The concept of “decarbonization” has been in vogue recently in political speeches and global environmental events, but it has not yet gained enough attention in the field of architecture to profoundly change the way we design and construct the world of tomorrow. Buildings are currently responsible for 33% of global energy consumption and 39% of greenhouse gas emissions, indicating that architects must play a significant role if we are to stop or reverse climate change. With carbon acting as a universally agreed upon metric with which the greenhouse gas emissions of a building can be tracked , one of the most important ways through which this goal can be achieved is therefore the decarbonization of buildings.
Decarbonization encompasses the reduction of both operational carbon and embodied carbon, which refer to carbon emissions in the use stage and over the entire life cycle of a building respectively. This life cycle encapsulates extraction, transportation, installation, use, and end of life for every material and furnishing, and is responsible for 11% of global greenhouse gas emissions and 28% of global building sector emissions . Initiatives such as the Net Zero Carbon Buildings Commitment, which launched at the Global Climate Action Summit in 2018, promote the global reduction of operational carbon through calls to reduce the amount of carbon dioxide emissions released on an annual basis to zero or negative . Other initiatives, such as the U.S.’s Carbon Leadership Forum, emphasize the importance of decreasing embodied carbon as well, citing projections that the world’s building floorspace will double by 2060 as a sign of its importance .
To these ends, we outline ten strategies below to decarbonize architecture, ranging from important considerations, to procedures, to products and documents that could serve practical use for architects looking for concrete solutions.
1. Approach Decarbonization at Three Levels
Because different carbon reduction strategies model varying levels of effectiveness and different building stages require different procedures, the World Resources Institute presents a tier list of strategies ranked by priority that can be roughly transformed into three procedures of decarbonization. The WRI list for the reduction of operational emissions proceeds as follows: energy efficiency before renewable energy; on-site renewable energy before off-site renewable energy; and renewable energy before carbon offset (investing in renewable energy elsewhere). For embodied emissions, it suggests carbon reduction again before carbon offset. This method of carbon offsetting is consistently low priority because it is only recommended for cases where a 100% renewable energy supply is not feasible . With this hierarchy of priorities, we can therefore approach the decarbonization of buildings at three different levels:
1) The reduction of operational carbon in existing buildings through energy efficiency;
2) Use renewable energy to cover the remaining low energy demand, ideally on site or offsite nearby if necessary;
3) Reduce the embodied carbon of new buildings over their entire life cycle.
These levels are not a cohesive procedure with which architects should approach decarbonization – i.e., embodied carbon reduction comes last – but simply encapsulate three different ways that architects can reduce carbon emissions, depending on the stage or requirements of the building. Ultimately, all three must be achieved rapidly to meet the Paris Climate Agreement targets. Distinguishing these three levels simply serves as a helpful guide with which architects and building owners can approach decarbonization vis-à-vis their own projects.
2. Consider Operational and Embodied Carbon Together
As discussed above, the reductions of both operational and embodied carbon are necessary steps in the decarbonization of architecture as a whole. Yet for existing buildings, because materials are already in place, embodied carbon may be less of an essential consideration and building owners should prioritize reaching net zero operational carbon. In contrast, in the construction of new buildings – the responsibility of architects – considering only one type of carbon emission or the other can provide misleading results about the true environmental impact of a structure. For example, the use of some materials can yield low operational carbon output but high embodied carbon over its entire life cycle, and vice versa. A building with little insulation and single glazing will typically have lower embodied carbon, but increased operational carbon compared to a well-insulated building. Likewise, while equipment to produce renewable energy can reduce operational carbon significantly, architects must remember that the manufacture of such equipment leaves a carbon footprint itself. Because of these potential inconsistencies, it is essential that architects of new buildings or significant renovations consider both types of carbon output simultaneously when choosing materials to optimize energy efficiency and leave the lowest carbon footprint possible.
