The 10 design commandments for cutting your building’s embodied carbonHow to reduce embodied carbon in the built environment
How to cut the embodied carbon of your building
“When I first came here, this was all swamp. Everyone said I was daft to build a castle on a swamp, but I built it all the same, just to show them. It sank into the swamp. So, I built a second one. And that one sank into the swamp. So, I built a third. That burned down, fell over, and then sank into the swamp. But the fourth one stayed up. And that’s what you’re going to get, son, the strongest castle in all of England.”
King of Swamp Castle, Monthy Python’s Holy Grail
Don’t build on a swamp!
This guide will show architects and other building designers how to effectively reduce the embodied carbon of a construction project. Avoid building castles on a swamp and follow these design commandments to achieve substantial and cost-effective emissions reductions, and learn how to achieve low carbon design in your projects.
To demonstrate the impacts, we have quantified the impacts of the commandments on a 7000 m2 (75,350 ft2) office building with 7 above ground floors of each 1000 m2 (10,760 ft2
When you begin working on embodied carbon, make sure that your building has a decent energy performance and such low carbon energy supply options as your locality can offer, and avoid sites where transport relies on private cars or with long transport distances for users. These provide a solid basis for further decarbonization.
10 design commandments that can help you cut embodied carbon
First, do no harm is the right approach also for embodied carbon. Adopting these practices in the design process enables projects to achieve embodied carbon reductions in the order of one third, with potential for cost savings in materials, also when retaining traditional structural material.
Optimizing the life-cycle impacts for a 60-year span is not worthwhile, if the need for the building is not sustainable, for example, due to ongoing demographic change or zoning changes elsewhere. This may be addressed by designing either a building that’s highly adaptable or with a modular transportable building that satisfies the demand for a shorter period of time.
Example building: if the service life is limited to 25 years, the annualized materials-driven carbon impacts are 120 % higher. In case the building can be converted to another use harm would be of lower order.
The soil conditions greatly impact the stabilization and foundations you will require. If your site requires massive foundations to support the building, reconsider the site. If you are committed to the site, see if you can place the building mass on the site to optimize the distance to bedrock as it likely varies within the site, and also consider opting for a less heavy structural solution, for example, timber or steel. Finally, avoid cast-in-place concrete, which tends to result to the heaviest of all structural solutions.
Example building: foundations share of embodied carbon impacts is 40 % when considering also replacements during life-cycle (not needed for foundations).
One Click LCA offers ready to use foundation scenarios for various soil conditions with five-meter depth intervals using different foundation technologies as well as soil stabilization and soil movement prevention.
It has often been said, but it bears repeating. Choosing wood structures, when the requirements allow for it, can reduce embodied impacts substantially in most projects. In our case building, this embodied carbon reduction – when measured over the whole life-cycle – would be in the order of 30% reduction.
Example building: the share of embodied carbon impacts for structural materials is always substantial, and in our case building, nearly three quarters.
One Click LCA’s Carbon Designer tool allows quick evaluation of impact of choice between common structural materials using building geometry.
Setting carbon performance requirements or other measures driving carbon reductions such as the use of recycled binders for concrete, for example, allows reducing emissions in a meaningful and effective way for achieving exactly the same design and performance. This strategy works effectively for all materials where supply is competitive and some suppliers are willing to supply products with improved environmental performance.
Example building: in the example building, when structural concretes and steels were changed to lower impact products, the whole building materials life-cycle impacts were reduced by 10%. Looking carefully at what you source can allow going substantially lower still.
One Click LCA’s materials database contains over 10 000 different construction materials environmental impact profiles for different products, technologies, suppliers and products. There’s also a module to create your own product mixes e.g. for specific concrete recipes; and you can send us any new EPDs that you plan to use if you do not find them.
Example from One Click LCA US database: concrete embodied carbon impacts range from below 200 to over 500 kg CO2e / m3
As a general rule, a simple shape is more materials- and energy-efficient. Building in a square shape is not always possible due to daylighting, zoning, functional or space distribution requirements. A more complex building shape drives external walls demands, and also requires additional access corridors. In case the building requires additional staircase and elevator shafts in different locations, this also creates demand without additional corresponding available room area.
