Grantham Institute - Climate Change and Environment at Imperial College London              SBE0059

Written evidence submission from the Grantham Institute – Climate Change and Environment at Imperial College London

About the Grantham Institute – Climate Change and the Environment at Imperial College London

The Grantham Institute is committed to driving research on climate change and the environment, and translating it into real world impact. Established in February 2007 with a £12.8 million donation over ten years from the Grantham Foundation for the Protection of the Environment, the Institute’s researchers are developing both the fundamental scientific understanding of climate and environmental change, and the mitigation and adaptation responses to it. The research, policy and outreach work that the Institute carries out is based on, and backed up by, the world-leading research by academic staff at Imperial.

 The evidence submission has been prepared by the following authors:

Summary

This submission focuses primarily on the role materials can play in driving a shift to low-carbon buildings. Specifically, the submission highlights:

How can materials be employed to reduce the carbon impact of new buildings, including efficient heating and cooling, and which materials are most effective at reducing embodied carbon?

1. More than 60% of the life cycle greenhouse gas emissions from newly constructed, modern buildings (assuming a 60 year life cycle, with increasing grid decarbonisation to 100% over this time scale) come from their embodied emissions.[1] ‘Embodied emissions’ are here defined as the activities required for a building to exist, such as materials production, construction and demolition, but excluding its operation. Most of these embodied emissions are from materials production, in particular from the production of structural materials like steel, concrete, and wood. Whether the 60-year lifespan commonly used for assessing buildings is adequate, warrants consideration.

2. Fewer materials should be used in the construction of new buildings to reduce their carbon impact. This can be achieved by reducing demand, for example through more efficient/creative design, but can also be achieved through improved material performance. Here, an important measure to reduce demand is ‘sufficiency’, meaning using just enough products/services (and thus resources) to satisfy basic needs, avoiding excessive consumption. A key example of this is a ‘tiny house’, which provides the basic need for shelter but avoids excessive consumption of floor space. Therefore, building ‘tiny houses’ rather than standard sized houses has a high potential to reduce carbon emissions (see ‘more intensive use’ here).[2] 

3. The most effective materials to reduce embodied carbon are lower carbon structural materials. Structural materials include concrete, steel, and timber, and they are used in building frames to support loads. For concrete, it is important to reduce Portland cement clinker content, which is the reactive material in cement that makes it set, and which is very carbon intensive to produce due to its inherent chemistry and high processing temperature.

4. An excellent example of how to deliver such reduction is through using calcined clay to substitute Portland cement clinker in cement[3], although this may only marginally reduce greenhouse gas emissions relative to current blast furnace slag-coal fly ash blended cement due to their comparable levels of Portland cement clinker.[4] A main benefit of switching materials use to calcined clay cement is more reliable material supply, as clays are abundant but coal fly ash is declining in the UK. 

5. Steel should be produced with as high recycled content, and thus the lowest virgin material content, as possible to reduce embodied carbon in buildings where it is used. Wood can generally be considered a low-carbon material, but its use does have significant environmental impacts and is not always carbon negative. Its carbon emissions are reduced if it is sourced from forests with shorter rotation periods, and if it is used in the built environment for longer periods. Typically, the rotation periods should be less than a century and the wood should be used for decades.[5] As such, the carbon performance of wood depends strongly on forest management and building design/use.

6. Developments in materials arising from new manufacturing developments also mean that a single material no longer needs to be regarded as homogenous. Heterogeneous materials (commonly referred to as multi-functional or hybrid materials, depending on the context) can provide multiple functions with lesser overall resource use. For example, it is possible to manufacture construction materials and products with internal structures that provide a variety of functions such as strength, fluid flow, thermal storage. An example is permeable pavement, which provides drainage and load-bearing capability.[6] The use of structure therefore offers significant potential for transformation. 

7. In addition, the construction of any new building with significant amounts of materials sourced from the materials of existing structures can offer a route to offset the environmental impact associated with the production and transportation of virgin materials. Here, substituting virgin materials with greater amounts of secondary materials generally leads to reductions in carbon emissions.

