The **BUNZ (Build-Up Net-Zero)** concept creates a new sustainable model for creating desirable net-zero performance-guaranteed new homes, whilst retrofitting existing homes to net zero. Energiesprong UK (ESUK) was set up to drive forward the market for desirable, performance guaranteed, net-zero homes, and support innovation to deliver them. We work between social housing providers and the supply chain to help create whole-house solutions which improve quality and which can be rapidly scaled to meet the UK's climate challenge. To date three pilot projects have been completed across five landlords, with further projects underway. In 2019 ESUK identified an opportunity for a build-up model, where new apartments are built on top of existing blocks, which are retrofitted to net-zero standards at the same time. BUNZ addresses many of the challenges set out in the Construction Sector Deal. It supports the target for 1.5m new homes by 2022, it uses digital design and offsite manufacturing. It drives collaboration between client and supply chain. It uses whole-life asset value, and it exceeds the target for halving the energy consumption in new and existing buildings by 2030, instead ensuring homes are retrofitted and built to 2050 standards - net zero. The offsite manufacturing approach driven by the Energiesprong standard drives improved quality and performance, reducing site times. This is even more important post-C19, when reduced access to homes, and limited site working practices are driving up construction delivery period and costs. Residents can also remain in situ. Exeter City Council has identified a pipeline of apartments and this funding will allow the development of the procurement approach to overcome the short-term stop-start typical approach to construction projects. Focusing the procurement on the whole-life performance and cost also changes the relationship between client and supplier. Energiesprong will work with the DEEP-ER consortium (led by Prewett Bizley and KIN) to deliver the project. BUNZ allows the creation of affordable new homes without encroaching on green spaces, providing an opportunity to reduce overcrowding associated with worse COVID outcomes. Our solution will use new homes as an opportunity to improve the business case for retrofitting to achieve UK net-zero goals.