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Climate Emergency Retrofit Guide

LETI’s Climate Emergency Retrofit Guide shows how we can retrofit our homes to make them fit for the future and support the UK’s Net Zero targets.  We define energy use targets for existing homes and provide practical guidance on how to achieve them.  


The guide is useful for architects, engineers, Local Authorities, social landlords, energy professionals, contractors and clients looking for guidance about best practice retrofit.


It is widely accepted that retrofitting our existing buildings is absolutely critical if we are to achieve Net Zero.  Around 18% of our annual national CO2e emissions come from existing homes - homes that will still be standing in 2050. 80% of 2050’s homes have already been built.  It is also widely acknowledged that the retrofit challenge is monumental.  Over one million homes every year for the next 30 years will need to be retrofitted.  We cannot afford to retrofit them twice.  But if we retrofit them well, we can enjoy many environmental, social and economic benefits.


This guide sets out what good retrofit looks like for existing homes.   We target energy consumption reductions of 60-80% for the average UK home.  This is achievable through a whole house approach upgrading the building fabric, incorporating energy efficiency measures, improving ventilation and fitting heat pumps. These targets have been determined through practical experience and understanding of what measures are realistically achievable.  They are also informed by a national housing stock model to examine issues such as renewable energy provision and grid capacity. The guide also points out the potential risks of poor retrofit and advises on how to deliver efficient, resilient and healthy homes. 

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Quick Start Guide

The guide provides a quickstart guide to retrofit as well as typical house archetype examples for four primary housing types: semi-detached, detached, mid-terrace and a flat.  Click on the pages below for the quickstart guide and typical house archetype examples.

Typical house archetype examples

We have developed a series of typical house archetypes based on average data for each building type. We start with an existing pre-retrofit building and then show what happens when the LETI targets are applied. In some cases, we have used the LETI best practice ‘constrained’ retrofit values, the effect of an ‘unconstrained’ retrofit and an example of LETI exemplar retrofit.

Climate Emergency Retrofit Guide Launch webinar

Speakers & Panellists:


Clara Bagenal George, Elementa Consulting

Lynne Sullivan, LSA Studio & GHA

Antonia Khayatt, Architect

Martha Baulcombe, Burgess Architects

Will South, Etude

Federico Seguro, Troup Bywaters + Anders

Alex Whitcroft, KIN

Loreana Padron, ECD Architects

Sarah Lewis, Passivhaus Trust

Sara Edmonds, ACAN

Andy Simmonds, AECB

Federico Seguro, CIBSE

Jess Hrivnak, RIBA

Joanne Wheeler, UKGBC

Feedback survey

This document represents LETI’s understanding of how we need to be retrofitting homes to meet our climate change targets in 2021. This guide will evolve over time reflecting changes in carbon budgets, technologies and the capabilities of the industry. LETI is collaborative by nature and is very interested in your feedback.

→  Provide feedback on the Climate Emergency Retrofit Guide here


'We need to improve the UK's homes, fast and LETI’s excellent guide shows us how we can do that.  Their clear targets and straightforward guidance shine a light on how we must retrofit our homes.'


Alex Tait Head of Technical Practice, RIBA

'In 2050, 80% of all buildings that exist today will still be in use. The majority of those buildings aren’t green at all. That means retrofitting the millions of existing, carbon polluting buildings we have across the world, is one of the biggest challenges we face to make our planet green again. The LETI Climate Emergency Retrofit Guide clearly outlines how to do this.'  


George Clark Architect and TV presenter

A great and detailed guide that is a must-read for all designers entering the retrofit market. The setting of performance targets around 50kW/sqm/yr is pivotal for the market. We now need to develop the commercial, industrial and delivery approaches to realise these targets as an investable pathway to net zero, but LETI have thrown down the gauntlet to the housing sector and supply chain!'


Richard McWilliams Director, Sustainability Consultancy at Turner & Townsend and Programme Director for the Social Housing Retrofit Accelerator, the BEIS-backed Technical Assistance Facility for the Social Housing Decarbonisation Fund

'Homes account for 14 per cent of the country’s greenhouse gas emissions so retrofitting the country’s 29 million homes is a huge challenge that government and industry simply must get right. This comprehensive guide from LETI, aimed primarily at built environment professionals, could not have arrived at a better time.'


