As an innovative, forward thinking builder, BCCI strives to understand and identify issues that clients know are important to their buildings. The New Carbon Architecture, with its comprehensive analysis on embodied carbon issues, is an excellent reference point to access a new frontier of climate-related building strategy. Our team is seeing the issue of embodied carbon occupying a larger space in local and national markets, and wants to promote that issue and be a leader on the cutting edge of this movement.
A book made of carbon, written by carbon, for carbon, on how to build carbon shelter to protect us from a sometimes hostile carbon planet. Shall we dance? – Bruce King, Lead Author of The New Carbon Architecture
The New Carbon Architecture (TNCA), written by lauded green building practitioners like Bruce King, Ann Edminster, Frances Yang, Mikhail Davis and Massey Burke, is one of the most unique green building books to hit the shelves in years. TNCA is the importance of embodied carbon in buildings and actionable methods to reduce the industry’s carbon impacts. The building industry has enormous potential to impact the emission reduction goals set by the United Nations Framework Convention on Climate Change Paris Agreement. According to the Intergovernmental Panel on Climate Change (IPCC), all building [carbon] emissions need to be reduced 80 to 90 percent by 2050, new construction must be fossil-free and near net zero energy by 2020, and the rate of energy rehabilitation for existing buildings will need to increase to 5 percent per year in developed countries. The authors focus on four materials: cement, wood, straw and plastic to explain considerations in embodied carbon contributions to our built environment.
陶汉林What is embodied carbon?陶汉林
Embodied carbon includes all of the greenhouse gas emissions related to the production of the materials ordered for the construction of a building, as well as the process of construction itself. As soon as a building is finished and occupancy begins, the energy it takes to operate the building is included in the operational carbon, typically targeted by energy efficiency, carbon offsets and on-site renewable energy. In total, embodied carbon accounts for an average of 20% of a building’s total energy consumption over its life. Considering the new construction projects projected to happen between now and 2050, 80-90 percent of the energy profile will be embodied, not operational. This creates a strong imperative for taking a serious look at the embodied carbon in our building materials.
Many of the world’s oldest buildings were built out of essentially the world’s first concrete- sundried mud and clay bricks. Clay, the original binder, has been used since the first settlements of Mesopotamia in the Fertile Crescent 9,000 years ago. The modern city of Shibam, Yemen still boasts ten story sky-scrapers made of sunbaked mud.
In the early 19th century, the invention of Portland Cement (PC) forever changed the future of building. This new concrete binder was discovered by heating and grinding limestone at previously unattempted temperatures- over 14,000 degrees Fahrenheit. The result creates a compressive strength that is ten times that of an unfired clay brick, over 3000lbs per square inch.
While durable, however, PC affords us challenges that warrant a need for alternatives based on two major factors: supply and environmental impact. PC is a mixture of sand and limestone- both of which are facing supply shortages when production numbers are projected against population growth and demand. The other issue is carbon intensity. Currently, the production of PC accounts for 6% of global carbon emissions.
Other materials can replace cement, but none can be produced at capacity for the design and construction market. Some efforts are focused on improving/inventing new cements with smaller carbon footprints, inventing carbon storing artificial sand and gravel and storing carbon in PC. In some cases, PC is being added to natural clay for additional strength. While concrete alternatives aren’t all so common these days, we’re expecting more availability in the near future. Watershed Materials’ concrete blocks use up to 50%less PC and a 65% reduction in embodied energy compared to conventional concrete. These bricks have been used for ambitious residential projects, like the Napa Residence by Atelier. Blue Planet’s concrete mix captures carbon during the manufacturing process, and has been applied at Interim Boarding Area B at the San Francisco International Airport.
Carbon sequestration is the process by which atmospheric carbon dioxide is taken up by trees, grasses, and other plants through photosynthesis and stored as carbon in biomass (trunks, branches, foliage, and roots) and soils. The sink of carbon sequestration in forests and wood products helps to offset sources of carbon dioxide to the atmosphere, such as deforestation, forest fires, and fossil fuel emissions.
Sustainable forestry practices can increase the ability of forests to sequester atmospheric carbon while enhancing other ecosystem services, such as improved soil and water quality. Planting new trees and improving forest health through thinning and prescribed burning are some of the ways to increase forest carbon in the long run. Harvesting and regenerating forests can also result in net carbon sequestration in wood products and new forest growth.