What role can nature-based materials play in achieving the Government’s net zero ambition?

8. As set out above, structural materials are the main source of embodied emissions. As such, it is essential that emissions from using and producing materials are reduced. Nature-based materials such as biomass can play an important role here. The key biomass structural material is wood, and it is most efficiently used in structures in engineered wood products such as glued laminated timber (known as gluam) or dowel laminated timber (dowellam), the latter of which has a better environmental performance since it does not require carbon intensive glue for its use. 

9. Other nature-based materials exist, for example hempcrete blocks, which are non-load bearing blocks made from hemp plants and a binder (typically lime-based). However, it is doubtful they can be deployed at mass scale as their increased production would require large-scale land-use that is generally in competition with many other (and potentially more resource efficient) uses, such as farming. Straw and other biomass materials can be used for insulation, substituting rockwool.

10. Waste biomass fuels can be used to replace fossil fuels in materials production, but their use for this purpose is limited by their availability. Use of virgin biomass for fuel also does not necessarily reduce life cycle greenhouse gas emissions.[7] Overall, biomass materials can have a beneficial but limited potential to achieve the Government’s Net Zero ambition.

11. Additional supply and biogenic carbon accounting/storage issues, which are key for the use of wood, must also be considered. Wood buildings generally have lower life cycle greenhouse gas emissions than buildings predominantly using other structural materials, so should generally be used where possible. However, as described above, wood is not always a ‘carbon negative’ material. Wood availability is also limited, much more so than raw materials for concrete such as limestone and gravel. It is produced in much lower quantities than concrete (about 30 times less globally, ~42 Gt vs. ~1.2 Gt[8], and its production would need to be greatly expanded to substitute concrete fully. This is unlikely to be achieved at pace, carries major implications for land-use, and may not be possible at all in some regions, such as those lacking suitable forests.

What methods account for embodied carbon in buildings and how can this be consistently applied across the sector?

12. Life cycle assessment is the best and most appropriate method to account for embodied carbon. A strength of the approach is that it can be performed in a streamlined (i.e. relatively simple) manner as well as more comprehensively, and that the more streamlined approach can also lead to reliable and insightful results and conclusions. 

13. The sector should consistently follow/use the ISO standards literature on life cycle assessment (ISO 14040[9], ISO 14044[10]) and the more specific British Standard (BS EN 15978:2011[11]) which applies life cycle assessment specifically to buildings. The ISO standards require results of life cycle assessment studies to be independently verified by an expert if comparative assertions are intended to be made to the public. 

14. The EU Product Environmental Footprint approach was developed with the intention to enable life cycle assessment studies to be done on a comparable basis[12], however it is considered by some to be inherently flawed since it imposes prescribed conditions on the studies that are prone to manipulation and may not be scientifically robust.[13] A solution to these issues can be to maintain strict rules and regulations around misleading claims about environmental performance, that also requires the data underpinning the studies to be published so this can be transparently scrutinised. Open publication and scrutiny of results is important in order to achieve consistency across the sector, as it will generally improve practice and facilitate learning.

Should the embodied carbon impact of alternative building materials take into account the carbon cost of manufacture and delivery to site, enabling customers to assess the relative impact of imported versus domestically sourced materials?

15. Yes, absolutely. All Scope 1, 2, and 3 emissions should be included in determinations of the carbon emissions of products, otherwise the assessments are likely to lead to misleading results and interpretations.

16. However, it is important to emphasise that transport is responsible for less than 5% of life cycle greenhouse gas emissions for concrete.[14] Transport emissions also only play a minor role for most other building materials.[15] By far the majority of greenhouse gas emissions are from materials production, and it is these emissions that must be reduced. Focusing on transport emissions risks distracting from the more important measures to reduce embodied carbon, such as substituting Portland cement clinker, the role of sufficiency, using wood as a building material, off-site construction etc.

How well is green infrastructure being incorporated into building design and developments to achieve climate resilience and other benefits?