3. Target the Early Phase of the Project
To do so, architects should approach decarbonization with rigor and detail immediately at the outset of a new project. Low carbon design practices, especially those that target embodied carbon, are both most efficient and most cost-effective when considered in the early phases of a project . One Click LCA’s Embodied Carbon Review outlines the reasons for this higher efficiency in detail. The early phases of a project “lock in” the possibilities for many parts of a design, including those that could significantly affect embodied carbon emissions. Architects may be unable to make energy efficient changes later, or the range of possibilities will be severely truncated. For example, choosing a site requiring very deep foundations can more than double a project’s embodied carbon emissions, yet architects cannot amend this choice later on. Less drastically, as time goes on even if an element can still be changed it will almost always incur drastically higher costs. It is therefore imperative that architects analyze possibilities for reducing embodied carbon early on in the design process.
4. Utilize Lightweight Materials
One way that architects can achieve this goal is through the use of lightweight materials. In a study conducted by Saint-Gobain comparing two internal wall profiles commonly used in Brazil, they found that the lighter weight system yielded a host of environmental benefits . The lighter option was the Placo drywall system, an insulated metal stud drywall, which was compared to a cement plastered 140 mm brick traditional wall system. For one square meter of partition walls, they found that using this drywall system in place of the traditional wall would cause a 63% reduction in global warming potential, a 49% reduction in primary energy use, an 80% reduction in wall system weight, and a 36% reduction in fresh water usage. Similarly, a lightweight external wall system called Façade F4 was found to halve the CO2 emissions of a traditional massive façade. These products not only demonstrate the effectiveness of lightweight wall systems but provide tangible feasible options for architects looking for environmentally friendly solutions.
5. Consider Biosourced Materials
Similarly, some biosourced materials such as wood, hempwool, and wood fibers store carbon over their use stage, meaning they actually reduce carbon dioxide levels in the atmosphere prior to the disposal of the material and remission of the carbon. This quality makes them a highly effective and sustainable material. Nevertheless, architects considering this option should be aware that in the new EN15804-A2 Life Cycle Assessment standard (discussed in part 8), this stored carbon – called biogenic carbon, during plant growth – must be accounted separately from embodied carbon (extraction, transportation, installation, use, end of life) due to important categorical differences. For example, the embodied carbon of a biosourced material may be higher than that of traditional materials due to a greater distance from the construction site, and the biogenic carbon itself has a net emission of zero over its entire lifetime because of the uptake and eventual re-emission of carbon. By the new LCA standard, biogenic carbon is therefore accounted as separate and zeroed-out over the whole lifecycle – i.e., it is no longer considered as leaving a negative carbon footprint.
6. Acknowledge Interior Elements as Potential Carbon Emitters
A common mistake made by designers in the early stages of planning is to account for the core and shell of a building when calculating embodied carbon, but forget potentially significant interior fittings, mechanicals, and technical equipment. That these objects have a shorter lifetime and might be replaced many times over the building’s life makes their embodied carbon output as important as that of any other part of the structure. Only by accounting for these important interior elements will the calculated embodied carbon be at all accurate.
7. Reuse or Recycle Existing Materials
Reusing existing materials eliminates the need to extract and manufacture new materials at potentially high environmental costs. If feasible, architects should try to purchase products that use as much recycled material as possible to lower embodied carbon quantities. In glazing, for example, glass made of cullet – reused and therefore decarbonated waste glass – can decrease energy use by 3% for every 10% of cullet used. Likewise, using one ton of cullet reduces CO2 emissions by 300 kg due to the decreased energy consumption. Thus, glazing made of cullet and other examples of recycled materials should be a strong consideration for architects working toward decarbonization.
