Net-Positive Carbon Design and Materials
Updated: Sep 2, 2021
A core value of AGD is providing a net-positive impact through our work. Impactful design can mean designs that promote emotional change through their aesthetics, positive change in healing the environment, social change in a community, and much more. We do not strive for meeting a standard of being impactful in our work but rather how our lives and examples of living can impact others. A building can have a net-positive impact environmentally through functions such as producing usable energy, storing excess carbon dioxide (CO2), and featuring sustainable materials that help mitigate climate change.
With nearly 40% of global CO2 emissions stemming from the building sector, we have a responsibility as designers to shape the built environment in a way that prioritizes long-term sustainability. In order to curb climate change, the Paris Climate Agreement mandates an elimination of global greenhouse gas (GHG) emissions from the built environment by 2040, the most abundant of which is CO2 (accounting for 80% of GHGs). A building’s up-front embodied carbon content (from the harvesting, manufacture, and transportation of building materials), energy consumed, and fuel source emissions (from heating, cooling, and powering appliances) all contribute to CO2 output. CO2 in turn is removed from the atmosphere via photosynthesis and sequestration performed by trees and plants, but we are currently producing far too much CO2 on a global scale for these natural processes to help us maintain an equilibrium.
In its construction and daily usage, a home or other structure with a net-positive carbon impact would store more carbon than it releases into the atmosphere. First, it would have a minimal embodied carbon footprint by being made of materials that store carbon, while not releasing excessive amounts of CO2. Second, it would have a low operational carbon footprint; it would be designed with passive strategies (such as window shading, natural ventilation, etc. based on the local climate) so that ideally, A/C or heating needs are minimal or eliminated. The building would also be powered by a renewable energy source such as solar energy produced on-site, and it would be located near bike paths and public transportation while also offering electric vehicle charging powered by renewable energy.
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Research by the University of Cambridge suggests that designing buildings for the lowest material use rather than the lowest cost is a step in the right direction towards massive carbon savings. While cost will always serve as a constraint, especially in developing countries, many affordable and widely available materials do exist. According to Builders for Climate Change, responsible material selection provides the greatest impact at the individual building level, with a reduction of up-front emissions up to 150%. The suggested low embodied carbon materials here are realistic alternatives to other conventional materials, and their implementation requires no changes in building codes or construction methodology.
These suggested materials are largely plant-based or recycled, meaning that they are already serving as a carbon sink. In general, they are also in a form that is close to their natural state--an extensive, high CO2-producing manufacturing process is not involved like it is for materials such as conventional steel and concrete. It is important that all wood products used in construction are FSC-certified, and that all materials are locally-sourced as much as possible.
Because the energy required for heating and cooling has a massive impact on carbon emissions, it is important that buildings are adequately insulated with sustainable types of insulation. Where the local climate allows, it is recommended to specify blown-in (i.e. “loose fill”) insulation instead of petroleum-based rigid and spray foam insulations, including expanded polystyrene (EPS), extruded polystyrene (XPS), polyisocyanurate (polyiso), structurally insulated panel systems (SIPS) containing foam insulation, and spray foam; these insulation types are traditionally used because they are good at trapping (highly-insulating) air and they don’t easily absorb moisture, but they do have very high amounts of embodied carbon. Natural materials that both insulate and sequester carbon, such as straw, clay-straw, wood, hemp, cork, sheep’s wool, cellulose, and denim are ideal.
Two sustainable insulation options that are gaining traction include dense-pack cellulose (DP) and denim insulation. DP technically can be made of any organic material with a cellular structure (such as corn cobs and sisal), but is more commonly made from recycled paper, cardboard, and other waste products in commercially available options. Both insulation types can be safely handled without the installer having to wear extensive personal protective equipment, are non-toxic, and have not been associated with any health risks like fiberglass has. DP and denim insulation is made to be fire-resistant and deter pests, fungi, and bacteria. While mineral fibers in some conventional insulation types rely on air to insulate, organic fibers in both DP and denim can be packed tighter to provide both air sealing and insulation. In the case of a denim-insulated building needing to be deconstructed, the denim insulation can even be recycled again and used in another structure. Furthermore, insulation upgrades made to old buildings can drastically improve their performance, with the air leakage area typically reduced by 40-70% by, for instance, dense-packing between studs.
Almost two-thirds of the global building footprint that exists today will continue to exist through 2040--the end of the current Paris Climate Agreement timeline. This means that CO2 mitigation efforts cannot be focused solely on new construction, but also on updating/renovating existing structures, which makes up less than 1% of all construction at this time. In both new construction and renovations, it’s critical for designers and clients alike to push for the use of sustainable materials, helping in the effort to create a global building sector carbon footprint of net-zero, and ideally beyond to net-positive.
Written by Kristin Fauske and Hannah Oitzman