Keywords

1 Introduction

Embodied emissions will likely constitute the majority of emissions generated by new buildings built between now and 2050 (Simonen et al. 2017). It is increasingly recognised that embodied impacts can constitute more than half of the total life cycle impacts from new buildings, and they will grow both proportionally and in real terms with the reduction of operational impacts (Rasmussen et al. 2018). ‘Net-zero’ or ‘near-zero’ operational greenhouse gases (GHG) emissions mean that the GHG emissions budget becomes almost entirely allocated for embodied GHG emissions (Röck et al. 2020; Habert et al. 2020; Moncaster et al. 2019).

Current EU regulations mainly cover the operational energy performance of buildings, while the embodied impacts remain largely unregulated, despite the significant carbon reduction potential (Toth and Volt 2021). However, since 2017, the Netherlands has required all new residential and office buildings larger than 1000 m2 to account for embodied impacts based on a simplified LCA. Switzerland has introduced LCA requirements for public buildings (Swiss Society of Engineers and Architects (SIA) 2017). Denmark’s National Strategy for Sustainable Construction will phase a LCA requirement into the building code, enforcing maximum CO2 emissions of new buildings larger than 1000 m2 from 2023 and for all new buildings from 2025 (The Danish Housing and Planning Authority 2021).

France’s new Réglementation environnementale RE2020 includes carbon thresholds for offices and educational buildings starting 1 July 2022; limits will be progressively lowered. France is the first country to apply a dynamic LCA approach to the construction sector (Ministère de la Transition écologique (MTE) 2022a; Ministère de la Transition écologique (MTE) 2022b).

These increasing efforts for setting legally binding limits to the embodied environmental impacts highlight the crucial need for developing accurate, equitable, and easily accessed data for construction materials and techniques.

2 Data and Methods

2.1 Case Studies

The reflections proposed in this paper stem from the analysis of twenty-two ecologically oriented buildings showing different approaches to ‘vegetarian architecture’—a theoretical stance based on principles learnt from agriculture and nutrition (Bocco Guarneri 2020), which advocates:

  • natural, renewable, locally available construction materials, free of toxic chemicals, and as little processed as possible (Wolley 2017, 2016; Berge 2009; Ghavami 2014; Walker et al. 2009; Harries and Sharma 2016);

  • minimization of energy-intensive, high-tech components;

  • labour-intensive, small-scale production processes, and simple constructional techniques;

  • passive solar design.

The case studies are located in Europe and Japan and cover a variety of functions—residential, commercial, educational, workspace—and different patterns of use. Their gross internal areas (GIA) range from 23 to 3 232 m2. Both refurbishment of traditional buildings and new constructions are included to exemplify techniques that make use of bio-based and other natural materials.

2.2 Data

The systematic investigation of each building’s technical and constructional features allowed to draw inventories and 3D models representing as-built situations. The ‘cradle to gate’ embodied energy (EE) and ‘embodied carbon’ (EC) were calculated by adding up the components manually, using a process-based LCA methodology and a purpose-designed spreadsheet. Impact coefficients were retrieved from two open access databases—the Inventory of Carbon and Energy (ICE) (Jones and Hammond 2019; Hammond and Jones 2011) and Ökobaudat (ÖBD) (BMI 2021).

Later, the most relevant non-conventional materials (NOCMAT) used were identified. NOCMAT encapsulate sustainable use of novel technologies and innovative uses of more established materials; many of them have their roots in traditional vernacular construction, including bio-based materials, and other natural materials such as stone, earth, lime (Ghavami 2014). For these materials, EE and EC values are either unavailable or show inconsistencies in the databases used. The production processes and the uses of such materials show a wide variability, which leads to a variability of the associated environmental impacts.

2.3 Reference Databases

ICE and ÖBD were chosen because open access and user friendly. More detailed sources are available but are proprietary and/or require a high level of expertise for their use. Using ÖBD and ICE to calculate the two basic environmental indicators was a sensible compromise between data availability and results uncertainty. Using the same set of values for all calculations guaranteed consistency.

ÖBD is managed by the German Federal Ministry of the Interior, Building, and Community; datasets must comply with EN 15,804. Data entries are constantly added, and the entire database is updated once a year. Datasets are based on the background database GaBi. Additional datasets based on EcoInvent background data are provided. In 2020, the new DIN EN 15,804 + A2 was adopted, which includes separate reporting of fossil, biogenic, and luluc GWP.

ICE is managed by Circular Ecology and the University of Bath. Version 2.0 (2011) was based on ISO 1404 and 14,044; 53% of sources dated before 2005. Carbon sequestration was excluded. Version 3.0 (2019) no longer includes energy factors. Carbon storage data are available for timber only. The values are the average of several sources, usually EPDs complying with EN 15,804. Data are updated for some materials. In our study, ICE V2.0 was used for all EE values and some EC values.

