**2. Retrofitting existing buildings vs. building new buildings**

Given the context of climate emergency and the pivotal role that the building industry must play in reducing carbon emissions, the question is whether to focus on retrofitting existing buildings or tearing down existing buildings and building new net-zero buildings? Retrofitting existing buildings could offer an excellent opportunity for reducing our carbon emissions at a faster pace. The low rate—1% per year of building demolition and rebuilding in most parts of the world [9] and the fact that almost two-thirds of the existing global building stock will still constitute buildings that exist today are reasons enough to opt for the retrofitting path. Not attending to this significant building stock would imply continual carbon emission even in 2040, resulting in a failure in achieving the 1.5°C target set forth via the Paris agreement. The 2021 Pritzker Architecture prize laureates Anne Lacaton and Jean

Phillipe Vassal echo this view of retrofitting via their unique approach to building a smarter, greener, and inclusive built environment—never demolish, remove or replace, always add, transform, and re-use [10]. Countries like Australia, with almost eight million homes constructed from the 1950s onwards (like buildings elsewhere in the developed and the developing world), were built during a time with far less stringent regulations around energy and building standards, insulation, and material quality. This resulted in buildings either on the verge of collapse, being poorly designed, containing hazardous materials (such as asbestos), or consuming high amounts of energy to maintain comfort levels for their inhabitants. In the Australian context alone, buildings are associated with 18% GHG emissions and 20% final energy use (COAG Council report) [11]. According to an editorial published in The Guardian, the United Kingdom's trend to demolish 50,000 buildings per year to construct new ones is responsible for two-thirds of the total waste production of the entire country. The construction of new buildings is additionally associated with 10% of the UK's carbon emissions [12]. In the United States, almost seven million buildings are estimated to undertake remodeling and renovations in addition to commercial buildings undertaking capital improvements [13]. Such large-scale building alterations offer an excellent opportunity to include energy performance enhancements while conducting renovations one architectural element at a time (wall, roof, windows, floors, etc.)—Opportunistic Retrofitting. It is projected that three measures—re-siding, window replacement, and re-roofing, can cut result in 25% more energy savings alone. Bloomberg presents an easy to comprehend comparison for how much impact this 25% reduction will entail. Suppose this 25% energy saving potential is harnessed by even 1% of the US's 83 million existing single-family homes. In that case, it will reduce carbon emissions by more than 1.6 million metric tons yearly, which is equivalent to removing 350,000 passenger cars from highways. Besides savings on energy bills worth \$400 billion each year, this positive environmental impact provides compelling arguments to transition to a nearly zero carbon building practice.

Besides this, it is essential to note that refurbishing and restoring existing buildings result in saving the embodied carbon footprint of the material used while constructing these buildings. This saving results in negating costs for mining, manufacturing, shipping, etc., of new materials that would otherwise be used for new constructions. In the long run, retrofitting thus becomes cost-effective with respect to CO2 rather than building new. However, what is also vital to consider is the positioning of the building sector within the bigger landscape of energy and climate change debates. Retrofitting on its own, though beneficial, would benefit immensely if it harnesses an energy upgrade involving the following: Incorporating improvements in the energy efficiency of building operations; embracing a shift from fossil fuel to electric or district heating that is backed by carbon-free renewable energy generation practices; generation of carbon-free renewable energy on-site.

Within the current context of popular media exploding with discussions around climate emergencies and the need to reduce our carbon footprint and associated emissions, awareness about harnessing renewable energy has strengthened within the general population. However, what does it truly mean to become carbon neutral or, for that matter, what does a zero carbon badge imply for the building sector? The next section of this chapter engages in a short discussion around the concept of zero carbon to base tools and techniques that can be instrumental for reaching a zero carbon or a net zero retrofitting strategy.
