JLL looks at Net Zero Carbon targets for building retrofit projects
Guide
Net Zero Carbon Retrofit – Rebalancing the Requirements
Alternative EUI targets for Existing Commercial Buildings
The LETI 2030 NZC targets for new commercial buildings are an operational EUI of 55 kWh/m2 and embodied carbon of 350 kgCO2/m2. The EUI performance is consistent with the current LETI 2020 target however the 2020 embodied carbon target is 600 kgCO2/m2. A limit of 600 kgCO2/m2 of embodied carbon is very testing for new build and arguably currently undeliverable. The 2030 embodied carbon target assumes a very significant 50% reused content implicitly suggesting new build will be retrofit with new build additional floors or a building extension!
Our alternative EUI targets proposals use the LETI 2030 EUI & embodied carbon targets.The LETI Embodied Carbon Primer guidance provides details on the anticipated whole-life carbon (WLC) of the ultra-low energy new commercial building i.e. NZC 2030. The simple breakdown is materials & construction: 38%, operational energy: 28%, maintenance: 32% and disposal: 2%.
The same guidance also provides a breakdown of the materials & construction with approximately 81% allocated to substructure, superstructure & facades with finishes & mechanical, electrical and plumbing engineering (MEP) at 19%. This breakdown is clearly based on a new build and as we transition from 2020 to 2030 the vast majority of the targeted embodied carbon savings will come from the substructure, superstructure & facades rather than finishes & MEP.
Although NZC targets and the breakdown of WLC % allocations are presented definitively, in reality there is a huge variance in the figures in the supporting information and, at best these should be considered as indicative.
If we assumed that a NZC building retrofit requires the full replacement of the MEP systems, new finishes throughout along with a range of internal layout changes a budget for 150 kgCO2/m2 or 25% of the 2020 embodied carbon target would seem reasonable within the context of the LETI guidance. If we then assumed that all the projected embodied carbon savings to 2030 came from the substructure, superstructure & facades then at 2030 the retrofit embodied carbon allocation would remain 150 kgCO2/m2 or approximately 42% of the 350 kgCO2/m2 NZC new build embodied carbon target a saving of 58%.
Returning to the ultra-low energy new commercial building WLC allocations for materials & construction, operational energy, maintenance, and disposal. If the assumed NZC building retrofit saves 58% of the materials & construction budget, then this can equitably be reallocated to the operational energy budget without detracting from the WLC target. This would increase the operational energy budget from 28% to 50% (58% of 38% is approximately 22%). The impact on the EUI value would be an increase from 55 kWh/m2 to 98 kWh/m2.
In broad terms the WLC impact of a building achieving the 2030 NZC EUI & embodied carbon targets of 55 kWh/m2 and 350 kgCO2/m2 is equivalent to an EUI of 98 kWh/m2 and 150 kgCO2/m2.
The higher EUI takes advantage of the inherently low embodied carbon involved in an existing building retrofit without sacrificing the projects WLC while also providing a significantly more affordable retrofit.