Many homes are demolished each year to make space for new construction. The need for new infrastructure and modern housing meets developers and investors who find it more profitable to replace existing homes with new ones that command higher prices or rents. Modernization and the desire for updated amenities and energy savings also play their roles.
Unfortunately, those demolished homes are often far from the end of their useable lifespans. So a lot of construction materials, appliances, and interior finishes end up wasted in landfills. Those materials decompose slowly, releasing methane and other harmful gases. Plus a houseful of new products will need to be manufactured from scratch in order to rebuild, increasing embodied carbon.
The role of deconstruction
Over the past decades, energy efficiency has been the focus of green home policies; for good reason. The amount of energy required to heat our homes was historically high because buildings were not energy efficient. If those homes rely on high-carbon fuel sources, then the associated greenhouse gas emissions (called operational carbon) are also very high. But building codes today require more insulation and airtight construction. And energy sources around the globe are increasingly decarbonized with renewables. This results in homes that now release minimal operational emissions.
At the same time, we’ve added new materials and technology (i.e., more insulation, triple-glazed windows, etc.) to reach these energy efficiency targets. Thus, embodied carbon accounts for an increasing portion of a high-performance home’s total emissions. Here lie valuable opportunities to further decrease overall emissions from the building sector.
One of the solutions to reduce embodied carbon is an alternative to demolition: deconstruction (also known as sustainable demolition). This approach is an orderly disassembly process, preserving building materials in the hope of reusing them. Thereby reducing waste and minimizing environmental impacts. By reusing materials instead of manufacturing new ones, we can significantly reduce embodied carbon and promote a more circular economy.
Understanding embodied carbon
Embodied carbon, also referred to as embodied emissions, comprise the greenhouse gases emitted during the extraction, manufacturing, transportation, installation, and disposal of building materials. The relationship between embodied and operational emissions is complex and must be calculated over time in a life cycle analysis. Operational carbon comes from the energy used to heat, cool, and power buildings. Therefore, operational carbon savings comes in small amounts over the whole lifespan of a building. In contrast, embodied carbon is “locked in” once the building materials are produced and transported. The vast majority (70%–90%) of embodied carbon is released in the relatively short time from materials extraction and production to when the homeowners take up residence.
Embodied emission were 7.9 tonnes CO2e lower when the modeled home was partially deconstructed and renovated.
Does it matter if it’s new or retrofitted?
When it comes to achieving a high energy efficiency target, is retrofitting or building new the best option? Our team at Carbon Wise worked on a case study to quantify the emissions associated with both scenarios. The North Vancouver net-zero retrofit project provides a compelling example of how deconstruction and reuse of materials on-site can yield both financial savings and reductions in greenhouse gas emissions. Modeling and life cycle assessments showed that the deep energy retrofit scenario had significantly lower embodied carbon compared to a new build scenario.
In the retrofit scenario, the existing foundations were kept; thus eliminating the need for new concrete. Concrete is usually the top emitter in new construction, so in this case we saved approximately 8 metric tons of CO2 emitted. The retrofit scenario provided an efficient, comfortable home, nearly identical to new. The roof and solar panels, electrical and mechanical systems, and plumbing are all the same; as are finishes, fixtures, and landscaping. However, the existing slab remains uninsulated, and ceiling heights are slightly lower.
By reusing existing structural elements and cladding, the retrofit avoided the emissions that come with making those new materials. Both the retrofit and the new build scenario needed solar panels along with upgrades to windows and insulation to hit energy efficiency goals. Low-carbon materials (having 40%–80% less embodied carbon) and thoughtful design ensure that the carbon invested in the retrofit will be paid back swiftly through lower operating emissions: in less than 5 years.
Deconstruction: implementation and practice
Repurposing materials like wood, metal, and concrete through deconstruction significantly diverts waste from landfills. It is also in line with circular economy principles of reusing or recycling resources. Salvaging means materials are not needlessly discarded, and can be reused in new projects. For example, reclaimed wood can be repurposed into non-structural elements, flooring, or finishes. This saves natural resources and offsets the impact of entirely new production. Deconstruction also creates jobs in the recycling and material reuse sectors. Second-hand and salvage stores are good for local economic development.
Successful deconstruction requires careful planning and execution. The first step is to evaluate the structural integrity of the building to determine what is safe and retrievable. This evaluation informs the deconstruction plan. It’s always important to work in collaboration with the design and build team, alongside the energy and carbon consultant, to make the most of the materials to be reused either directly on-site or in another project.
Embodied emissions modeled in four scenarios.
Deconstruction is one of the easiest (and maybe cheapest!) solutions for reducing embodied emissions in the construction industry. By prioritizing the reuse of materials, we can significantly lower the carbon footprint of building projects and achieve financial savings. As the industry moves towards net-zero and low-carbon goals, integrating deconstruction practices will become essential. Deconstruction addresses the urgent need to reduce embodied carbon, and at the same time supports waste minimization, resource efficiency, and local economic growth.
The author:
Elisabeth Baudinaud is Founder and Principal of Carbon Wise. She is an experienced leader in policy development and community resiliency, with a dedication to advancing low-carbon construction practices. Carbon Wise serves as a bridge between the realities of on-the-ground construction and the imperative to meet climate targets.
Baudinaud collaborated closely with over 20 local governments, the Step Code Council, and the Province of British Columbia, in the implementation of the BC Energy Step Code and Zero Carbon Step Code. She volunteers with the Carbon Leadership Forum – BC Hub and serves on the educational committee of the Homebuilders Association of Vancouver.
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Ted Reiff says:
The entire industry spends more time on carbon (which in many cases is a very useful element – think of carbon chains. While you addressed embodied energy and explained it quite well, the majority of people relate to the word energy more than they do carbon. My suggestion is to emphasize embodied energy with examples and do away with carbon unless it is used in technical papers. Further embodied energy is easier to measure than carbon.