Introduction

The EU Horizon 2020 funded CityLoops project focuses on closing the material loops of two central sectors of any city in terms of material flows, societal needs and employment, namely the construction and biomass sectors. Due to their sizes, they represent a considerable opportunity for cities to transform their metabolism and economy towards a more circular state.

Within this project, seven European cities, amongst those also the City of Høje-Taastrup are planning to implement demonstration actions to kickstart their circularity journey. To better understand what the current circularity status quo is, as well as the impact of these actions, and the efforts needed to transform their sector, a Sector-Wide Circularity Assessment method was developed. This method combines a circular city and circular sector definition, a material flow and stock accounting method, as well as circularity indicators. The sector itself was defined in terms of a number of representative materials that make up a large share of the sector and associated economic activities. The construction sector is made up of 11 materials, depicted as icons here, which were studied along the entirety of their supply chains. Altogether, these elements help to set a solid knowledge and analytical foundation to develop future circularity roadmaps and action plans.

The assessment was carried out by the cities themselves after receiving extensive training in the form of courses on data collection (construction and biomass) and data processing. Numerous additional insights can be found in the individual Data Hubs of each city.

This current Sector-Wide Circularity Assessment report provides contextual information on the city and the economic sector under study. It then illustrates how circular these sectors are through circularity indicators and a Sankey diagram. Finally, it analyses and interprets the results, presents the limitations from the data used and offers recommendations about how to make this sector more circular.

(* The italic texts in this report were written by Metabolism of Cities' Aristide Athanassiadis and Carolin Bellstedt. They provide relevant general information and serve as connecting elements of the single report parts.)

Urban context

To contextualise the results of the sector-wide circularity assessment, this section provides population and land use information data of the city. In addition, population and area of the city under study, as well as its corresponding NUTS3, NUTS2 and country were included. Data for these scales were added to better understand how relevant and important the approximations are when downscaling data from these scales to a city level.

Population of Høje-Taastrup

The population of Høje-Taastrup has been slightly increasing, namely by 6.3%, from 47,753 inhabitants in 2011 to 50,759 in 2020. There were a total of 21,645 households in 2020. Due to urban development measures, the population is expected to further increase to about 60,000 - 65,000 inhabitants in the course of the next 10 years.

As can be seen in the graphic below, the population is comparatively young with half of the population 49.6% of them being 39 years and younger.

Data source

Land use

Data source

The municipality of Høje-Taastrup has two main urban areas, namely Taastrup/Høje-Taastrup and Hedehusene/Fløng. It is in these areas where the main part of the population lives. In addition to these urban areas, there is a large part of the municipality that is rural, with agriculture as well as nature areas.

The land use map of Høje-Taastrup shows 10 different types of land use. It needs to be noted that those are the ones represented in the municipal planning framework of 2014, which do not account for the entire area of the municipality (78 km2), but for 45% of it (34.9 km2). These land uses include general and specific types of residential, business and public purpose areas. The largest share of land is used for residential areas and makes up 10.6 km2 (30.4% of total municipal planned land). The use for recreational purposes is followed by a close second (28.3%) with 9.9 km2. Finally, the business area makes up the third largest share with 21%, while the remaining uses (mixed housing and business, area for public purposes, technical facilities, land area, vacation home area, center, and other) are all below 5%.

With regards to the larger geographical context, “Høje-Taastrup Municipality is located west of Copenhagen and is one of the largest municipalities in the capital area. The municipality covers an area of ​​78 km2 and has no coastline. In the areas around Hedehusene, Fløng, Taastrup and Høje-Taastrup in the central and south-eastern part of the municipality are densely populated with an extensive road network and are intersected by the Holbæk motorway.

Høje-Taastrup Municipality is one of the capital area's greenest municipalities. 2/3 of the area consists of forest, meadow field and lakes with a number of protected areas, including Vasby Mose, Sengeløse Mose and Porsemosen. In many places, especially between Baldersbrønde and Høje Taastrup, around Vridsløsemagle, Sengeløse and Soderup in the north and south of Hedehusene, you can still experience smooth, slightly hilly moraine landscape created by the recent ice age. Smeltevandsdalen Store Vejeådal between Høje-Taastrup and Albertslund municipalities forms an 11 km long green wedge.

