
The CI circularity index is determined using the sub-indicators:
where:
The values of weight factors were developed based on the discussions with a panel of experts from the construction industry and are as follows:
The sub-indicators were calculated for the building, and their values are as follows:
For such data, the CI calculation looks as follows:
[1]BAMB – Building as Material Banks, Reversible Building design guidelines, 2018