3 Results

3.1 On Case Studies’ Embodied Energy and Embodied Carbon Values

While a rigorous internal methodology allowed for a detailed comparison between case studies (Bocco and Bocci 2022), it was difficult to verify whether these buildings have a lower environmental impact than conventional ones (Bocco Guarneri 2020). Systematic reviews (Simonen et al. 2017; Rasmussen et al. 2018; Birgisdottir et al. 2017; Dixit 2017; Hoxha et al. 2017; Röck et al. 2019; Säynäjoki et al. 2017; Schwartz et al. 2018) have not yet reached the degree of harmonisation which would offer benchmarks. The completeness of the underlying inventories is doubtful; the variations are up to two orders of magnitude (Rasmussen et al. 2018).

The average results of the analysed ‘vegetarian’ buildings do not appear significantly lower than those found of more conventional buildings. Moncaster et al. (Moncaster et al. 2019) found an average of 125 kgCO2eq/m2 for retrofitted buildings and of 254 kgCO2eq/m2 for new ones; we obtained 127 and 328, respectively, with ICE, and −132 and −74 with ÖBD (Fig. 33.1). The question about the reliability of databases, methodologies, and benchmarks stays open.

Fig. 33.1
A table of 7 columns and 19 rows gives details of G I A, weight, and the O B D and I C E values of E E and G W P, for building numbers 1 to 14, 1 r to 3 r, and the average. The entries include 114-meter square G I A, and 381 megajoules per meter square for G I A and O B D values of E E, in order.

GIA, weight, EE, and GWP of each case study, calculated both with ÖBD and ICE

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3.2 On Vegetal Materials

The analysis highlighted a divergence of the profiles for timber and timber-based products in the two databases. Data for highly industrialised products such as timber-based boards and window frames are widely available and cover a good range of variations; this comes less for untreated solid wood. ÖBD provides very high values for EE, reflecting German processing: kiln drying; industrial debarking and sawing machinery; and an average distance between forest and sawmill of 144 km (Fig. 33.2). While timber was widely used in most of our case studies, it was often low processed and underwent little treatment, if any. In most cases, timber was air-dried, while most sources for both databases consider kiln drying at high temperatures—an energy—and carbon-intensive process that alters timber’s properties. Where elements were hand-sawn (5), debarked and cut on site (21), and untreated (5, 6, 21), the impact risked to be overestimated (Fig. 33.3). In case 21, the whole structure—which makes a relevant portion of the building’s weight—was manually debarked, and most of the lumber came from the site or district forest. In 5, timber was obtained from the ecovillage’s forest and transported with horses to the site, where it was assembled with hand tools. No data are available for brettstapel (7, 13, 17, 22) as opposed to various entries for laminated timber: the lack of glue and nails reduces the environmental impacts of the first. Wood chips (21) and loose wood fibre (10) are not covered, as opposed to wood fibre boards for which ÖBD includes five entries and ICE two.

Fig. 33.2
A photograph of dried timber stacked on shelves. A circle-shaped moist area sits in the center of many medium-sized squares on the front side.

Timber dried at low temperatures in a greenhouse at Kitokuras sawmill (Kagawa prefecture). Photo Andrea Bocco Guarneri

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Fig. 33.3
A man debarks a felled tree trunk with a log peeler spud in this photo.

Manual debarking of trees at Biotal site. Untreated logs are used as structural columns in the building. Photo Christoph Bosch

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Straw was employed in ten case studies in a range of ways: load-bearing bales (6, 7, 21), thatch (2), bale infill (12, 20), bale retrofit (3), loose insulation (1, 6, 15, 21); ropes, mats (1), and chaff (2) are also used. Only values for standard size bales with a density of 100 kg/m3 are given in the databases, forcing an approximation for products like jumbo and round bales and loose straw. Not only does the crop cultivation vary (in 5 and 21 it is harvested from local organic farms), but also the baling process is expected to influence the overall impact. In many of these buildings, straw represents a large portion of the weight: divergences can therefore influence the overall environmental impacts. Reported values for straw bales are disorienting: in ÖBD, the EE value for straw (17.13 MJ/kg) is seventy times higher than that found in ICE 2.0, and higher than that of structural steel (14.14 MJ/kg) and more than three times higher than that of fired, solid bricks (4.85 MJ/kg). The reliability of the EE value for straw in ICE may be low, since it is based on four references only, the latest dating from 2003; but that in ÖBD (based on an EPD provided by FASBA) is high compared to recent studies: e.g., nearly 5 times higher than Upstraw School of Natural Building’s 2021 EPD (Up-Straw—School of Natural Building (SnaB) 2021).

Databases seem also ill-suited for representing other vegetal materials. No data are present in either database for bamboo, not only for whole culms but also for products such as mats, panels, and laminated bamboo. In 9, locally harvested bamboo culms make up the entire structure (Fig. 33.4). Loose hemp shiv is not covered, which makes it difficult to assess, for instance, hemp-lime building components (8, 13). Only hemp mats are found in ÖBD (Fig. 33.5): these include 15% polyester fibres and are impregnated with soda.

