I couldn’t find my original post, so hopefully not a big deal that I am recreating.
I am working on a sustainability master plan and setting a carbon budget (before offsets) for a 25 acre mixed-use community/neighborhood. This is in the United States and will be predominately residential (townhomes & multifamily dwelling units).
We like to take a good/better/best approach when conceptually planning, so this is where I landed was:
Good = 14 kgCO2e/m2/yr (700 kgCO2e/m2 across 60 years)
Better = 10 kgCO2e/m2/yr (600 kgCO2e/m2 across 60 years)
Best = 8 kgCO2e/m2/yr (480 kgCO2e/m2 across 60 years)
I realize the per year metric is likely confusing for embodied carbon, but I was following the framework that Denmark set out for their budget, which has a yearly requirement across a 60 year life cycle. Also, this benchmark/budget should not include operational carbon and is before renewable/offsets are applied.
How I came to these conclusions:
Good = best practice, material design optimization, reduce amount of materials in the project. (60 year life cycle)
Better = IFLI benchmark (500 kgCO2e across 50 years)
Best = Denmark’s carbon budget policy in effect on 2023. (60 year life cycle)
I wish there was more data to reference… Looking at CLF’s benchmarking study from 2017 (https://carbonleadershipforum.org/embodied-carbon-benchmark-study-1/), it is very lackluster and isn’t close to including all systems. The spread for low-rise resi is about 100-400 kgCO2e/m2, which obviously comes in below the IFLI requirement…so it’s missing stuff.
The KPIs/targets I’ve listed above would be for solely embodied carbon. It would include all major systems/components of the building (foundation, structure, enclosure, interiors, equipment). I used the IFLI Zero Carbon language to guide/determine this.
Landscape hasn’t been considered (yet) and civil infrastructure is being discussed (but not quantified yet either).
Energy/Water use (B6 & B7) are being tracked, but in a different bucket.
We pull it all together in a holistic stacked bar graph for the entire neighborhood.
I haven’t been able to fully determine what scope is included in Denmark’s policy. The carbon budget starts at 12 kgCO2e/m2/yr (in 2023) and ratchets down to 5 kgCO2e/m2/yr (in 2029). The lifecycle is a 50 year one. I unfortunately can’t read the graphics (language), so I don’t know what building aspects are required. A One-Click LCA article (Bæredygtighedsklassen: a new measure to decarbonise construction in Denmark - One Click LCA® software) is saying 50 year life cycle period for A1-A5, B4, B6, C3, C4, and D.
I’m working on low-rise residential benchmarking in Canada, and have completed a study of 190 models for the federal government, 34 as-built homes in Nelson, BC and 503 as-built homes in the Toronto region. We have been counting A1-A3 emissions for the structural, enclosure and main finishes (flooring, wallboard, ceiling) for the homes.
Depending on material selection, we’ve seen the as-built homes range from an average of 150 kg CO2e/m2 (of heated floor area) to 190. We’ve seen results as high as 560 and as low as 72. But with about 550 as-built examples it seems that the 150-190 range is a reasonable benchmark range.
Not sure how you’d want to turn that into emissions across 60 years, as we’re not counting any material replacements (we’re looking out between now and 2050 in these studies, and none of the materials we’re including should require replacement in that timeframe).
We’ve been recommending a metric of “carbon use intensity” that includes material emissions and operational emissions added together over a chosen number of years… usually to align with a climate target such as 50% reduction by 2030. In this way, we can steer designers and regulators to a single metric that ensures their targets are being met while not dictating how the home gets to that target, since depending on location it may be best to focus on energy source, energy efficiency or material selections, or some ideal blend of all three.
The reports are too large to attach here, but you can find them at Builders for Climate Action: https://www.buildersforclimateaction.org/
Thank you so much for responding and including this data.
Even if we aren’t apples-to-apples on scope, seeing your study results average approx. 150-190 kgCO2e/m2 for low-rise residential (for structural, enclosure, and main finishes across A1-A3) is a fantastic reference point.
I resonate your position on “Carbon Use Intensity”. This is something we have used as well to pull it all together when discussing total carbon emissions with our clients. We have been using a graphic like this to show the relationships between embodied, operational, and renewable generation:
I don’t know if it helps your prelim calculations but our 3rd party Verified 2018 LCA on our wood planks for interior walls floor and ceilings came back solid… negative carbon A1-A3 we are at -8.09E+00 / GWP 100 (kg CO2 eq).
I can get you the docs if you need or find them @mafi.com
Sounds like you have some good help on this forum.
If I may inspire an additional matter for your consideration:
Where some of this development may not be starting for several years, do you have a way to ratchet your targets down? You wouldn’t want building work starting in 2, 5, or 10 years to be measured against the benchmarks that are labelled “Good, Better, Best” based on 2022 practice.
@mike.kovacs - you bring up a valid concern. This is definitely something that needs to be considered. Having good/better/best targets for different phases of the development is an excellent idea.
