At Carbon Title, we have a commitment to a scientifically rigorous calculation of carbon emissions that stands up to scrutiny. Consequently, we have collaborated with a third party carbon calculation model, c.scale, developed by climate scientists and a world-renowned architectural firm, EHDD.
The scope and methodology used in reaching our calculations is below. As we update and further refine the model, we will continue to update these materials. Please direct any questions to info@carbontitle.com.
Time Horizon: The c.scale model uses a 30-year time horizon.
Life Cycle Stages: The c.scale model integrates data from life cycle modules A1-A3 and B2-B6. These correspond to the impacts of the materials used in the project, their replacement over time, and the project’s operational energy use. When biogenic carbon is counted, some end-of-life impacts (from modules C3-C4) are assessed during the product phase.
Embodied Carbon Scope
The c.scale model considers embodied carbon from a number of sources. Its scope may be distinct from other tools.
Operational Carbon Scope
The c.scale model considers the emissions associated with a project based on averages by state. Onsite fossil fuel use is assumed to be natural gas, and its proportion of total energy use is based on averages from the CBECS and RECS databases.
Sequestered Carbon Scope
The c.scale model includes sequestered carbon from timber structural systems, site landscaping, and planted roofs. Carbon sequestration by site landscaping is calculated annually. Planted roof and structural sequestration are calculated over the 30-year time horizon then annualized. Our approach to sequestration is detailed in the appendix on biogenic carbon.
Embodied Carbon Emissions
For each contributor i, embodied emissions assessed by the c.scale model are evaluated with the following expression:
Where A is the total building area, xi is the quantity of the contributor i per building area, and ci is the carbon intensity per unit of the contributor i .
For example, a 10,000 sf building may use 4 pounds of reinforcing steel per square foot of floor area, and the reinforcing steel may have a carbon intensity of 500 grams (0.5 kilograms) of carbon dioxide-equivalent emissions per pound of steel (not actual values and for illustrative purposes only). Taking the product of these three hypothetical quantities yields the contribution of reinforcing steel to that building's embodied carbon emission:
In each part of its model, c.scale sums the assessed emission of many individual contributors. While simple summation is acceptable in some cases, some materials will be replaced before the target date. For these materials, the emissions are assigned to the year(s) in which they're replaced, and a multiplier is added to the total summation. The total embodied emissions assessed by Carbon Title/EPIC are represented by this expression:
For n number of contributors to the embodied emissions, where A is the total building area,xi is the quantity of the contributor i per building area, ci is the carbon intensity per unit of the contributor i , and ri is the number of replacements of the contributor i before the target date.
Operational Carbon EmissionsThe operational emissions of the project are assessed annually and summed across all years before the target date. The equation is similar to the equation for embodied emissions, with two key differences: first, the quantity x is substituted for the energy use intensity (EUI) e; second, the equation is a double summation, once across all the fuel types in the building and again across all years between the building's completion and the target year. The total operational emissions assessed by c.scale are represented by this expression:
For m total years between the building's completion and the target year and across o fuel types, where A is the total building area, etj is the energy use per building area (EUI) in year t of fuel j, and ctj is the carbon intensity per energy unit in year t of fuel j
Total Landscape EmissionsLandscape emissions assessed by the c.scale model are evaluated with the following expression:
For p number of contributors to the embodied emissions, where A is the total planted area of landscaping type k and ck is the carbon intensity of maintenance of landscape in year t per area of planting k.
Total Carbon EmissionsThe total carbon emissions assessed by the c.scale model can be represented by this expression:
With variables as defined in the preceding sections.
Biogenic Carbon SequestrationIn the c.scale model , landscaping and the use of structural timber contribute to biogenic carbon sequestration. Carbon sequestration in structural materials is assessed once at the beginning of the project, and landscape sequestration is assessed each year. Biogenic carbon sequestration is evaluated with the following expression:
Where xi is the amount of carbon-sequestering timber structural material i, Ci is the carbon sequestration per unit i, Ak is the area A of carbon-sequestering planting type k, and Ck is the carbon sequestration in year t per area of planting k.
For more information on how biogenic carbon sequestration is treated within the c.scale model, please contact info@carbontitle.com.
In development of the c.scale model, we have used the Carbon Leadership Forum's 2017 Embodied Carbon Benchmark Study as a reference point for the embodied carbon emission intensities across building types. While the Carbon Leadership Forum (CLF) study acknowledges that the study uses data from "non-aligned studies that used different building scopes, different LCA data, and different LCA methods" and "is not a statistically representative sample of current building practices," it remains one of the most comprehensive references for embodied carbon emissions from buildings.
To compare our model to the CLF study, we assessed 160 cases in our model. We assumed each building had four equal-area stories and modeled across five total floor areas (20,000 sf, 40,000 sf, 60,000 sf, 80,000 sf, and 100,000 sf) across four use types (assembly, education, multi-family residence, and office). For each building of each size and use type, we evaluated the carbon footprint for four structural systems (mass timber, reinforced concrete, steel frame, and light wood frame).
The emissions from these buildings were assessed both as a Base Case building in the c.scale model and as a "Low C " case. The Low C case includes carbon reduction measures for "low carbon" specification (for concrete, steel, envelope, and interior), 50-year envelope refurbishment, and 20-year interior refurbishment.
Distribution of embodied carbon intensities generated by the c.scale model (n=40 for each use type).
Distribution of embodied carbon intensities in the Embodied Carbon Benchmark Study (education, n=147; multi-family, n=61; office, n=279; public assembly, n=67).