Fig. 33.4
A close-up of a series of vertically, radially, and horizontally assembled bamboo sticks tied together tightly with strings.

Structure of the Bamboo Ark consists of radially arranged frames, composed of a base truss and arches. The culms were harvested from a nearby grove. Photo Toki Hirokazu

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Fig. 33.5
A photo of a reed mat with plaited reeds and weft-faced weaves.

Bamboo mats in Iya Valley, Japan. Photo Andrea Bocco Guarneri

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Analogously, there are no data for loose flax fibres (21), just for mats. In ÖBD, the same assumptions as for hemp fibre mats are applied. ICE V2.0 reports that most of the impacts are due to the polyester binders and fire retardants (Schmidt et al. 2004). No data are present in either database for reed mats (4, 6) and jute (6), while building paper (10, 13) is covered by ÖBD only.

3.3 On Other Natural Materials

Earth construction techniques are poorly represented: ICE just reports data on earth (it is unclear whether this is rammed or bulk earth); ÖBD includes data on rammed earth, adobe, plaster, earth panels, and bulk earth. Data sheets do not provide enough information on basic features, such as the presence of additives or fibres, or the size of the adobes. The entry for earth plaster in ÖBD has an ambiguous description, which does not even seem to refer to an earth-based product. ÖBD also assumes processes such as the artificial drying of adobes (Fig. 33.6).

Fig. 33.6
A photo indicates an oblique outlook of a house's wall with a batten. One-half is thatched with a light-earth skin.

Light-earth external skin applied onto battens in a new house in Darmstadt. Photo Franz Volhard

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No data are provided for earth paints, which are usually ready-made products (4, 8).

In many case studies, earth products were made at the construction site (Fig. 33.7): adobes in 10 and 12; manually compressed earth blocks in 13; earth plasters in 2, 5, 6, 10, 12, and 21 made with various mixtures, in some cases including fibres, sand, or lime; clay mortar in 4; tamped earth floors in 1, 4, 5, 6, 12, and 14 (coated with earth finishing in 6 and 12). Earth was also used with straw for infilling wooden or bamboo frames (1,2,4,15,21).

Fig. 33.7
A photo of a construction worker engaged in work with all safety equipment near a narrow pillar. Several such pillars arise from a long and sturdy platform beneath.

Construction of the lecture theatre of the WISE at the Centre for Alternative Technology. The attractive load-bearing rammed-earth walls, 500 mm thick, are pneumatically tamped and left unfinished on both faces. Photo Pat Borer

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Emblematic is the case of stone: while being one of the most common materials in vernacular constructions, its use has drastically shifted from massive blocks that require minimal (if any) dressing to 1 ~ 3-cm-thick cladding slats. Both databases just provide values for thin elements that underwent cutting and finishing processes. In ÖBD, entries for 2 ~ 4-cm-thick granite and limestone elements assume processing—steel grit, grinding road, saw, and multi-blade saw. ICE V2.0 acknowledges that data sources were generally poor, except for stone slates. Quarried stone blocks are then associated with a risk of overestimating their embodied impacts if the custom values are employed. Even in cases when thin paving stone slabs were used, ecological considerations resulted in specifying little-processed elements: in 7, 50 ~ 70-mm-thick soapstone flooring slabs were obtained on site by cutting conglomerate rock boulders; in 21, 9-mm natural stone tiles were hand-cut with pliers and left unpolished.

Animal-origin products are also little represented, if at all: for felt (7), the only data available is the EE value in ICE V2.0; for sheep’s wool (8, 18), no values are available in either database.

4 Conclusions

The quality of the environmental assessment of buildings depends heavily on the quality of the data used, which remains a major challenge. Most of the processes mentioned here could be modelled with tools such as EcoInvent: but doing so requires skills and time that are beyond the possibilities of an average designer or contractor. ÖBD and ICE, while open source and easy to use, are focused on conventional materials and do not satisfactorily cover bio-based and little-processed materials. Even when they do, the values provided are regional or global averages, not representative of specific production patterns in terms of processes or efficiency, electricity mix, and transportation distance (Zea Escamilla and Habert 2014).

A proper assessment requires significant expertise, time, and financial resources, which are less likely available for alternative construction materials. Furthermore, meeting the impact thresholds set by current and future regulations pushes towards using certified conventional construction materials, a tendency that is not consistent with decarbonizing the building trade. Data availability is then a key issue in the implementation of environmental reduction policies.

The development of appropriate data for non-conventional construction materials should be supported by a bidirectional technological transfer between the research and industry sides. Current research efforts should be aligned to make the results reliable and widely available. This will rebound on an easier introduction of these materials in the construction market and help achieve the ambitious emissions reduction targets.