17. Although green infrastructure (GI) is widely recognised as a way to provide multiple benefits for the built environment, there is still a lack of wide uptake of GI interventions.[16] To be used effectively, GI must be analysed at a range of urban scales using the principles of a systems approach to urban planning.[17],[18]

18. At local and development scales, GI can be designed to protect critical infrastructure[19] and provide a range of ecosystem services through blue-green urban design.[20] At a city scale, GI should be considered in an integrated way together with other building and water infrastructure solutions to provide benefits for both managing urban flood risk[21] and reducing environmental impacts such as in-river water pollution.[22] 

How should we take into account the use of materials to minimise carbon footprint, such as use of water harvesting from the roof, grey water circulation, porous surfaces for hardstanding, energy generation systems such as solar panels?

19. Materials that reduce carbon footprint do not necessarily reduce energy or water use or lead to environmental benefits in other areas. These are different environmental issues and need to be considered as such. A ‘materials selection’ approach can be used to assess the environmental performance of whole buildings, and then assess its subsystems (e.g. structure such as foundations, services such as HVAC, skin such as cladding), which themselves use different technologies (roof water harvesting, grey water circulation, porous surfaces, etc).[23] Different combinations of technologies and subsystems can then be used to design and construct the whole building. The life cycle environmental impacts of whole buildings can be determined in this way.

How should re-use and refurbishment of buildings be balanced with new developments?

20. The UK’s current housing stock includes several standard archetypes, from terraces, semi and detached to low, mid and high-rise flats. These archetypes offer the potential for continued service to society by enabling access to tried and tested accommodation and cultural heritage. However, challenges in the continued use of older housing stock include: perceptions of costs, decision- making to inform selection of appropriate interventions, the perception that ‘to knock it all down and start again’ might be better, and the opportunity to provide return on investment by placing a larger home on an existing plot. 

21. Significant measures are available to enable transformation including: passive-active ventilation; smart thermal management; envelope insulation including floor insulation; and sealing and air management technologies. In the past, the return on investment and lack of access to relevant expertise and technology has resulted in decisions to demolish existing houses and rebuild. However, a series of enabling technologies and new modelling methods are transforming the traditional decision-making process, making refurbishment a viable option.

22. From the perspective of reducing greenhouse gas emissions, buildings should generally always be re-used and refurbished, since this is likely to reduce the demand for new materials production. They should be re-used/refurbished to a high-quality standard, meaning that they are highly energy efficient, durable, and aesthetically attractive. However, if demand for buildings is greater than the amount of buildings that may be re-used or refurbished, then existing buildings need to be repurposed, such as those which are unused or poorly utilised. 

 

23. New buildings may also need to be built to meet demand. In this case, it is essential that new buildings are constructed to a high quality, to achieve a low energy/passive rating (low operational emissions), to make them appear desirable with less floor area in order to reduce material demand and embodied emissions, and ensure they can be used for many decades, extending their service life and further reducing material demand. Architects and designers have a key role to play in ensuring new buildings are made to last. 

 

May 2021


[1]Royal Institute of British Architects. (2017). Embodied and whole life carbon assessment for architects. Available at: https://www.architecture.com/-/media/gathercontent/whole-life-carbon-assessment-for-architects/additional-documents/11241wholelifecarbonguidancev7pdf.pdf

[2] IRP (2020). Resource Efficiency and Climate Change: Material Efficiency Strategies for a Low-Carbon Future. Hertwich, E., Lifset, R., Pauliuk, S., Heeren, N. A report of the International Resource Panel. United Nations Environment Programme, Nairobi, Kenya.