The area between the railway and the Holbæk motorway is approx. 20-40 meters above sea level. It then falls to the southeast, north and northwest and is interrupted in several places by meadows and bogs, which in an arc extend from east to west and are drained by Hove Å and its tributaries to Nybølle Å, which flows to the north and forms boundaries to respectively Roskilde and Egedal municipalities.

From Hedehusene, the landscape gradually rises to the south through Reerslev and Stærkende and culminates in the 69 m high Maglehøj. It was for a long time the municipality's highest point, but is today surpassed by the artificial, 81 m high hill Flintebjerg in Hedeland. Where the landscape south of Hedehusene and west of Reerslev and Stærkende previously formed a continuous moraine plain, extensive gravel excavation in the 1960s and 1970s as well as subsequent re-establishment subsequently created a strongly hilly landscape with artificial hills and lakes. Today, the area is Hedeland Nature Park, which extends into Roskilde and Greve Municipality.

Data source

Høje-Taastrup municipality is intersected by a watershed that lies from east to west in a line around the Holbæk motorway. The northern part of the municipality is drained by streams that run northwest to Roskilde Fjord and the southern part of streams that run southeast to Køge Bay. Høje-Taastrup municipality is therefore located at the source of the river systems and therefore has far fewer problems with floods from rivers than the downstream municipalities” (Anja Kiel Groth, groundwater employee of Høje-Taastrup).

Economic context of construction sector

This section puts into perspective the economic context of the sector under study. It describes how many people are employed in this sector, as well as who the main actors involved (from all lifecycle stages for the sector’s materials) are.

The construction sector in Høje-Taastrup

The number of people employed within the construction sector in Høje-Taastrup is slightly increasing. Høje-Taastrup is undergoing urban development in primarily two larger areas but also in other areas in the municipality. Therefore, a lot of construction is taking place. The high construction activity does not necessarily correspond directly to increased local employment in the construction sector as many workers commute to the building sites from other municipalities.

The actors of the construction sector

The primary actors associated with material flows in the construction sector are: Kallerup Grusgrav, NCC Reerslev Grusgrav, IBF Hedehusene, Tscherning, Lind & Risør A/S, F.J. Poulsen's Anlægsgartneri A/S, John Jensen A/S, Dansk Miljøforbedring, Vestforbrænding.

Extraction

Extraction in Høje-Taastrup is handled by two companies, both depicted in the map just above. The first, Kallerup Grusgrav is a company that operates a gravel mine and has been in existence since 1971. The company’s purpose is to extract raw materials from hill materials, among other things for filling / securing roads or backfilling around houses. They also accept concrete and bricks for recycling. The crushed concrete is used just like ordinary stable gravel and bricks are used such as drainage layers at the bottom of riding arenas. They also sell topsoil and lime.

NCC Reerslev Grusgrav is another company operating a gravel pit and is part of NCC, one of Denmark's largest construction and contracting companies. At their site, raw soil, sand, gravel and stone have been extracted for a long time. In the beginning of 2021, NCC Reerslev Grusgrav closed down their activities in the gravel pit, as the area is fully exploited.

Manufacturing

IBF Hedehusene is a large concrete manufacturer, which produces concrete sidewalk tiles, roof tiles, paving stones, retaining walls and ready-mix concrete amongst other things.

Tscherning is a company that operates both locally and nationally and deals with demolition, construction work, environmental remediation and machine rental.

Tarkett A/S is a wood flooring company. They work on the manufacturing and wholesale of flooring. They do have 25 employees at the registered location in Høje-Taastrup, however, only their headquarter office is located in the municipality, but none of their 30 factories. Tarkett currently has approx. 11,000 employees in over 100 countries and had a turnover of approx. 2.5 billion Euro in 2013.

Lastly, there are three companies that deal with the “manufacture of metal structures and parts of structures”. Schrøders Metal A/S is a metal product factory that works as a subcontractor to relevant industries. Established in 1997 and working with 12 employees today, their focus is on the processing of metal sheets, pipes and profiles with the following materials: steel, aluminum, titanium, messing, copper and plastic.

K.S. Smede og Montage A/S, founded in 1986, is a 16 employee large company today. They work on steel and aluminum constructions, handling forging as well as assembly tasks. With their workshop and office facilities in Taastrup, they carry out work for customers, as well as act as a subcontractor to several of the country's largest construction companies.

