Building performance, embodied carbon, responsible material use and circularity are the drivers for sustainable buildings. Digital technology is used in smart systems to support processes for environmentally friendly design, construction, and operation. This chapter analyses the balancing act of Modern Methods of Construction between innovation and climate emergency. It discusses the latest innovations embedded in prefab systems to deliver low-carbon systems, advance circularity in the built environment and retrofit the existing building stock. This section draws a methodology to assess the sustainability performance impact on inhabitants, to reflect upon the complexity of delivering indoor comfort in a changing climate. It reflects upon life-cycle analysis of prefab systems developed to be highly energy efficient and seismic resilient, while reducing carbon footprint. It opens up to the challenges of deconstruction and reuse, discussing the opportunity to reuse lightweight façade systems to shed light on the carbon benefits of closing the loop.