[3] Scrivener, K. et al. (2018). Calcined clay limestone cements (LC3). Cement and Concrete Research 118:49-56 doi.org/10.1016/j.cemconres.2017.08.017

[4] Miller, S. A. and Myers, R. J. (2019). Environmental Impacts of Alternative Cement Binders. Environmental Science & Technolology, 54, 2, 677–686 doi.org/10.1021/acs.est.9b05550

[5] Guest, J. et al (2012). Global Warming Potential of Carbon Dioxide Emissions from Biomass Stored in the Anthroposphere and Used for Bioenergy at End of Life. Journal of Industrial Ecology, 17:1, 20-30 doi.org/10.1111/j.1530-9290.2012.00507.x

[6] Kia, A., Wong, H. S. & Cheeseman, C. R. (2021) High-strength clogging resistant permeable pavement, International Journal of Pavement Engineering, 22:3, 271-282, DOI: 10.1080/10298436.2019.1600693

[7] Searchinger, T. et al. (2008). Use of U.S. Croplands for Biofuels Increases Greenhouse Gases Through Emissions from Land-Use Change. Science Vol. 319, Issue 5867, pp. 1238-1240 DOI: 10.1126/science.1151861

 

[8] Heeren, N. and Myers, R. J. (submitted/under review). Sustainable construction materials. Journal of Physics:Materials

[9] ISO. (2016). ISO 14040:2006. Environmental management — Life cycle assessment — Principles and framework. Available at: https://www.iso.org/standard/37456.html

 

[10] ISO (2016). ISO 14044:2006. Environmental management — Life cycle assessment — Requirements and guidelines. Available at: https://www.iso.org/standard/38498.html

[11] British Standards Institution. (2011). BS EN 15978:2011 Sustainability of construction works. Assessment of environmental performance of buildings. Calculation method. Available at: https://shop.bsigroup.com/ProductDetail?pid=000000000030256638

[12] European Commission. (Accessed 14/5 2021). The Environmental Footprint Pilots. Available at: https://ec.europa.eu/environment/eussd/smgp/ef_pilots.htm

 

[13] Sevenster, M. (2018). PEF weighed and found wanting. 2.-0 LCA consultants. Available at: https://lca-net.com/blog/pef-weighed-and-found-wanting/

[14] Pamenter, S. and Myers, R. J. (2021). Decarbonizing the cementitious materials cycle: A whole‐systems review of measures to decarbonize the cement supply chain in the UK and European contexts. Special Issue: Material Efficiency for Climate Change Mitigation, Volume25, Issue2, 359-376 https://doi.org/10.1111/jiec.13105

[15] Alig M., Frischknecht R., Krebs L., Ramseier L., Stolz P. (2020): LCA of climate friendly construction materials, treeze Ltd., Uster. Commissioned by EnergieSchweiz and Amt für Hochbauten Stadt Zürich. Available at: https://treeze.ch/projects/case-studies/building-and-construction/climat-1

[16] Brown, Kathryn & Mijic, A. (2019). Integrating green and blue spaces into our cities: Making it happen. Grantham Institute, (30), 1-10.

[17] Bozovic, R., Maksimovic, C., Mijic, A., Smith, K. M., Suter, I., & Van Reeuwijk, M. (2017). Blue Green Solutions. A Systems Approach to Sustainable and Cost-Effective Urban Development.

[18] Hattab, M. H. E., Theodoropoulos, G., Rong, X., & Mijic, A. (2020). Applying the systems approach to decompose the SuDS decision-making process for appropriate hydrologic model selection. Water, 12(3), 632.

[19] Ossa-Moreno, J., Smith, K. M., & Mijic, A. (2017). Economic analysis of wider benefits to facilitate SuDS uptake in London, UK. Sustainable Cities and Society, 28, 411-419.

[20] Puchol-Salort, P., O’Keeffe, J., van Reeuwijk, M., & Mijic, A. (2021). An urban planning sustainability framework: Systems approach to blue green urban design. Sustainable Cities and Society, 66, 102677.

[21] Babovic, F. and Mijic, A., 2019. The development of adaptation pathways for the long‐term planning of urban drainage systems. Journal of Flood Risk Management, 12(S2), p.e12538.

[22] Dobson, B., & Mijic, A. (2020). Protecting rivers by integrating supply-wastewater infrastructure planning and coordinating operational decisions. Environmental Research Letters, 15(11), 114025.

[23] Ashby, M. F. (2016). Materials Selection in Mechanical Design. Butterworth-Heinemann