The third metal working shop is the one of Ebbes Kleinsmedie ApS with 21 employees. It was founded in 1973 and specializes in blacksmithing, sheet metal work, iron constructions and copy cutting, handling iron, stainless steel and finer metals. They are also a regular supplier to the elevator industry with elevator shafts, compartments, frames and doors, as well as industrial painting, assembly and maintenance.

Retail

The main actor within the category of “Retail sale of hardware, paints and glass in specialised stores” is Silvan City2 with 11 employees. The company is a part of a large retail chain of building materials and sells to private and professional craftsmen.

As for the “retail sale of furniture, lighting equipment and other household articles in specialised stores”, IKEA is the largest player in the municipality. Although the company sells a lot of articles, it can be assumed that most of their products are exported into the municipality and that for example, wood is not sourced from the area for their products.

Use

The largest actor for the construction of residential and non-residential buildings is Lind & Risør A/S with 250 employees. Lind & Risør is a 100% Danish family-owned full-service architect and construction company that has built commercial and residential houses since 1980. It provides construction services to customers throughout Denmark. Therefore, it is not known how much construction activities they engage in in Høje-Taastrup.

With regards to the construction of roads and motorways NCC Danmark A/S is a large player, with 19 employees declared. However, as with the other companies engaged in the use phase of construction, their material use (rate) is unknown.

“Landscape service activities” are another activity where construction materials are used. A big actor (around 70 employees) is F.J. Poulsen's Anlægsgartneri A/S. Starting in Roskilde with a horticultural business and nursery in the 1930s and evolving into landscape gardening for private as well as tender business, the company eventually relocated to Taastrup in 2007, to have more space. Nowadays, the company engages in all types of landscape and construction work (sewer, local rainwater diversion, and cloudburst protection, pruning and top cutting, BIO cleaning of lakes, roof gardens and green roofs, concrete crushing & sale of recycled materials, private gardens and driveways, artificial turf and multi-lanes, carpentry, harped topsoil). From a resource reuse perspective, their crushing of concrete and sale of recycled materials are especially relevant. The company purchased a crushing plant in 2004 for crushing concrete rubble and tiles, in order to reduce the use of raw materials such as bottom protection and stable gravel.

Aside from those actors in the basic construction part, there are several companies related to installation services, such as the installation of plumbing, heating, joineries, and roofing.

John Jensen A/S, VVS Installationer was established in 1962 and employs around 200 people today. With their main work revolving around plumbing work, John Jensen VVS A/S services public and private organisations, pharmaceutical and food industry, business and production companies, district heating and housing companies John Jensen A/S 2021.

SH Installation A/S is another plumbing installation company, based in Hedehusene. It has 69 employees and handles different services from single installations to turnkey contracts in plumbing for heat, water and sanitation.

Wicotec Kirkebjerg A/S, though headquartered in Copenhagen, has regional offices in Taastrup with 400 employees. It offers a broad spectrum of services: Electrical and mechanical Services, piping and plumbing services, HVAC services, district heating, fire and protection, building automation, and service & maintenance across numerous industries such as ​​hospitals, pharmaceuticals, education & research, energy supply and district heating, infrastructure, and commercial- and Residential Buildings.

As for joinery installation, Deko P/S is a big employer with 214 employees. The company works on the design, production and ​​installation of partitions of glass, wood, and aluminium. However, it seems that the production site is not actually in Taastrup, but that the location serves as office and storage facility.

Finally, there is one main actor connected to “roofing activities”, namely NimTag ApS. The company, having 30 years of experience, has 40-50 employees, a number of subcontractors and handles various roof tasks such as roofing felt, roof insulation, membrane laying, service inspection and the establishment of green roofs, just as the installation of skylights and fire ventilation NImTag ApS 2021.

Aside from the listed and described companies that engage in the use of construction materials, there are certainly a great many more of them in the municipality. However, for this report, only the main players, those with the largest employee numbers, were included.

Waste collection and treatment

The waste collection and treatment in Høje-Taastrup is generally organised by the municipality itself, which takes care of waste collection for private households, but neither for companies nor demolition waste. For the purpose of the SCA only demolition waste was relevant, which is handled by private haulers. The private haulers need to be officially registered, but it is not the municipality that handles this, but a national system. And the waste depots and recycling drop-off centres are run by private companies, some of which are owned by groups of municipalities. In the construction and demolition waste, the following needs to be separated: natural stone (granite, flint); unglazed bricks and roof tiles; concrete; mixtures of the aforementioned materials; iron and metal; gypsum; fiberglass insulation; soil; asphalt; mixtures of concrete and asphalt. Glass and wood are typically also separated. Waste treatment takes place in the one major waste treatment facility in Høje-Taastrup, the incineration plant. Otherwise the waste is treated in regional facilities, or in only very rare circumstances is it exported.