Will Hurst Managing Editor, The Architects’Journal

'Working collectively with LETI on developing this guide has been both a learning and empowering experience. We are all on a journey of upskilling amid the Climate Emergency, but we must do it quickly, and the collaborative approach is the only way. ACAN are focusing on both public engagement on retrofit, with the launch of our campaign Households Declare, and also cross industry collaboration working with and supporting other campaigns such as the AJ's Retrofirst campaign. We are excited for the launch of this guide as we truly believe it will serve the industry as a base platform for understanding the scale of the challenge but also inspire ways in which we can urgently, effectively, and safely address and replicate solutions at scale.'


Sara Edmonds ACAN

'All 33 of London’s local authorities have agreed a joint retrofit action plan to cut carbon emissions from the capital’s 3,781,477 domestic buildings and mitigate the capital’s impact on climate change. We welcome the publication of the LETI Climate Emergency Retrofit Guide: it will provide practical guidance to construction sector professionals - architects, designers, clients and contractors – on how to achieve successful retrofits.'


James McHugh Head of Housing Strategy, Waltham Forest Council

'URBED believe that to tackle the climate emergency we need to improve our existing buildings through high-quality, deep retrofit. Done well, this has the added benefit of improving health and reducing fuel poverty. LETI's practical, accessible, and evidence-based approach to improving understanding of climate concerns in the built environment is very welcome. This guide is an essential starting point for those who want to understand what is needed and what is possible when considering retrofit.'


Marianne Heaslip Associate Principal, URBED and co-founder at People Powered Retrofit

'Retrofit across the domestic stock is essential for the UK to achieve Net Zero, and this guide provides a compelling argument for it.  It demonstrates the need for a detailed whole house approach to retrofit to deliver carbon savings, improve health and comfort in the home and avoid detrimental effects. CIBSE look forward to continuing our work with LETI on this essential topic'


Julie Godefroy Head of Sustainability, Chartered Institution of Building Services Engineers (CIBSE)

'LETI’s new Retrofit Guide publication makes a crystal clear argument for retrofit.  Its easy to understand approach to considering how individual building components deliver holistic improvements will assists homeowners and built environment professionals alike.  This is an approach we have shown to work in the retrofit of CISL’s own retrofit of the Entopia Building – a leading retrofit office. The LETI strategy is not just useful for residential projects in the UK but also for professionals around the world looking for a clear approach to the residential retrofit process.'


Dr Kayla Friedman Built Environment Master’s Director, Cambridge Institute for Sustainability Leadership

'Retrofitting our existing housing stock is one of the most intractable problems facing us on our road to net zero carbon.It’s not easy: governments have failed over and over again to live up to promises. It’s not cheap: we often  underestimate the complexity of deep green retrofit. It’s not glamorous: the architectural profession is guilty of a lack of engagement. But it is absolutely essential that we focus on the 80% of our domestic buildings which leak carbon into the atmosphere at such a phenomenal rate. We need to start now educating a workforce of designers and builders who have the required knowledge and commitment : The LETI Retrofit Guide tells us how to do it.'


Peter Clegg Senior Partner, Feilden Clegg Bradley Studios

'The National Energy Foundation welcomes LETI’s ‘Retrofit Guide’ which represents the culmination of leading cross sector research. While comprehensive the guidance is easy to follow, logically structured and well presented. I’m sure this guide will be well received and act as an ongoing point of reference for driving up retrofit standards and positive outcomes'


Paul Ciniglio Refurbishment Lead, National Energy Foundation

'This is exactly the guide that the retrofit industry needs.  It combines a comprehensive description of the whys and hows of retrofit with guidance about retrofit strategies, explanation of technical complexities, robust performance standards and clear explanations of how to plan and implement retrofit projects.  Now that we have this guide there is no excuse for us not to rise to the challenge of climate change and get on with retrofitting UK homes.'


