LETI (London Energy Transformation Initiative)              SBE0137

Written evidence from LETI (London Energy Transformation Initiative)


The London Energy Transformation Initiative (LETI) is a network of over 1000 built environment professionals that are working together to put London on the path to a zero carbon future. The voluntary group is made up of developers, engineers, housing associations, architects, planners, academics, sustainability professionals, contractors and facilities managers.


LETI has been instrumental in affecting change in the construction industry, having released a number of landmark documents and been involved in the development of planning policy in London and beyond. Some of LETI’s publications to date include;


-          Net Zero 1-Pager (2019)

-          Climate Emergency Design Guide (2020)

-          Embodied Carbon Primer (2020)

-          Hydrogen: A decarbonisation route for heat in buildings? (2021)


All of these documents are free to download from LETI’s website - www.leti.london


Executive Summary


§1 First, to state the significance of the crisis at hand. ‘Leading scientists now say that unless we change course drastically, within the lifetime of people alive today, we are heading for a world which can support only 0.5 to 1 billion people. Such is the climate and ecological emergency. The warnings could not be more serious. We need all our cities and communities, let alone buildings, to be zero carbon without delay.’ [i]


§2 In the appendix at the end we have opted to write a brief summary of the documents that LETI has released to date and is working on, because the breadth of these are too vast to recount in 3000 words.


§3 In short however, we have managed to achieve widespread consensus within the construction industry and our network around the targets and guidance we have set out.


§4 We regard the LETI guidance documents as illustration of the readiness of the construction industry to meet the UK’s net zero targets, with the right motivation from government. We have managed to define what ‘good’ looks like in the current planetary emergency, and we now need the government to take note of this, and ensure that all new policies affecting the built environment are delivering what is necessary.

§5 We have answered each of the questions from the inquiry but we believe that by adopting the lessons shared in the LETI pathway documents, that have been written by every profession linked to the built environment, the government has the basis of a really through and developed framework.

§6 We hope that this response is of use to the inquiry, and that the inquiry will call upon LETI to give further evidence,





Q1. To what extent have the Climate Change Committee’s recommendations on decarbonising the structural fabric of new homes been met?


§7 The recommendation largely revolved around increasing the use of timber. This approach has been hit hard as a result of the Grenfell Tower Tragedy with some local authorities pulling away from all applications of combustible materials not just in the façade but the frame too.


§8 Insurance companies are also known to be putting off developers from using combustible materials beyond just the building façade.


§9 Clients are using the combustible material argument throughout developments to validate value engineering cost cutting exercises from timber to steel or concrete. 


§10 A recommendation at the government level will not have significant impact without regulation to design low-carbon and clear and accurate guidance on safety of these low-carbon materials.


§11 It should also be noted that this approach is an overly simplistic approach. The decarbonisation of the structural fabric is not just limited to material choice. We need to ensure that the waste and procurement strategies are also included within this approach. For example whilst timber has significant low-carbon benefits we need to be confident of the circularity of this material and we need to ensure that the timber is truly from sustainable sources. There is a significant amount of timber that is used in formwork, which whilst does come from FSC timber sources, however it’s re-use potential can be limited and in a very short space of time the carbon sequestered within this timber will find its way back into the atmosphere.



Q2. 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?


§12 Within the Embodied Carbon Primer we have outlined sections on different materials in Appendix 8 – Material Guides.


§13 It is again possibly a little too simplistic to think that all buildings should be from one material type. There are rules of thumb but a whole life carbon assessment should be undertaken to ensure the correct balance is achieved. The benefits in using timber as a building frame are plentiful and we have outlined above the necessary considerations that need to be in place when pursuing this material, however we must consider that there are opportunities to reduce the carbon impact with traditional building materials. This may create a bit of work but with aluminium and steel, for example there are opportunities to specify materials with high-recycled content within them. This will impact the traditional procurement approach and can impact lead-in times, sourcing and design. Whilst the carbon impact is not likely ever to be lower than timber it needs to be recognised that we will still need to rely on these higher carbon materials in the next 10-15 years which is the absolute critical time zone for embodied carbon reduction.


§14 Again, this is where regulation can assist. With an awareness at present that the maximum low carbon choice material will likely come with an impact on time, cost and design then without a progressive and engaged client these low-carbon choices will often be shelved. Regulation needs to be careful that it allows flexibility in the design and does not result in only one material or manufacturer being able to deliver.


§15 Also, buildings often have a lot of redundancy in their design, particular on the building envelope. Architectural features should be used to benefit the visual experience whilst also passively assisting a building to run at low heating or cooling levels. This could be incorporating features as static shading devices whilst ensuring the are using low-carbon material options.



Q3. What role can nature-based materials can play in achieving the Government’s net zero ambition?


§16 As indicated above nature-based materials can be significantly low-carbon however a clean chain of custody needs to be in place and an end-of-life/circularity pathway should be developed.


§17 It should be noted that for some natural insulation materials the depth of the build-up required to achieve the same thermal performance as artificial insulation materials can lead to a higher embodied carbon quantity in extreme cases with additional material depth and additional framing and plating layers . Therefore again considering the whole picture is required. At LETI we like to present materials as how to deliver them low carbon (if possible) and what the implications are for that.