In response to government, business, and individual commitments to reduce carbon dioxide emissions, carbon is now a priced environmental commodity in the global marketplace. The United States carbon market is in its formative stages.
Cross-laminated Timber (CLT) was invented in 1998 and offers a much stronger form of construction using solid timber panels rather than lightweight cassettes. With CLT, boards are laminated in alternating directions (which is why some people call it “jumbo plywood”), creating panels that are stronger and stiffer than stick-framed systems. CLT panels are considered to be heavy or “mass” timber, meaning they have some inherent fire resistance and the ability to be used confidently at scale.
“There are other carbon-capturing “forests” that have so far escaped much attention – the vast miniature forests where we grow our food.”
In 2014 over 720M hectares of grains were grown globally, roughly the size of Australia. The stalk beneath every grain seed is a very unassuming natural building material. This material is straw, which contains about 35-60 percent of its mass as carbon. It is also lightweight, abundant and has strong, tubular stems.
This natural building material’s promising characteristics make it a prime candidate for low carbon architecture and carbon sequestration. Natural materials like straw bales actually process atmospheric carbon during photosynthesis and have astounding CO2 sequestration rates compared to conventional materials like fiberglass batts, mineral wool batts and polystyrene foam (see table below). Straw is also much easier to grow than a forest – this ecosystem is already functioning as a CO2 bio-absorption system.
While agriculture emits a vast amount of carbon, one solution is to embed the sequestration process in natural building materials used in the construction process.
This material has been used in thousands of buildings and at least 50 countries around the world. And the material has evolved into various standardized building products such as:
? Straw bales and bale panels
? Straw blocks
? Straw panels
? Plant fiber insulation systems
It’s even just as cost effective as conventional construction materials and has good load-bearing capacity, while its insulation properties boast an impressive R2 per inch.
However, its adoption to market has been difficult. Incorporating the above materials into commercial construction requires builders to “rethink their supply chains, retrain workers, and redesign the basic framing system used in conventional construction”. This material has been best suited for residential construction and owners who are truly committed to natural building materials, high carbon sequestration and the lowest operational carbon footprint.
Plastic has been one of the great inventions of the last century. It can be used in so many applications and is strong yet malleable, can be created easily, and lasts forever. The many different types of plastics serve many different purposes, but there are two main types of plastics: plastic made from petrochemicals and those made from plant biopolymers.
Petrochemical plastic has been the most durable plastic made and has been the most commonly produced to date. These industrial plastics like polypropylene and polyethylene are created from non-biological sources of carbon. While petrochemical plastic is the most durable and inexpensive to make, it is using a non-biogenic carbon in its production. In addition, its production releases a vast amount of harmful chemicals into the air, soil and water.
Bio-based plastics come from taking materials from plants, animals, and even bacteria to make various different biopolymers. The production of these plastics such as polylactic acid (PLA) are derived from biological sources of carbon. Alone, these biopolymers create plastics that are used in items like biodegradable packaging and compostable dishware and utensils. In order to make these bio-based plastics more durable and to rival petroleum-based products, they need to be mixed with other chemicals, making the recycling or decomposition much more complicated.
While plastic is a great option for an easily manufactured product to use in our buildings, we need to shift our relationship with plastic, especially single use plastics (40% of all plastics in landfill are from packaging). While packaging is the largest source of plastic use globally, the second is the building sector. What can we do to make more informed decisions on what plastics to use in our built environment? The issue comes down to reuse and recycling. The tricky thing with plastic is that there are too many different combinations of polymers that make up a plastic that it is often impossible to determine the exact chemical makeup in order to properly recycle. We need to determine a better way to make plastic last over multiple recycling and repurposing uses. The building industry is beginning to demand ingredient transparency as well as evaluating environmental life cycle impacts of products before procuring and installing them on projects. This is the right step in the direction of closing the loop on plastics.
Our Sustainability Director, Kena David, represents BCCI in the Sustainability in Construction Leaders (SCL) group that started over a year ago at Greenbuild 2017. The SCL group has been focused on a number of initiatives to drive general contractors towards sustainable practices independent of green building certifications. One of the initiatives of the SCL is to start looking at the embodied carbon in our projects and identifying better materials with a lower carbon impact to produce a lower carbon project. Empowering project teams with the decision to choose materials based on carbon impact will change the way we think about materials from structural foundations all the way to the finishes we see in our offices.