Mass timber embodied carbon factors

Arup has conducted a review of European manufacturers’ CLT and glulam Environmental Product Declarations (EPDs). The review demonstrates that the currently adopted industry average carbon factors for CLT and glulam have reduced when compared with factors from the Inventory of Carbon and Energy database (ICE database).

The currently adopted factors are 0.437 kgCO₂e/kg for CLT and 0.512 kgCO₂e/kg for glulam, and are referenced by the IStructE's How to calculate embodied carbon guide¹ for mass timber. The new figures recommended are 0.25 kgCO₂e/kg and 0.28 kgCO₂e/kg for CLT and glulam respectively. This is predominantly due to changes in the recorded energy mix and energy use during production.

This article proposes updating the figures referenced by the IStructE to those based on current European manufacturer EPDs.

The ICE database mass timber carbon factors referenced by the IStructE in How to calculate embodied carbon, are based on a range of international EPDs in addition to data provided by Wood for Good² nearly a decade ago. Given UK consumption of mass timber broadly reflects the distribution of its manufacture across Europe, Arup decided to conduct a review of current European manufacturer EPDs, to derive suitable, up-to-date factors for CLT and glulam.

A1 – A3 embodied carbon factors were extracted from eleven CLT manufacturer EPDs and eight glulam manufacturer EPDs. Manufacturer data was included and weighted based on production volumes, reflecting the likelihood of a particular product being supplied and limiting the skewing of data by EPDs representing a smaller portion of the market.

The EPDs utilised in this work are third-party independently verified, and have been undertaken in alignment with the requirements of ISO 14025 and EN 15804.

Figures 1 and 2 show current European production volumes from CLT and glulam manufacturers respectively³.
Figures 3 and 4 show the distribution of A1 – A3 embodied carbon factors (excluding sequestration) for CLT and glulam⁴, as well as the derived weighted average figure calculated by Arup. Average A1 – A3 embodied carbon factors, weighted by production, are 0.25 kgCO₂e/kg and 0.28 kgCO₂e/kg for CLT and glulam respectively.

"These new carbon factors for CLT and glulam represent an important progression of the knowledge base. It’s encouraging to see that many of the main CLT and glulam manufacturers have published Environmental Product Declarations (EPDS), which provides the embodied carbon of their products. This new research shows the benefit of more suppliers publishing the embodied carbon of their products, giving a welcome reduction in the embodied carbon of CLT and glulam."

Dr Craig Jones, Circular Ecology

Figures 5 and 6 below show the mixture of renewable and non-renewable primary energy quoted by each manufacturer (including renewable energy from burning waste wood on-site). The ICE database does not provide an energy breakdown with its carbon factors. However, the Wood for Good (2013) EPDs, which formed part of the ICE database study and represented a 2013 UK industry average, has been used to give an indicative energy mix for the study period. Several observations can be made:

Less energy is typically used by each manufacturer to produce 1m³ of mass timber compared to the Wood for Good analysis
Less non-renewable energy is typically used by each manufacturer to produce 1m³ of mass timber compared to the Wood for Good analysis
The A1-A3 embodied carbon factors correlate to the non-renewable energy component quoted by each manufacturer

Based on industry engagement, primary contributing factors also include varying transport distances during production, the energy mix of the country of manufacture and the utilisation of the factories studied.

It is also useful to compare the new embodied carbon factors derived to the value for conventional sawn and dried softwood timber.

The softwood value given in the ICE database and the IStructE guide is 0.263 kgCO₂e/kg – very similar to the new values for CLT and glulam proposed. A review of current EPD data from Europe’s largest sawn and dried softwood timber producers suggests that this value may also warrant reduction, and further work by the industry in this space is suggested.

Conclusion

It was found that current European mass timber EPDs give lower carbon values than those derived previously by the ICE database. The EPD data utilised in this study is more recent than data utilised for the existing carbon factors and covers approximately 85% of the volume of CLT and 50% of the volume of glulam produced in Europe. Our recommendation is that new weighted average values are adopted for CLT and glulam structures being constructed across Europe, including in the UK.

In addition, the following further work is proposed:

Development of up-to-date embodied carbon factors for European sawn and dried softwood, hardwood, plywood, oriented strand board and laminated veneer lumber
Development of timber factors for other global regions
Refinement of assumptions around transport routes via road and sea, to capture the increasing influence of stage A4 as earlier production stage factors reduce
Further review of lifecycle stages B – D to understand the current whole lifecycle carbon factors for mass timber products

The authors of How to calculate embodied carbon have confirmed that these figures will be included in the next revision of the guide, due for publication in Spring 2022.

References

[1] The Institution of Structural Engineers (2020). How to calculate embodied carbon

[2] Jones, C. and Hammon, G. (2019). ICE (Inventory of Carbon & Energy) Database Version 3.0. Circular Ecology and University of Bath. Available at: https://circularecology.com/embodied-carbon-footprint-database.html

[3] Production Volumes
Construction.co.uk. Moelven Laminated Timber Structures
Holzkurier. Expresslieferung in den Norden
Rubner Holzbau. Our strategy. Wood experts
Setra. Långshyttan - Setra's new wood industry hub
Splitkon. Massivtre fra Splitkon
Timber Online. Eight new CLT production sites by 2023
Timber Online. Over 3 million m³ for the first time – record years for glulam
Timber Online. The biggest CLT producers in Central Europe
Versowood. Puureferenssit. References

[4] Environmental Product Declarations
CLT EPDs: EPD-BBS-20190021-IBB1-EN, EPDHAS20210172IBD1EN, EPD-KLH-20190027-ICA1-EN, EPD-SHL-20180035-IBG1-EN, EPD-SLH-20200098-IBC1-DE, NEPD-2042-902-NO, S-P-01408, S-P-02033.
Glulam EPDs: EPD-BBS-20190164-IBA1-EN, EPDHAS20210171IBD1EN, EPD-RUB-20180058-IBB1-EN, EPD-SHL-20120017-IBG1-EN, NEPD-1662-655-EN, NEPD-456-318-EN.

Wood for Good life cycle assessments
Wood for Good. Glued Laminated Timber
Wood for Good. Cross Laminated Timber
Manufacturers were contacted directly where production volumes and/or EPDs were unavailable online. All references accessed November 2021.

[5] Codes and Standards
BS EN ISO 14025:2010 Environmental labels and declarations – Type III environmental declarations – Principles and procedures London: BSI, 2010
BS EN 15804:2019 Sustainability of construction works. Environmental product declarations. Core rules for the product category of construction products. London: BSI, 2019.