OPINION | CARBON RETROFIT TARGETS The upfront carbon of retrofitting an existing office is a fraction of that in a new-build, but this is not yet recognised in net zero targets, says JLLs David Bownass, who puts forward his recommendations for operational energy and carbon targets UPFRONT ON CARBON N et zero carbon (NZC) retrofit is more complex and expensive than new build. Its also the largest part of the market requiring improvement if the UK is to reach its 2050 NZC goal. Retrofitting existing office buildings has a significant benefit over building new NZC offices; the upfront carbon of the retrofit is a fraction of that in a new build. Upfront carbon is carbon in construction & materials (embodied carbon is everything except operational carbon [energy & water] & circular economy.) Conversely, reducing energy demand in existing buildings is more difficult. These differences are not recognised in the application of current NZC office guidance. The new build NZC office operational energy target of 55kWh.m-2 per year gross internal area (GIA) and upfront carbon (design target C rating) of 600kgCO2.m-2 targets are the same for retrofit and new build. Carbon emissions are the same irrespective of their source, a kilogram of upfront carbon is the same as a kilogram of operational carbon. A more pragmatic approach to NZC retrofit is required. Our research suggests NZC retrofit can be constructed to alternative operational and upfront carbon targets while achieving the same whole life carbon (WLC) outcome. Our recommendation, for broader market discussion, is that NZC retrofit should have an operational energy target of 80kWh.m-2 per year (GIA) with an upfront carbon target of 258kgCO2.m-2. This provides the same WLC outcome and acknowledges the differences between retrofit and new build, while improving the financial business case and encouraging more NZC retrofit activity. The aim of the article is to start a conversation about appropriate retrofit NZC targets. Retrofitting existing stock is the NZC priority, given that most buildings in the UK today will still be in use in 2050. The UK Green Building Council (UKGBC) and London Energy Transformation Initiative (LETI) NZC guidance is geared towards new build, although currently it is also applied to existing buildings. This is understandable because, historically, the construction market has focused on new build, but in future this will not be the case. Current UKGBC and LETI guidance is just the start of the NZC journey and further guidance will no doubt follow to cover different building types, WLC and, hopefully, existing buildings. Its also possible that energy use intensity (EUI) targets may change if the projected UK renewable energy-generation capacity increases markedly. LETI acknowledges this, and considers current EUI targets are indicative and should be refined in future.1 LETI recognises the existing building challenge and states: We will not be able to retrofit existing buildings to the same levels of fabric efficiency (as new build) so we need to accept they will need to take a disproportionate share of the (renewable energy) budget.2 This is useful, but doesnt quantify a proposed increase in EUI for NZC existing buildings. The need for further work on the NZC requirements for existing buildings is acknowledged and may even be planned. Meanwhile, the market doesnt stop, and the requirement for further clarification is acute, as existing building NZC business cases must be justified. Existing buildings retrofit issues Retrofitting existing buildings to NZC is more difficult and, proportionally, more expensive than new-build NZC, which makes the retrofit business case more challenging. The reasons for this include: The value of a building when it is complete and in operation is influenced primarily by its rent streams. As NZC buildings are new to the market, evidence of any premium associated with these inputs for a building that has had a significant NZC cost to retrofit is not 40 September 2021 www.cibsejournal.com CIBSE Sep 21 pp40-42 Net zero JLL.indd 40 27/08/2021 16:16