Dr Jim Carfrae, Dr Matthew Fox, and Professor Steve Goodhew              SBE0031

Written evidence from Dr Jim Carfrae, Dr Matthew Fox, and Professor Steve Goodhew


From The CobBauge Project, University of Plymouth, Devon, PL4 8AA.


We are team of professional researchers from the University of Plymouth, specialising in working with innovative natural building materials.


We are experienced in building performance evaluation (BPE), the assessment of low environmental impact materials and sustainable construction methods, including the author of Wiley’s Sustainable Construction Processes. We welcome the call for evidence and expertise as part of a deeper inquiry into the sustainability of the built environment.


To what extent have the Climate Change Committees recommendations on decarbonising the structural fabric of new homes been met?


The CCC has two main linked recommendations.




Increasing use of timber in construction will require considerably more high-quality kiln dried sources of lumber which is likely (as the report describes) to increase low quality by-products, some only fit for biomass energy.


If policies encouraging the use of medium quality agricultural waste such as waste straw and other fibres in construction products, both structural and insulative, it is likely that innovative new products and upscaled vernacular methods will introduce alternative carbon sinks and avoid landfill.



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?


Currently there is an imbalance between materials that offer high levels of energy efficiency but involve complex manufacturing processes that lock in high levels of embodied carbon. Whilst minimising energy demand from buildings in use is a justifiable and important target for energy efficiency, this perspective deals primarily with future carbon emissions. Indeed, standards such as part L of the England and Wales building regulations, and the international PassivHaus standard have made excellent progress in reducing energy in use from buildings. Yet these standards fail to acknowledge or address the increasing amounts of energy it takes to deliver these buildings.


It is becoming clear that the UK, in leading the global construction industry should be re-focusing their perspective on sustainable construction. This needs to involve a paradigm switch from the current mono-perspective, which focuses solely on energy in use to one that prioritises low carbon materials alongside good levels of energy efficiency. This new holistic approach to sustainable development will enable the UK to not only consider carbon reductions in the “future”, but also importantly, the “now”. 


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?


There are many ways of calculating the embodied energy of the building process, and each can produce a different result. Broadly speaking, if you calculate the energy in use of a PassivHaus built with conventional materials over 60 years and compare it to the embodied energy contained in the materials used to construct it, then embodied energy will be at least half of the total energy emitted by that building. As stated earlier, that embodied energy is being released into the atmosphere now, unlike the gradual release of the energy used in heating and cooling the building.


By employing a more holistic approach to reducing carbon from buildings, the pressures present in delivering ultra-low energy consuming buildings becomes less. For example, buildings constructed to the PassivHaus standard require highly complex systems to achieve compliance, yet such high standards of energy efficiency might not be as imperative if embodied carbon in construction is considered equally as important.


With a holistic approach it might be acceptable to permit materials with a slightly higher thermal transmission value that can then be offset by the embodied carbon of the material during production and construction. This could be applied in a similar manner to the way Part L of the building regulations used to be applied, where one part of the building fabric with a higher thermal transmission value could be offset against other areas of the building with lower transmission values. In this proposal we are suggesting that the trade-off should be between the thermal transmission of the selected material and its embodied energy. Where a material with a slightly higher thermal transmission value is accepted by building control on the basis that its embodied energy value is low. 


We advocate that the trade off in thermal transmission value against embodied energy is achieved in practice by using either a Life Cycle Analysis (LCA) approach developed through the building regulations or by utilising an existing LCA methodology such as the Inventory of Carbon and Energy (ICE), developed by Circular Ecology. The ICE Guide can be enlarged to take into account these alternative materials to give specifiers the ability to undertake simple calculations to back up their claims.


The use of a simplified life-cycle assessment procedure based on an enlarged database already contained in the ICE offers a system that can be updated over time as the knowledge base of different materials becomes more readily available.


When looking at the embodied carbon impact of alternative materials the energy and carbon cost of manufacture is definitely a substantial element and a life-cycle assessment procedure can take into account both this and the delivery carbon costs associated with getting the materials to site.

Without a such a shift in focus to a holistic approach to carbon reduction and the appropriate change in the legislation, it is perceived that the industry will continue to develop and use materials with high embodied energy. We see this as hindering the development and adoption of natural building materials.


Natural building materials are not new. In fact, historically, all of our buildings were constructed from natural materials. Yet with the introduction of more modern man-made materials, the UK has lost much of the inherent knowledge and expertise in natural materials.


Requiring fewer processes than man-made materials, natural materials by virtu often have the least embodied energy of all construction materials. They also bring a range of additional proven benefits, such as moisture regulation, ease of recyclability and low toxicity, which can lead to improvements in indoor air quality (IAQ) and healthier indoor environments. Yet natural materials often struggle to comply with current legislation and building standards on thermal performance. The way these standards are structured favours highly complex man-made materials, which are specifically manufactured to deliver the greatest performance regardless of how much energy it takes to achieve this final performance.

As an example, we would like to draw attention to cob as a traditional UK material, which demonstrates the problem with the UK’s current mono-perspective on carbon reduction. Cob is an unbaked earth construction that has been used for many hundreds of years in many places across the UK and form part of the vernacular landscape. This material offers many unique benefits, such as being structurally performing, hygroscopic and enabling the use of stored thermal mass to regulate indoor temperatures throughout the year. However, it’s primary attribute is the ability to source the material from the ground on which the building stands, thereby resulting in a material that has a very low embodied energy and enhanced local identity. Yet currently, this material does not comply with UK legislation on thermal conductivity.   This places an obstacle to the application of a material that could lead to very low carbon footprint by all other means.


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


‘The most efficient basis for a sustainable building is the one you already have Whilst that statement doesn’t take into account location, historic building status and inherent structural issues, most buildings can be effectively refurbished. It may take longer and compromises made but the non-exception of VAT on large scale refurbishments alongside the difficulties meeting all of Part L make for a significant disincentive. It is therefore recommended that a ‘trade off system is introduced off setting lower U-values against the use of materials with a lower embodied energy. This could also be set against better U values elsewhere in the buildings in an area by area approach.


For the UK to truly become a world leader in minimising carbon emissions and addressing the climate emergency, we feel certain that the UK should change from a mono-perspective to a holistic approach when considering sustainable construction. We also advocate the use of natural materials as a key component in achieving this target.


We would welcome further discussion, clarification and engagement on this subject.


Yours faithfully


Prof Steve Goodhew

Dr Matthew Fox

Dr Jim Carfrae


The University of Plymouth Natural Building Materials Research Team.

The CobBauge project: www.cobbauge.eu



May 2021