Data source

As for the waste actors, two main ones with three facilities exist, as can be seen on the map just above. Dansk Miljøforbedring and Vestforbrænding are both waste collection facilities. Dansk Miljøforbedring primarily handles construction waste from large construction projects. The recycling station (Genbrugsstationen) is operated by Høje-Taastrup municipality in collaboration with I / S Vestforbrænding and is geared towards local inhabitants, businesses and smaller constructors doing minor renovations. (Companies can deliver a maximum of 200 kg per year.) At the Vestforbrænding site, 30 different types of waste are collected for recycling and some waste also gets incinerated. Smaller amounts can more easily be collected there. For example, citizens can dispose of up to ten roofing sheets without declaring it at www.bygningsaffald.dk, the national notification form for construction waste. (It should be noted that this website is an optional portal for notification of construction and demolition waste, operated by a consultancy company. There are other systems for notifications of construction and demolition waste, but Høje-Taastrup employs that one.)

Indicators

To monitor the progress of this economic sector towards circularity, a number of indicators were proposed and measured. Altogether, these indicators depict several facets of circularity of the sector. As such, they need to be considered in combination rather than in isolation when assessing circularity. In addition, these indicators can be compared to other cities or spatial scales (such as the country level). However, this has to be done with great care and use of the contextual elements in the previous sections of the report. Finally, the value measured from these indicators can be traced over time to track the sector’s progress towards circularity.

The domestic material consumption (DMC) is calculated by adding “Domestic extraction used” to “Imports” and subtracting “Exports”. For Høje-Taastrup, it amounts to 338,309.13 tonnes and 6.67 tonnes per capita. This value is very low compared to the total DMC of ​​13.4 tonnes per capita for EU-28 in 2019 and even lower relative to the 24.98 tonnes per capita in all of Denmark. However, those latter two also do take into account the total DMC and not just the materials used in the construction sector. Since it goes beyond the scope of this work to determine the share of construction materials in the total economy, it will not be further assessed. It does seem unrealistic that the DMC of Høje-Taastrup is only about a quarter of the national value, as construction materials do usually take up more of the DMC than that. This distorted value could likely origin from the estimation of the export values.

The CMU value of indicator 39 is extremely high with 52%, compared to the 12.4% for EU-28 in 2019 and 7.6% for Denmark. This could be due to the very high domestic recovery value (385,208.04 tonnes), relative to that of extraction (583,198.75 tonnes). The first value, in this case, actually only represents the materials that were subjected to recycling and not of how much was actually recovered. This value was in turn used as a recovery value, as the actual amount that was recovered from recycling is unknown. Another difficulty that is added to this indicator is that it was originally designed for metals. Since now materials from different categories are bundled up, it skews the image of the circularity of materials.

The EU self-sufficiency for raw materials indicator is very low with 1.26%. Unfortunately, there is no national value to compare it to. And since the data completeness was lacking in terms of differentiation of the single materials, this indicator couldn’t be calculated for them individually to determine the various self-sufficiency levels.

The EOL recycling and processing rates are still considerably low with about 15% and 23% respectively. While 19% of materials are still subjected to disposal and 81% to recovery, the efficiency of recovery could still be improved. There is however uncertainty in those values, as the amounts derived from recycling had to be estimated.

The incineration rate is very low with less than 1%. This is somehow surprising, on the one hand as Høje-Taastrup has its own incineration plant. On the other hand, construction waste materials are usually not subjected to a large extent to those facilities.

Finally, the landfilling rate is still quite high at 19%. The numbers came from the waste statistics and can be considered reliable, thus there is no uncertainty there. Either the municipality really still landfills quite a lot of waste, or the values are influenced by a lack of classification or differentiation of waste use on landfills as “alternative daily cover”.

Visualisations

Measuring circularity is a data heavy exercise. Numerous datasets were collected and visualised throughout the sector-wide circularity assessment process. To synthesise these findings, a Sankey diagram illustrates how material flows from the studied economic sector are circulating from one lifecycle stage to another. The height of each line is proportional to the weight of the flow. This diagram therefore helps to quickly have an overview of all the materials flows that compose the sector and their respective shares. The flows that are coloured in light blue in the Sankey diagram, are return flows. This means that they flow in the opposite direction of the lifecycle stages and are subjected to reuse, redistribution, or remanufacturing. Their size relative to the others is a good indication for the materials' circularity.

