Is it better to retrofit or build new in terms of life cycle CO2e Emissions?

Our research shows that well designed new build projects are similar in embodied energy per m2 when compared to retrofit projects.

The environment is one of our prime interests and one of the, if not the, most important factor(s) in the design our projects. For this reason we focus on systems for the evaluation and measurement of the whole life carbon emissions, from the beginning to the end, of each of our projects. A question that is debated regularly is whether it is better to build new or retrofit, the received wisdom generally being that retrofit generates lower embodied carbon (CO2e) emissions that new build. We wanted to test this rigorously using real world completed projects. Rarely is there a direct comparison possible but we wanted to do a detailed analysis so that we had verifiable data with which to consider this question. To that end we have spent some considerable time researching this issue on some of our completed residential projects.

We are currently using One-Click LCA software to estimate the life cycle carbon emissions of our projects this is an industry leading piece of software and recognised for its comprehensive database of specific products and materials.

As One-Click LCA allows full integration with our Revit models (all of our projects are modelled with Revit) we can directly import each material with their parameters in an automated, quick, and effective process. This allows us accurately and verifiably to calculate the embodied carbon for all elements of each of our projects and compare them on a per m2 basis.

The study compared our recently completed residential new-build housing project with recently completed residential retrofit projects. The calculations gave an interesting, and unexpected, result; our new build project achieved a very similar embodied carbon emissions compared to the refurbishment projects with values for embodied carbon in construction of 559 KgCO2e/m2 for the new-build housing and 460-560 KgCO2e/m2 for the retrofitted projects. It is worth noting that both results are within the LETI Design 2020 Target and RIBA 2030 target.

It is also worth noting that One Click LCA weighs a number of critical factors in the carbon emissions calculation, such as:

• The building material selection with their EPD (Environmental Product Declaration, provided by the material supplier and based on embodied energy in production),
•The material transport routes to site,
•The building operational energy.
•The water consumption.
•The operational energy used during construction.
•The carbonisation properties of materials.
•Disposal, recycling, and reuse of each material at the end of the building's life.

The outcomes noted above and the weighted factors used by the software analysis suggest that there isn’t a one rule fits all approach that can be taken; different projects, locations, and urban conditions (for instance) may call for a different project approach; retrofit or new-build. Only very good sustainable design for new build construction can compete with retrofit and requires a sustainable carbon approach from the early stages of the project supported by the client and all professional disciplines involved, and tested through the use of suitable software analysis to allow different options to be explored. And when refurbishing existing housing (or other building types) stock we cannot be complacent about carbon emissions in those projects, emissions can still be significant and need to be designed out wherever possible.

This data harvested with the software from completed projects is now used for our future projects and informs decision making as well as providing evidence based data from real world projects to inform the debate.