Example building: if the building would be built as a three-story elongated building, the embodied carbon impacts are approximately 10% higher. Also, this increases the envelope area, and, as a result, the energy loss via building envelope.
One Click LCA’s Carbon Designer module allows considering impacts of number of floors, shape, floor height and additional parameters for the materials demand as well as resulting embodied carbon impacts.
Slabs are a major contributor to building embodied carbon. As opposed to the envelope area, the amount of slabs scales linearly with the internal area required. Slabs provide structural, acoustic and fire resistance capabilities for the building, among others, and may embed piping or other installations. Reducing the net thickness of slabs with 10 cm reduces the building envelope height correspondingly, thus saving materials from slabs and walls, and energy via reduced conductive loss. Some good practices include using innovative technologies, including Deltabeam, Bubbledeck, and hollow core slabs in concrete construction. This kind of change can reduce building life-cycle embodied impacts by approximately 6%.
Example building: the share of embodied carbon impacts for all slabs is around 45%.
One Click LCA’s database includes 50+ pre-built slabs as well as ready to use solutions for most innovative beam and deck technologies. A module for creating and calculating own constructions is also available.
Souce: Eyad Sayhood, Mohammed Mahmood. “Non-Linear Behavior of Composite Slim Floor Beams with Partial Interaction”, European Journal of Scientific Research, 56(3):311-325, July 2011.
It is also worth noting that having shorter grid spans for columns allows for making lighter and less steel- and cement-intensive slabs. This will have to be balanced against the impact it has on materials used in the columns and potential impact on the future adaptability of the spaces. Some types of slab systems also have higher impacts, and care should be paid on the overall design and choice of the floor slabs used.
If your zoning laws allow it, do try to reduce the number of parking spots, in particular, underground parking spots and places in parking towers. If you have to have parking spaces below the building, consider raising the building so that the building stands on pillars with an open area for parking below the building. This will save a substantial amount of materials in needless walls around the parking spaces.
Example building: the share of embodied carbon impacts for parking structures is 7% (in the initial case with the parking mix heavily dependent on private cars). If the initial mix of underground and above ground parking could be shifted to only above ground parking places, these impacts would be approximately 69% lower.
One Click LCA’s Carbon Designer module includes optional calculation for underground parking floors. Further, operational transport carbon impacts can be accounted for using One Click LCA’s Site selection impacts tool, which is also part of NS 3720 tool.
As floorplan configurations may often change, it is a good practice to use reusable and possibly movable internal walls to the extent that they work for the building function. Same goes for electrification that tracks seating arrangements in office buildings. If this practice is not applicable to your project, consider applying construction methods that allow removing the boards intact.
Example building: if in our example buildings we assume that one-half of the internal walls are load-bearing, and the balance would require rebuilding every decade, the material life-cycle impacts would be circa 4% higher, compared to the case where wall configuration can remain until the material reaches the end of its service life.
One Click LCA allows you to set the service life for each material to reflect their actually foreseen replacement frequency as well as eventual reuse.
Movable office walls
If your cladding/façade material is providing mainly an aesthetic function, consider omitting the layer. If your internal ceilings are not providing e.g. acoustic or fire protection, the entire element might be removed. This will also allow better maintenance access to installations and cabling. Same considerations apply also to floorings, a polished concrete flooring can be a good option for some types of spaces (while not all).
Example building: the share of embodied carbon impacts for internal ceilings is circa 1%. Furthermore, the building is cladded with an aesthetic steel facing, whose life cycle impacts are circa 2%. Avoiding the flooring altogether would achieve impact reductions of the order of 4%.
Polished concrete flooring
Investing in durable materials means fewer replacements over time, which means fewer carbon emissions, less waste generated, lower life-cycle cost and less tenant disruption. What is a durable and suitable material for your market varies depending on the conditions –however, the principle remains the same.
Example building: depending on your project conditions, specifying longer-lived systems can save both carbon and money. This will be however very dependent on conditions but can achieve several percentage points of life-cycle embodied carbon reductions – in our example project between extreme cases the difference would be in the order of 3%.
There’s a lot more – including many innovative designs and products you can apply, and practices such as ensuring structural material strengths are not generalized but optimized for different uses, buying with takeback agreements, and so forth. You can also check out Larry Strain’s article or a recent piece by BRE’s Daniel Doran for further thoughts.
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