## 2 Literature Review
### Life Cycle Thinking  
Life cycle assessment has been used as a decision support tool to evaluate the environmental performance of buildings. It enables identifying hot spots, avoiding problem shifting, and making informed decisions. There have been many advancements in developing and harmonizing building LCA standards (e.g., ISO 21931 [29] for LCA principles and framework for assessment of environmental performance of construction works, EN15897 [30] for the assessment of environmental performance of buildings, and the national Norwegian standard NS 3720 [31]), and in LCA results communication methods (e.g., EPDs, and green building rating systems such as BREEAM) and international research activities (such as the International Energy Agency's Energy in Building and Communities program (IEA EBC) Annex 57 [32], Annex 72 [33]) on assessing and communicating life cycle-related impacts of buildings. Life cycle-based national GHG emission benchmarks or reference values are receiving more attention in different countries, and there are on-going discussions on the possibility of legal bindings [34]. The lack of harmonized background data and methodology choices used in different studies is considered as a major challenge in the utilization of LCA studies to establish benchmarks [34; 35; 36]. Most existing benchmarks also provide aggregated values for both new and existing buildings, mainly due to a lack of LCA studies from existing buildings and heritage buildings. As with other Nordic countries, in Norway, there is no specific legal requirements for building LCA in the national legislation yet [37]. However, public building owners (e.g., the Norwegian government agency for administration of public buildings in Norway, Stastbygg), large municipalities (e.g., Oslo), initiatives, and projects (e.g., Futurebuilt, FME ZEB, FME ZEN) have been actively promoting the use of building LCA in Norwegian buildings for the past 15 years [37; 38]. Stricter legislation towards the implementation of energy efficiency measures and decarbonization of national energy mixes (through use of renewable energy sources) leads to a reduction in operational energy use [39]. However, these measures also increase the embodied emissions from: the initial embodied emissions (from manufacturing (A1-A3 life cycle stages)), transport to construction site (A4), construction installation activities (A5), recurrent embodied emissions (from use phase activities, B1-B5), and end of life embodied emission (C1-C4) (Figure 1). Most existing studies mainly cover the production (A1-A3), replacement (B4), and operational energy use phases (B6) [40; 41; 42]. The embodied impacts from the transport (A4), construction installation (A5), and end of life (C1-C4) phases are often considered  
Figure 1: System boundaries in building LCA in relation to life cycle stages, modules, and types of impacts (embodied and operational). Adopted from EN 15978 [30] and [PERSON] et al. [40]. as low, and those life cycle stages are either excluded or calculated based on very rough assumptions. However, on-going fossil-free, emission-free, waste-free, reuse of building products, and other circular economy activities show the importance of those phases. For example, the GHG emission from construction site activities is estimated to be 5-10% [43]. A recent report from Bellona estimated that construction-related transport accounts for 1% of Norway's total emissions [44]. The report also shows a potential GHG emission reduction by up to 50% by efficient transport of goods to and from Norwegian construction sites through better planning and higher utilization of the vehicle capacity. Adding the impacts from the construction use phase (B2-B5) and end of life stages can help to demonstrate the significance of the emission reduction potential from refurbishment of existing buildings.