The Sankey diagram builds of course on the collected data that also the indicators have been derived from. Therefore, it needs to be taken into account that the previously discussed data quality influences also the quality and informative value of the Sankey diagram. In addition to the data quality, so-called allocation values also have an impact on the data behind the visualisation. These allocation values were employed to estimate the amounts of materials that “flow” between the single lifecycle stages, since these relationships and quantities were in most cases unknown, except for waste collection going to waste treatment.

Overall, the Sankey diagram for Høje-Taastrup shows that quite a lot of materials are moving around in the construction sector system. The share for extraction is quite significant. The total amount sums up the four material groups that are extracted in the municipality:

• Lime and chalk
• Clay
• Sand, gravel and stone
• Raw soil and filling area

It can also be seen that a lot of the extracted materials get exported to retail outside of the municipality.

The graph just below shows that the amounts of sand, gravel and stone are clearly and consistently making up the larger shares of all excavated materials. Of the two companies engaging in the extraction activities, NCC Industry A/S dominates with over 90% of the total sand, gravel and stone in each year. Their contribution will decrease tremendously, if not amount to zero, in the next few years, since the gravel pit has been exploited and the company closed down their extraction activities in the beginning of 2021.

Data source

It should be noted that although soil can also be extracted and some data on soil was available from an inventory that registers that transported amounts, it was excluded from the Sankey diagram. This is because it is unknown where the different kinds of soil come from, literally and with respect to the stage in the supply chain and what happens to them. For example, they could be stored, recycled, or undergo a remediation process. For completeness, the amounts are nevertheless depicted in the chart below.;

Data source

As for import and export, while smaller than extraction, they are both fairly similar in size. Manufacturing sees a large inflow of materials from recycling and retail is fed with new materials from extraction, import and manufacturing, as well as secondary materials from incineration and use. This latter return flow from use back to retail could be surplus materials from construction sites that are labelled for reuse.

Going forward in the diagram from left to right, it can be seen that there is a data gap from the outgoing materials from retail to all other lifecycle stages. This reflects on the gap in the data availability described above.

Use is being fed by imported and extracted materials, although the majority would likely origin from retail. Most of the materials from use end up in stock, as constructed materials. Although it seems that most of stock goes to waste collection and a little bit gets reused, this is only true in terms of the data of flows. It might seem that all buildings and infrastructure get demolished again, but this of course isn’t the case. It is just that the Sankey diagram does not depict the stocks, the materials that stay in a system for over a year, but only the flows from the single stages.

While the waste collection node does receive most materials from the stock, it also gets inflows from imports, manufacturing and use. The diagram shows that the main share of materials leaves to recycling, which is also fed by imports and which has a large outflow as return flow to manufacturing. As for the other waste treatment options, landfill is quite high and very similar in size to storage of materials for recycling. Finally, a significant stream is from export to retail abroad.

Data quality assessment

Numerous datasets were collected and considered in the sector-wide circularity assessment. In some cases, datasets were not available for some materials or for some lifecycle stages for the studied sector. Therefore, estimations need to be done by looking at data at higher spatial scales (region or country). This section qualitatively assesses how reliable the data used is.

Data quality

Before describing data gaps and assumptions, the overall data quality is considered. It is expressed through four data quality dimensions that are depicted in the data quality matrix: reliability, completeness, temporal correlation, and spatial correlation. Each dimension has its own criteria for the ranking of high (green), medium (yellow) and low (red), which is based on this Pedigree report and shown in the table below. There can be additional explanations in some cells, as supporting information.

Data analysis

This section analyses the Sankey diagram developed in the previous section. It discusses and interprets the results for the sector-wide circularity assessment. It also reflects on how the current demonstration actions fit within the bigger picture of the sector, as well as how they could be upscaled to accelerate the transition towards a more circular sector.

References

• Denmark
• Hovedstaden
• Københavns omegn
• Population of Høje-Taastrup, 2011-2020 line graph
• Static land use map of Høje-Taastrup
• Geo localisation of extraction companies in Høje-Taastrup
• Header image: Mariusz Paździora, CC BY-SA 3.0, via Wikimedia Commons