Q4. 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?


§18 This is imperative that we get this right. Regulation and target setting will help to drive toward low carbon materials. However, they need to be in balance with operational carbon.


§19 To that end both planning and building regs need building standards for whole life carbon.


Q5. What methods account for embodied carbon in buildings and how can this be consistently applied across the sector?


§20 RIBA, IStructE, CIBSE and RICS have all released how to guides/notes on methods to account for EC in buildings, These are based on ISO standards 14011 and EN 15978. There is always some ambiguity about what carbon factors are used and what materials are included. The GLA has developed a framework for this with guidance from industry. Also see LETI Embodied Carbon Primer.


§21 EPDs are often used to determine carbon factors. A cautionary note on EPDs is that there quality can be questioned, they do not all include the same life cycle stages, they do not confirm environmentally responsible products and an over reliance on an EPD to confirm environmental performance can restrict market access for start-ups and less popular products due to the cost of an EPD. They probably need to be better regulated and subsidised if that path is taken.


Q6. 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?


§22 Absolutely. Materials that are deemed ‘green’ should not be exempt from having their whole product life-cycle considered.


Q7. How well is green infrastructure being incorporated into building design and developments to achieve climate resilience and other benefits?


§23 Rarely but starting to see it more with more switched on clients and those with WELL ambitions. Green infrastructure is rarely considered as a carbon sequestration resource as often outside the project boundary for carbon counting.



Q8. 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?


§24 It is imperative that these elements are included in a whole life carbon assessment. For a number of years “sustainable” measures have been given exemptions from these assessments however this has led to an element of ‘green-wash’ on buildings.


§25 To enable a smooth journey through planning renewable energy, water conservation measures etc are often proposed to appease planners with only the positive impacts monitored and not the upfront or recurring embodied carbon impacts. For instance building integrated PV cells can be very inefficient in terms of energy production. They can also have a large upfront carbon footprint and need replacing every 20-30 years which is how long a typical warranty lasts.


§26 However the energy production they produce is often only reported on which can take many decades to payback the upfront and recurring embodied carbon footprints.


Q9. How should re-use and refurbishment of buildings be balanced with new developments?


§27 To achieve net-zero we have to re-use and adapt. There is not another option. We can not get to our carbon targets with current materials, grid and resources available to us. However the re-use/refurbishment of a building must be fully considered. Can this facility have the same service-life as a new-build alternative? Are there greater opportunities for adaptability with a new build?


§28 It is very difficult to weigh this up based on carbon counting alone and so it is important that a meaningful narrative is developed.


Q10. What can the Government do to incentivise more repair, maintenance and retrofit of existing buildings?


§29 LETI is about to release a Retrofit Guide, outlining best practice for the necessary retrofit of the existing building stock we have in the UK. This retrofit will improve the energy efficiency and quality of the existing building stock for residents and occupiers alike. This will also help to ensure that the carbon already sequestered in our existing building stock stays as a carbon sink of sorts, and help to avoid unnecessary demolition of potentially useful buildings.


§30 The guide also will develop on what policy/financial incentives are needed. We encourage government to take the lessons from the guide to assist this inquiry.


§31 And to finish, removing VAT is always the answer given by clients.


§32 And finally to finish, also not covered here but should very much be mentioned, offsets should not provide the easy option out for developers and I would suggest that clarity on products pertaining to be zero-carbon needs to be


May 2021


Appendix – Supporting Information


  1. We are in the process of developing a number of relevant guidance documents and research projects including;

1.1.   A retrofit guide – outlining best practice for the necessary retrofit of the existing building stock we have in the UK. This retrofit will improve the energy efficiency and quality of the existing building stock for residents and occupiers alike. This will also help to ensure that the carbon already sequestered in our existing building stock stays as a carbon sink of sorts, and help to avoid unnecessary demolition of potentially useful buildings.

1.2.   A clients guide outlining best practice for clients in the UK to deliver net zero compatible building developments.

1.3.   One-pagers for Embodied carbon and Whole Life Carbon - release summer 2021

1.4.   Circular Economy guidance - release Autumn 2021

1.5.   Procurement guidance- release Autumn 2021

1.6.   Case studies of low embodied carbon exemplars

1.7.   LETI Pioneer Projects projects that will seek to achieve the KPI targets set out in the Climate Emergency Design guide.

  1. Our existing guidance documents are as follows;

2.1.   Climate Emergency Design Guide

2.1.1. We are in a climate emergency, and urgently need to reduce carbon emissions, this guide outlines the requirements of new buildings to ensure our climate change targets are met - setting out a definitive journey, beyond climate emergency declarations, into a net zero carbon future. It is specifically aimed towards developers/landowners, designers, policy makers, and the supply chain. It aims to help to define ‘good’ and to set clear and achievable targets.

2.1.2. The Climate Emergency Design Guide covers 5 key areas: operational energy, embodied carbon, the future of heat, demand response and data disclosure. Our methodology includes setting the requirements of four key building archetypes (small scale residential, medium/large scale residential, commercial offices, and schools). The guide was developed by over 100 LETI volunteers over a period of 12 months.