8. Use Life Cycle Assessments or Third Party Verified EPD’s
Architects can evaluate the carbon output of their buildings through Life Cycle Assessments (LCAs) set by international standards and through results published in third party verified Environmental Product Declarations (EPDs). These are the only valid scientific sources of information for the embodied carbon of construction products and materials. LCAs are a cradle-to-gate or cradle-to-grave analysis technique that evaluates the environmental impacts of all stages of a product’s life . EPDs are independently verified and registered documents that communicate “transparent and comparable” information about the environmental impact of a product throughout its entire life cycle . Architects can use both to determine and evaluate the carbon footprint of their designed structure. To standardize the ways in which products are evaluated, EPDs and the life cycle assessments that can be drawn from them are regulated by international standards such as European standards. One particularly relevant example is EN 15804, which provides core product category rules (PCRs) for the environmental declarations of construction products and services. Because of its relevance to the construction industry, EN 15804 is an important standard for architects specially to know and respond to.
Many different software applications exist that can automatically provide Life Cycle Assessments from design data and offer optimal solutions. One prominent example is One Click LCA, which draws from Revit, IFC (BIM), Excel, IESVE, energy models (gbXML), and other tools to find comparable solutions and offer pertinent materials with accessible EPDs. Architects serious about decarbonization should use this tool or similar applications to ensure that their embodied carbon output is as low as possible.
9. Bring Buildings Into the Circular Economy
Pertinent to the question of life cycle assessment is the disposal or reuse of products after their useful life. The cessation of the ‘take, make, and waste’ model toward a circular economy of resource efficiency is an imperative measure to take to achieve a more sustainable building industry . A building adhering to the guidelines of circular economy will naturally consume fewer resources over its life cycle because it is designed to be resource efficient, adaptable, and long-lasting. Within this building, as stated above, most constitutive materials with an increased percentage of recycled content will output a reduced carbon footprint. Reused materials and products will emit a lower quantity of embodied carbon as well. All of these solutions are examples of circular economy, demonstrating its utmost importance to the decarbonization of architecture. The buildings sector accounts for approximately half of all extracted materials and one third of waste generation in all of Europe . Eliminating the negative impacts of extraction and waste through reuse and recycling in our industry could therefore be enormously impactful in the global effort to end global warming.
10. Support Global Initiatives
While these strategies all constitute extremely important individual solutions, the path to decarbonize must be a global collective effort for results to show. Firms can aid in advocacy and awareness by supporting global and local initiatives such as the Net Zero Carbon Buildings Commitment, the Global Alliance for Buildings and Construction, the Carbon Leadership Forum, and more.
The World Green Building Council’s 2019 embodied carbon call to action report details a plan to reach zero operational carbon and 40% less embodied carbon for all new buildings by 2030, and zero embodied and operational carbon for all new and existing buildings by 2050 . This plan was developed explicitly to help deliver on the ambitions of the Paris Agreement and keep global average temperature rise well below 2 degrees Celsius. However, these targets remain lofty goals as new buildings continue to be built at a rapid rate, with the equivalent of Paris’ area added in floor space every five days and half of the buildings in 2060 having not been built yet . For the World GBC plan and the Paris Agreement to succeed against these odds, architects must come together to lower carbon emissions in the building industry as a whole. Embodied carbon, operational carbon, existing buildings, new buildings, circular economy, lightweight or biosourced materials, recycling, and more must all be considered to approach decarbonization holistically. With the ten strategies delineated above, we hope to do our part to help.
-  The Net Zero Carbon Buildings Commitment
-  Carbon Leadership Forum Resource Library
-  Zero Carbon Buildings for All / WRI Ross Center for Sustainable Cities
-  Embodied Carbon Review / Bionova (2018)
-  Environmental Benefits of Drywall, compared to brick or block wall system / Placo - Saint Gobain
-  Life Cycle Assessment / Science Direct
-  What is an Environmental Product Declaration (EPD)? / EPD International AB
-  Building Sustainability Performance - Level(s) / European Comission
-  Bringing Embodied Carbon Upfront / The World Green Building Council (WorldGBC)
-  Why Buildings? Our Key Messages / UN Environment Programme