BRE Centre for Innovative Construction Materials, University of Bath              SBE0036


Written evidence from the BRE Centre for Innovative Construction Materials, University of Bath



Submission prepared by: Dr Stephen Allen, Dr Antony Darby, Dr Veronica Ferrandiz-Mas, Dr Will Hawkins, Dr Juliana Calabria-Holley, Dr Daniel Maskell, Matt Roberts, Dr Andrew Shea, Dr Victoria Stephenson, Prof. Pete Walker (Centre Director).



The BRE Centre for Innovative Construction Materials is an independent university research centre at the University of Bath. Working collaboratively with the BRE (Building Research Establishment Ltd) since 2006, it is one of a series of university centres of excellence supported by The BRE Trust.



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?


Materials drive carbon emissions across the life cycle of buildings. The choice of materials influences ‘operational carbon’ (e.g. the choice of insulation materials influence heating and cooling), and dominates ‘embodied carbon’.


The stages often referred to as ‘embodied carbon’ are outlined by the orange box in Figure 1, below. For example, there are emissions during manufacturing and transportation of materials, and during onsite construction processes. Some materials need to be replaced during the life of a building, and this is likely to happen more frequently for less durable materials. There are emissions at the “end of life”, including for waste processing. Some materials have higher waste processing emissions than others, and some are more amenable to reuse, recycling, or energy recovery (accounted for in ‘Module D’). So, for materials to be effective at reducing the carbon impact of new buildings over the long term, they need to be low carbon overall, across all life cycle stages.

Figure 1. Building life cycle stages (Source: Roberts et al 2020).


The question of which materials are most effective at reducing embodied carbon is context dependent. For example, we have found that in case studies we have analysed, timber has been the lowest carbon option as a structural material (Hawkins et al 2021). But the lowest carbon option for insulation, or for different types of structure to the ones we have studied, may be different. That said, general principles for reducing embodied carbon include:



Environmental Product Declarations (EPDs) summarise environmental data for construction materials, including embodied carbon. EPDs are summaries of life cycle assessments that meet European or international standards (such as EN 15804 and ISO 21930). Since 2010 there has been an explosion in EPD availability, with approximately 1,000 published per year. EPDs are thus a valuable data source for selecting low-carbon materials. Recent briefing papers on EPDs are available from the Alliance for Sustainable Building Products. The ICE Database is a popular resource that gives a summary of embodied carbon data from EPDs, but it focuses on material production (Module A1-3) only. It is currently being updated. For further detail on options for reducing embodied carbon of materials, see Giesekam et al. (2014) and Pomponi and Moncaster (2016).



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


Nature-based materials include products derived from bio-based and mineral resources, and broadly encapsulate materials used in their natural state without significant chemical transformations due to heating or other high energy intensive processes (Almenar et al. 2021, Nesshover et al., 2019). Nature-based materials generally have much higher environmental credentials than anthropogenic materials. Founded at the COP21, the GlobalABC (Global Alliance for buildings) have recently published a report:  ‘2020 Global status report for building and construction – Towards a Zero-emissions, efficient and resilient buildings and construction sector' (GSR 2020). This report was endorsed by the UN environment programme, and nature-based solutions have been identified as a focus area towards achieving net-zero buildings.


Examples of natural mineral materials are stone and earth, including rammed earth and cob. The most widely used bio-based natural material is timber, generally derived from plantation forestry. However, other significant bio-based building primary crops include bamboo, reeds and hemp. Agricultural wastes and co-products from food production, such as cereal straw, also present opportunities for much wider use of natural materials in construction. As well as plant based materials there are animal based products such as sheep’s wool (insulation) and horse hair fibres (used in plasters).


Nature-based materials were the primary resources for traditional building prior to the industrial revolution. Natural materials avoid the high-energy production processes associated with many common materials and, as such, often have a lower embodied carbon. For timber, the majority of its embodied carbon is associated with energy-intensive kiln-drying. Despite this, timber structures typically have a lower embodied carbon than concrete or steel alternatives (Hart et al. 2021). Biobased materials play a key role in net-zero delivery through reduced operational energy use both directly, through reduced heating and cooling via latent heat exchange, and indirectly, from lower ventilation rates, passive humidity regulation, and wider indoor temperature range tolerance. Hygroscopic materials in general can reduce heating energy requirements by 2–3% and cooling energy requirements by 5–30% if integrated with a well-controlled HVAC system (Osanyintola and Simonson, 2006). There is demonstrated decreased risk of moisture deposits/condensation in construction elements and on interior surfaces incorporating nature-based materials (Latif et al., 2018) which leads to prolonged technical lifetimes of materials in addition to the clear occupant health and wellbeing benefits where interstitial moisture and surface condensation would lead to mould growth. Additionally, biobased materials exhibit excellent moisture buffering capacity which passively regulates room humidity further improving indoor air quality for reduced energy input (Latif et al., 2015).


Plant-based natural materials can be vital in achieving net-zero ambitions, as long as they are sustainably sourced. Biogenic carbon is sequestered by photosynthesis during the plant’s growth. When this carbon storage is credited to a building (as per current standards), it is possible for the building fabric to be a net store of carbon until the building’s end of life. Such temporary carbon storage has climate benefits, which increase the longer a component is in-use (Hawkins et al. 2021). For this reason, long lifespans and re-use of bio-based components should be encouraged. However, the effects of temporary carbon storage are not currently captured in a standard ‘static’ life cycle assessment (as reflected in the LCA standards described later). Ensuring sustainable harvesting practices and appropriate end-of-life considerations are critical for ensuring net-reductions in emissions.


