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             A net zero status is popularly   in embodied emissions of the building   depreciation, and residual costs.
             understood as the gold standard in   (Adams, Burrows, and Richardson   Similarly, a life cycle carbon analysis
             building energy efficiency. In typical   2019; Graham 2019; Schmidt,   needs to include upfront carbon,
             situations, a building achieves this   Crawford, and Warren-myers 2020).   annual emissions, and end-of-life
             status based on an annual balance   The annual performance evaluations   processes. An LCA for a building
             sheet of electricity. This balance   do not consider the embodied   requires the use of a metric that
             sheet presents an environmental   carbon released before the use of   applies to all the phases of a building’s
             evaluation for the building, annually,   the building. With these additional   lifespan. This metric must account
             in terms of its Energy Performance   provisions, the embodied emissions   for GHG emissions,  typically
             Index (EPI). The key performance   of a net zero building can be higher   measured in terms of equivalent
             indicator is the annual consumption   than those of a typical building. The   carbon dioxide (CO e). The metric
             (EPI) with respect to the on-site   annual savings may or may not be able   should quantify the emissions from
             generation (net-EPI). It is typically   to compensate for these additional   various GHGs based on their global
             measured in kilowatt-hour (kWh)   emissions, even across the lifespan   warming potential (GWP). Once
             and expressed as a function of the   of the building. For the building   the impact is quantified in terms of
             building area (kWh/m /yr). The   industry, a positive net-EPI is not   CO2e, it can be normalized for the
             common use of this metric is based   good enough to ensure a significant   factors of time, area, occupants,
             on the idea that annual savings in   reduction in emissions anymore. It is   and cost. This normalized value can
             electricity translate to reduction in   now necessary to be able to quantify   be used for comparative studies or
             greenhouse gas (GHG) emissions.   the total impact of a building on the   benchmarking (Parkin, Herrera, and
             However, recent research has    environment across its life cycle.  Coley 2020; Ürge-Vorsatz, Khosla,
             suggested that may not be the case                             Bernhardt, et al. 2020).
             (Bordass 2020).                 The total impact can be quantified   Embodied carbon is projected to
                                             through a life cycle analysis (LCA).   account for 50% of the total carbon
             A net zero status is achieved through   When typically conducted for   footprint of new construction
             the provision of elements such as   economic costs, an LCCA (life cycle   until 2050 (Adams, Burrows, and
             insulation, high-performance glazing,   cost analysis) not only considers   Richardson 2019). Data on embodied
             on-site photovoltaics, etc. The   the annual net sum but also looks   carbon can be sourced from life cycle
             provision of these systems increases   at initial investments, inflation,   databases and environmental product
                                                                            declarations (EPDs) based on their
                                                                            applicability to the project’s geography
                                                                            and time. Contextualizing the data
                                                                            sets for each project is necessary to
                                                                            come close to the true impact. The
                                                                            share of these emissions in the total life
                                                                            of a building can vary so much that it is
                                                                            not feasible to draw a simple, broadly
                                                                            valid conclusion. The variations in
                                                                            these shares are primarily due to
                                                                            differences in construction materials
                                                                            and technologies.

                                                                            1    GHG emissions in buildings are typically
                                                                              indirect, occurring due to the use of
                                                                              electricity in the building. Absolute
                                                                              emission numbers, therefore, largely depend
                                                                              on emission factors considered during
                                                                              calculation (Lucon, Ürge-Vorsatz, Ahmed,
                                                                              et al. 2014). There is a need to include gases
                                                                              other than CO  because some construction
                                                                              products and HVAC equipment emit
                                                                              substantial amounts of GHGs, such as
                                                                              methane, nitrous oxides, and HFCs.
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