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LETI Unpicker: Retrofit vs Rebuild

This note provides guidance on how to compare whole life carbon for a retrofit versus its demolition and rebuild. 


In practice, there will be many factors in the decision of whether or not to retain a building, including:

→ Carbon: this is the focus of this note, considering both the embodied carbon implications, and the operational carbon implications related to energy use, in both the retrofit scenario and the demolish and rebuild scenario. 

→ Value such as heritage, benefits to users and the wider community.

→ Functionality and performance including comfort and flexibility of use.

→ Other sustainability considerations such as climate resilience, biodiversity and minimising water resources.


The initial embodied carbon emissions from demolition and rebuild will usually be higher than through retrofit, although extensive retrofit can also lead to high embodied carbon emissions. On the other hand, operational carbon emissions may be lower in a rebuild scenario, although deep retrofits can often approach similar operational carbon levels. On a whole life basis, the assessment is complex and relies on many assumptions.


This document aims to help review whole life carbon comparisons between rebuild and retrofit scenarios, to answer the following question:

Does the whole life carbon assessment and comparison provide a basis for decision on the carbon part of the Retrofit vs Rebuild argument?  

To answer this, this document helps establish whether the assessment and comparison are:

→ As fair and like-for-like as possible

→ Technically robust, thorough, and following best practice guidance

→ Transparent e.g. clearly listed assumptions, open about areas of uncertainty.


This is a simple document aiming to provide an overview for non-technical specialists.


Further Guidance

More detailed guidance is available in the following LETI documents:

 Operational energy and embodied targets and benchmarks: see LETI Carbon Alignment and LETI Climate Emergency Design Guide

 Operational Carbon in Whole Life Carbon Assessments Opinion Piece

 Upcoming guidance on Whole life carbon impacts of refurbishment vs new build and LETI Operational Energy Modelling Guide

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