Better understanding, and where necessary improving, the durability and resilience of these natural materials is essential if they are to have a substantial and sustained impact on reducing the construction industry carbon footprint and embedded carbon. More investment is needed in advancing innovative technologies applied to nature-based materials and solutions. In turn, technology-enhanced nature-based materials will be more durable and resilient. Thus, enabling efficient circularity of construction materials and achieving the Government's net-zero ambition (GSR 2020).



What role can the planning system, permitted development and building regulations play in delivering a sustainable built environment? How can these policies incentivise developers to use low carbon materials and sustainable design?


Full consideration for reuse of existing buildings should be required before considering demolition and new build. This includes possibility of exploiting historic overdesign to allow vertical extensions to a building. Most buildings have significant additional foundation capacity both due to overly conservative foundation design and overestimation of actual loading. This additional capacity can be utilised. May require strengthening to vertical load bearing elements of the building, but often these have significant extra capacity.


Building standards are used by designers to satisfy building regulations. Recommended live loadings for building should be reviewed; research has shown that actual loadings in buildings are far lower than design loads (Drewnoik and Orr, 2019). Planning authorities and building regulations should ensure that loadings used are appropriate and realistic for the development. In particular, mismatch between maximum occupancy levels associated with loading, ventilation, fire, etc should be identified.


Standards, should have an upper limit on design capacity. Utilisation of structural elements is often a very low percentage of their actual capacity due to overdesign and standardisation of elements within a building (e.g. consistent size beams, floor slabs etc, despite different loadings or spans). While there are requirements to meet design to lower limits on the capacity of structures, for safety, there is no upper limit on capacity that can be provided, i.e. optimization is rarely carried out to the extent it should be, in favour of standardization (Dunant et al. 2018). A limit on maximum overdesign could be considered to counter the wasteful use of resources which proliferates in the industry (Orr et al 2018). Likewise, structural serviceability requirements should also be reviewed: are current limits too onerous, given that full loading conditions are rarely, if ever, achieved?


Restriction on use of materials with higher embodied carbon could be considered. However, this requires a robust system to measure embodied carbon (such as the IStructE’s Structural Carbon Tool, although of course the structure is only part of the embodied carbon within a building). Designers and developers need to use materials with the lowest possible embodied carbon which still provides the functional properties required.



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


Standardisation of building-level embodied carbon calculations is vital for reliable comparisons between projects and, crucially, to enable carbon targets to be set and enforced by clients, designers or through legislation (e.g. planning permission). Thankfully, there is a growing consensus around embodied carbon calculation methodologies, as described in a number of guides.


Methods that determine the carbon footprint of buildings are based on life cycle assessment.  The underpinning standards for this are international: ISO 14040/44.  Based on this, there are specific standards for life cycle assessment of whole buildings (EN 15978:2011) and individual construction products (EN 15804:2019 or ISO 21930).


The RICS professional standard “Whole life carbon assessment for the built environment” (2017) accounts for both embodied and operational carbon in buildings.  It is based on EN 15978, and aims to improve consistency in carbon calculations by providing specific practical guidance for the interpretation and implementation of EN 15978.


Predicting carbon impacts earlier in the design process is critical because that is when there is more chance to influence design and minimise emissions. As a minimum, RICS requires a whole life carbon assessment must be carried out before the commencement of the technical design stage. RICS states that at least one other whole life carbon assessment should be conducted for each project after practical completion to represent the ‘as built’ carbon position. This will give the most accurate assessment of actual carbon emissions, which is useful for benchmarking and target setting on future projects.


LETI, GLA, RIBA 2030 Climate Challenge set targets for embodied carbon in buildings. LETI provides the most rigorous approach.


For new buildings, the embodied carbon is typically dominated by structural components. The IStructE’s 2020 guide enables structural engineers to quantify embodied carbon using a single document. Along with the accompanying spreadsheet tool, this has reduced the need for carbon consultants and led to a rapid increase in carbon assessment within the discipline.



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?


Yes. The UK is a net-importer of materials. If the manufacturing impacts are not taken into account, the greenhouse gas emissions associated with our choice of building materials in the UK will be missed.


Emissions from transportation are routinely accounted for in basic embodied carbon assessments. For example, both RICS 2017 and the IStructE’s 2020 guide require this.

For typical high-carbon materials, transportation emissions are small compared to those from material production. However, for bulky low-carbon materials, such as aggregates, transportation can be dominant.


As well as the overall distance, the mode of transportation has a major impact on emissions. For example, transportation of timber by road from Scotland to London (900 km x 0.107 kgCO2e/kg/km) emits more than three times as much carbon as transportation from Scandanavia by a combination of rail (200 km x 0.026 kgCO2e/kg/km), sea (1100 km 0.016kg CO2e/kg/km) and road (50 km x 0.107 kgCO2e/kg/km).



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?


Some of these can be accounted for in a full whole-life carbon assessment according to RICS 2017, or via the underpinning European standard EN 15978. The new CIBSE guide, TM 65, gives a method to account for the embodied carbon of building services.

Examples of past work that have quantified the carbon footprint of energy-generation systems for buildings include Allen et al (2015), with underpinning journal papers available on request.



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


The choice between refurbishment and new development should be founded on a careful balance between functionality, life-time performance, life cycle impacts, and whole life costs. Whilst re-use and refurbishment might be considered generally preferred, the whole life performance costs and carbon emissions need to be balanced against potential savings from a new development, especially one using natural materials with a net zero embodied carbon or better for example. There is no simple universally applicable answer.



What can the Government do to incentivise more repair, maintenance and retrofit of existing buildings?


A taxation system that encourages repair, maintenance and retrofit (reduced or zero VAT for example) compared to new build (currently zero VAT rated). Reverse this balance such that taxation rates are lower for existing building works.


May 2021




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