Dr Peter Rickaby Technical Director, The Retrofit Academy, Chair, BSI Retrofit Standards Task Group

'Retrofitting the UK’s existing building stock must be delivered at pace in an informed and considered way – otherwise we risk diluting the significant economic, environmental and social benefits of this important work.  The LETI Climate Emergency Retrofit Guide shares wisdom from experienced partners and will be an invaluable tool in improving the environmental performance of buildings.  As owners and occupiers of heritage assets, we welcome this pragmatic and holistic guide signposting best practice, which we will incorporate into our own £90 million retrofit programme.


Victoria Herring Director, Sustainability Programme, Grosvenor Britain & Ireland

This is the comprehensive guidance I have long been hoping for. One of the key challenges we face for any given building is to decide what reduced level of space heating to target. I particularly welcome the advice on determining the optimum amount of insulation to deliver best value.


Christopher Jofeh Chair, Welsh Government’s independent advisory group on residential decarbonisation

'Our existing buildings are by far the biggest culprit of carbon emissions from the built environment – and therefore also pose the biggest potential for carbon savings. We must seize the opportunity to address the Climate Crisis AND radically improve the health and wellbeing of millions of households. We hope this timely guidance, along with several additional new PHT design tools, will drive urgent deep retrofit into action at scale. The Trust welcome detailed analysis that sets EnerPHit into context as the exemplar retrofit standard.  LETI is a shining example of what cross-industry collaboration can achieve – we look forward to much more of this!' 


Sarah Lewis Research & Policy Director, Passivhaus Trust

'The Retrofit of existing buildings housing is one of the biggest challenges facing Housing Associations committed to getting to Zero Carbon. The LETI guide is a welcome resource to help us develop a more strategic approach to decarbonising our existing housing stock and minimising heating costs for our residents. It is an informative resource, authoritative and wide ranging. It will help housing associations such as Peabody with many older housing estates think through the task of balancing the multiple challenges of retrofit, fire safety and maintenance.'


Dick Mortimer Executive Director of Development & Sales, Peabody

'The majority of homes that will exist in 2050 have already been built, so making them more energy efficient must be very high on any Government’s agenda. This splendid report sets out how this can be done, as well as the very real pitfalls in making seemingly simple changes to a home’s ventilation and insulation. What we need now is a well-organised and well-funded Government initiative to meet this challenge'  


Peter Murray Curator-in-Chief, NLA

'I am really looking forward to the LETI retrofit Guide. Their Climate Emergency Design Guides were a game changer in the industry, bringing low carbon design and embodied carbon to the fore. I regularly refer to my copies as we try to design to meet the targets'

Julia Barfield Director, Marks Barfield Architects

'Architects Declare fully support the LETI Climate Emergency Retrofit Guide and applaud the hugely talented team behind this well-timed publication. We acknowledge the importance of prioritising the retrofitting and re-use of the existing built environment over demolition and new build if we are to have any hope of meeting Net Zero Carbon targets for 2050. Whilst we appreciate the challenges that successful low carbon retrofit presents the architecture profession, like LETI, we believe that our industry has the collective knowledge and expertise to step up and meet this head-on.'


Architects Declare UK Steering Group

'Everyone interested in action on the climate emergency knows that without massively reducing the energy usage in our existing building stock we have zero chance of achieving Net Zero. Everyone knows but few act. LETI shows us what we must do and how in its customary plain speaking, well-evidenced and quietly passionate way.'


Sunand Prasad Principal,Penoyre & Prasad

'This comprehensive guidance is centred around delivering the real-world thermal performance levels we need to address climate change and achieve lowest cost decarbonisation of our homes and the UK’s energy system.'


Jon Warren, Energiesprong UK

'In the context of the Climate Emergency, we believe deep retrofit is absolutely central to meeting our obligations under UK and international climate change agreements. Furthermore, we believe householders and citizens must be put at the centre of the retrofit revolution, to offer legitimacy and ensure the development of effective, user-centred solutions. LETI have provided expert knowledge and guidance in this area, their work is essential in helping the UK achieve retrofit at the pace, but as importantly at the quality, we require. This new report is central to that work.'


Jonathan Atkinson co-founder-Carbon Co-op and People Powered Retrofit

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