2.1.3. This guidance demonstrates that the building industry knows how we should be designing buildings. In 2020 buildings that adopt these requirements now will be seen as leaders. By 2025 these requirements must become standard design practice otherwise the building industry will not meet our collective responsibility in this climate crisis.

2.1.4. LETI believe that in order to meet our climate change targets, in 2020 10% of all new projects developers and designers are involved in, should be designed to meet the requirements set out in this guide. Design teams will have the opportunity to register their projects as LETI Pioneer projects, to share knowledge and overcome barriers with other design teams working towards the same goal.

2.2.   Embodied Carbon Primer

2.2.1. The Embodied Carbon Primer offers supplementary guidance to the Climate Emergency Design Guide, for those interested in exploring embodied carbon in more detail. There is a current lack of knowledge in the built environment industry surrounding embodied carbon reduction strategies and calculations. Therefore, the London Energy Transformation Initiative has produced this document to support project teams to design buildings that deliver ambitious embodied carbon reductions.

2.2.2. This document is intended to provide designers including architects, engineers, interior designers and urban designers with easy-to-follow best practice and toolkits for reducing embodied carbon in buildings. The document can also aid planners to be aware of strategies available to designers to reduce embodied carbon in building design, and how planning recommendations on materials, massing and treatment of sites may affect embodied carbon.

2.2.3. For everyone working in the construction of buildings, the leap of knowledge and skill required to be able to fulfil this goal is still relatively large, but far from insurmountable.

2.3.   Net zero one pager

2.3.1. 2019 was a watershed year. The climate emergency was widely acknowledged and widespread support was established for an acceleration of the transition to Net Zero Carbon.

2.3.2. By 2030 all new buildings must operate at net zero to meet our climate change targets. This means that by 2025 all new buildings will need to be designed to meet these targets. We therefore have five years to do it progressively so that it becomes the norm in 2025. We should start now.

2.3.3. Industry consensus has been established on the key features of Net Zero Operational Carbon buildings. This new 1-page summary was launched by the London Energy Transformation Initiative (LETI) on 16.12.19 at Feilden Clegg Bradley Studios. 

2.3.4. This document is the result of a very successful industry consultation with more than 330 responses and has been developed in collaboration with the UK Green Building Council (UKGBC) and the Better Building Partnership (BBP). It  is also supported by the Good Homes Alliance (GHA), the Royal Institute of British Architects (RIBA) and the Chartered Institution of Building Services Engineers (CIBSE).

2.4.   Hydrogen research paper

2.4.1. Hydrogen as a means to deliver energy is often touted as a viable solution to assist in meeting the UK’s net zero carbon target. This has a major influence on the need, or otherwise, to enhance new-build energy efficiency and the energy retrofit of our existing stock. Why enhance our buildings if the current use of natural gas can be simply switched to zero-carbon hydrogen?  

2.4.2. LETI have therefore sought to investigate this further and examine to what extent hydrogen is likely to be used, either in part or fully to accompany decarbonisation of the electricity grid. With the considerable hydrogen media hype, the aim has been to harness LETI’s non-aligned approach to navigate through the mass of vested interests to gain a more realistic understanding of its potential for heat in buildings.

2.4.3. Hydrogen is an energy carrier and so critically important is where it sources this energy and whether it is actually zero carbon. In a post-Grenfell era, it is also vital to understand issues like where liability lies for the repurposed gas pipes for combustion in our homes. Any zero-carbon grid switchover comes with high costs and so for building occupiers / owners who pays and its impacts on the fuel poor are also key issues. Is it destined to pick up the mantle as the low-cost fuel for the vast majority of buildings, or as a higher cost fuel for more niche markets exploiting its particular unique characteristics? 

2.4.4. This document acts as a concise primer for those seeking clarity on the likelihood of hydrogen becoming a means of heat delivery for buildings via the pre-existing gas pipe network. It is based on an extensive review of published documents from a broad range of viewpoints. For those who wish to dig further, an extensive reference list is included.

  1. Summary

3.1.   All the aforementioned documents have been widely adopted within the construction & built environment sectors. Thousands of homes around the UK are now being delivered to meet the targets we defined in our Net Zero one-pager and Climate Emergency Design Guide – we are seeing local authorities and private sector clients alike adopting our guidance as their briefing benchmarks for projects.

3.2.   We have achieved industry consensus around benchmarks, and we have submitted evidence in full for the Future Homes Standard Consultation with this in mind.

3.3.   We believe these documents are of significant relevance to the inquiry and we would appreciate the inquiry taking the time to review these documents in full, hence our preference to not answer questions as listed by the inquiry.




[i] Desai, Pooran OBE Hon FRIBA (2020) LETI Climate Emergency Design Guide



Climate Emergency Design Guide: https://www.leti.london/cedg

Embodied Carbon Primer: https://www.leti.london/ecp

Net Zero 1-pager: https://www.leti.london/one-pager

Hydrogen: A decarbonisation route for heat in buildings: https://www.leti.london/hydrogen