Low-carbon building materials: Designers discuss alternative options
November 22, 2023
From structural hemp to biobased cements, designers are excited about options to reduce embodied carbon
A version of this blog first appeared as ¡°Living in a material world¡± in Design Quarterly Issue 19.
If the building industry is going to take on climate change in a real way, we need to talk about materials. Low-carbon building materials. The embodied carbon¡ªthe greenhouse gas emissions¡ªrequired to make our built environment is associated with concrete, steel, and other carbon-intensive building materials.
What are the alternatives? We asked our designers and engineers what materials excite them.
Hemp insulation for sequestered carbon
Status: Available now
Sheep¡¯s wool, a natural low carbon insulating material, is particularly good at addressing moisture. It can get wet and then dry out, and it doesn¡¯t settle or lose its shape over time. However, there are other lower carbon content options. Cellulose fiber insulation comes from wood waste or paper waste. This, in theory, gives it the largest negative carbon footprint. It is also the cheapest and most easily blown in; but it does settle if not installed to the correct density. Hemp insulation is another negative-carbon material. You can get it in it all kinds of insulating and structural forms.
The Bunker Hill Housing Redevelopment in Boston, Massachusetts, has a focus on energy efficiency and resiliency. Designs for the first two buildings include mass timber.
Structural hemp also has great promise. You grow the hemp, harvest the material, then compress it. They use mushroom glue to put the hemp pieces together. It only takes 8 months instead of 25 years to grow the same amount of structural material as a well-managed Forest Stewardship Council forest, and the hemp sequesters many times more carbon. Structural material, board materials, insulating batt material, and insulating loose fill materials¡ªyou can get all of these from hemp. There are factories for hemp insulation in Quebec, Alberta, and the US.
With mass timber, carbon-negative buildings are possible (Brett Lambert)
Status: Available now
Most large buildings designed and built today use concrete or a composite steel and concrete as their structure. Concrete and steel are the materials of choice and have been for decades. But they are major contributors to embodied carbon in a building.
The volume of these carbon-intensive structural components makes up a large part of the overall building. So, it makes sense to look at alternatives with lower carbon intensity. Some good options include mass timber, CLT (cross-laminated timber), glulam, and engineered wood products.
The evolution of building codes allows us to use mass timber to build taller than we have previously. The key to mass timber is to harvest it sustainably; so, we must look for a company that is managing their forests appropriately and not clear cutting.
Atlassian Central in Sydney, Australia, will be the world¡¯s tallest commercial hybrid timber tower. Â鶹´«Ã½ is providing mechanical, electrical, hydraulic, security, and acoustic engineering; fire services; and lighting, ICT/AV, and vertical transport design. (Architect of Record: Shop Architects and BVN Architects)
The benefit is that when you¡¯re using wood, it has already pulled carbon out of the environment. It¡¯s therefore possible for us to target carbon neutral or even carbon negative on the structure if done right. Mass timber also creates a lighter structure. This means you can reduce the size of foundations, which can help decrease the amount of concrete and steel in the foundation and potentially reduce the how much excavation takes place.
Mass timber has many benefits even outside of embodied carbon. We can expose it and celebrate it in the design of the building and get the benefits of biophilic design. People have a natural connection to wood.
Right now, we are sourcing the mass timber and CLT for the projects we¡¯ve designed in the Boston area from the West Coast, primarily from British Columbia, Canada. But there¡¯s talk of converting mills in the Northeast to produce mass timber to meet the demand locally.
The evolution of building codes allows us to use mass timber to build taller than we have previously. The key to mass timber is to harvest it sustainably.
Mushrooms and biobased cement are part of the low-carbon building materials future (Jill Dexter)
Status: Available now
MushLume lighting is made from mycelium fiber that¡¯s combined with sustainably sourced hemp. The mycelium grows quickly to create different shapes for the light fixture housing. Rather than using a plastic or resin for the housing, it uses a plant-based material. And it becomes durable enough that it can handle paint, which provides some fun colors. It also has a unique celestial look.
I can see these fixtures working great in hotels, restaurants, bars, common areas in multifamily residential spaces, or the workplace. Maybe you¡¯d want to include a fixture or two in a new yoga studio or another place intended to be a little bit more serene.
Biolith tiles by Biomason are made using technology that harnesses power found in nature. The manufacturer combines carbon and calcium to produce a final material made by microorganisms. The tiles are composed of 85 percent natural aggregate and 15 percent biologically grown limestone. The company says that for each 1 kilogram of bio-cement that is used in lieu of Portland cement, 1 kilogram of CO? is saved. Right now, they¡¯re only available as precast panels. In the future, perhaps they will be available in a pourable solution so that we can really start to think about a new option to our current concrete materials.
Hotel Zachary in Chicago, Illinois, sits next to historic Wrigley Field.
Limestone alternatives to concrete (Marelle Davey)
Status: Coming soon
Concrete is the elephant in the room when it comes to embodied carbon. It¡¯s why I¡¯m passionate about innovative and creative low-carbon concrete technologies. I was especially excited when I came across innovative solutions being hatched in my home state of Colorado.
One idea, developed at the University of Colorado, is to grow limestone in a lab via a carbon-sequestering process using algae. Once the limestone is grown, it still must be heated to create cement. But the carbon sequestered by the algae in the process offsets the emissions from its manufacture, resulting in net carbon neutral or even carbon-negative cement.
Another solution is to replace the limestone with a substance that does not emit as much carbon when transformed into cement. Startups (like Terra CO2 in Colorado) suggest limestone substitutes such as calcium silicate. These change cement production and deliver the same quality material while reducing the embodied carbon.