Whole Life Carbon Assessment

C.Scale generates time series estimates of a building's carbon emissions and organizes those emissions by emission category and life cycle stage.

A1-3: Upstream Product Emissions

A1-A3 emissions are calculated from a bill of materials (e.g., life cycle inventory) inferred from the user's description of a building. The exact method for generating that bill of materials and calculating A1-A3 emissions varies by building assembly.

For each contributor $i$, embodied emissions in life cycle stages A1-A3 are assessed with the following expression:

$${Assessed\ emissions}_i=\ A\ast x_i\ast c_i$$

Where A is the total building area, $x_i$ is the quantity of the contributor $i$ per building area, and $c_i$ is the carbon intensity per unit of the contributor $i$.

For example, a 10,000 square foot 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 (values 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:

$$10,000\ sf\ast4\ \frac{lbs\ rebar}{sf}\ast0.5\ \frac{kg\ CO_2e}{lb\ rebar}=20,000\ kg\ CO_2e$$

Other pages in this section detail the calculation of A1-A3 emissions from structure, envelope, and other building assemblies.

A4-5: Construction Emissions

A4: Transportation of Materials to Site

All materials accounted for in A1-A3 must be transported to the site. C.Scale defaults to emission factors from the ASHRAE 240P draft guidance in table 6.5.2.1. These are conservative estimates of emissions per quantity of material. These data include a 0.5 return trip factor.

A5.1: Pre-Construction Demolition

Pre-construction demolition emissions are calculated per floor area of the demolished building, using a default factor of 35 kgCO2e/m2. This is a data-scarce category. Where project-specific data is available, this default can be overridden by the user.

A5.2: Jobsite Activities

Emissions from construction activities and land use change are included in A5.2.

Construction Activities

Construction activities include the use of tools, fuel, equipment, and energy on the building site. This includes site preparation, installation of materials, and other jobsite activities. As a default value, C.Scale assumes the carbon intensity of construction activities to be 40 kg CO2e/m2 of project floor area. Where project-specific data is available, this default can be overridden by the user.

Emissions from construction activities are proportioned out to indivudal building elements on a mass basis. For example, if a building's envelope accounts for 25% of its total building mass, C.Scale assumes the A5.2 construction activities associated with the envelope are 10 kg CO2e/m2, 25% of the default value of 40 kg CO2e/m2.

Emissions from Greenfield Development

Land use change emissions from greenfield development are counted in A5.2. For details on land use change emissions, see Site and Landscape.

A5.3: Jobsite Waste

For each material and building assembly, C.Scale assumes a percentage of the installed total is wasted during construction. For all waste incurred during A5.3, we calculate A1-A4 and C2-C4 emissions for the wasted material and assign it to A5.3 emission for that material's category. C.Scale's default (conservative!) waste rates are included in the table below.

Building Material/Assembly	Waste Rate
Concrete (all types)	5%
Reinforcing Steel	3%
Hot-Rolled Steel	10%
Cold-Formed Steel	10%
Dimensional Lumber	10%
Ply and OSB Products	15%
Engineered Timber	10%
CMU Block	5%
CMU Mortar	15%

B Phase: Use Stage

The use stage includes all emissions from the operation of the building from the completion of construction until the end of the reference service period.

B1: In-Use Emissions

Fugitive emissions from annual refrigerant leakage, as well as refrigerant leakage for equipment replaced during the operating life of the building, are counted in life cycle stage B1. This is treated in detail in the documentation section on Refrigerant Emissions.

Annual carbon storage in the landscape is also included in this phase.

B2-B5: Replacement and Refurbishment

C.Scale uses a simplified model of replacement and refurbishment. For all materials in the C.Scale model, the emissions associated with this replacement and refurbishment—including manufacturing, transportation, and installation of the new materials, as well as end-of-life emissions for any removed materials—are assigned to the year(s) determined by the user-selected refurbishment period.

B6: Operational Energy use

Life cycle stage B6 includes operational emissions from energy use. This is treated in detail in the documentation section on Operational Carbon.

C Phase: End of Life

Data from life cycle stages C1-C4 cover the process from building demolition to the final disposition of materials as input to recycling, waste recovery processes, or landfills.

C1: Demolition

C.Scale assumes that business-as-usual demolition practices will be 30% of the emissions used to construct the same asset. This value can be overridden with a project-specific value. C1 also includes emissions from refrigerant leakage of all removed equipment.

C2: Transportation to End of Life Processing

By default, C.Scale assumes that all waste travels 50 miles (80 km) to the nearest waste processing facility by truck with a 50% load. This distance can be overridden by user inputs.

C3: Waste Processing for Recycling, Reuse, and Recovery

Data for life cycle stages C3 are collected from regionally-appropriate industry-average EPDs.

C4: Landfill Disposal Emissions

Data for life cycle stages C3 are collected from regionally-appropriate industry-average EPDs. Where data is unavailable in the US, EPA Warm is used as a reference data source.

D Phase: Benefits Beyond the System Boundary

The D phase of a whole life carbon assessment includes environmental benefits and burdens beyond the system boundary. D phase emissions are typically reported separately from life cycle impacts and should not be combined into a total emissions value for reporting purposes.

D1: Potential Benefits from Recycling, Recovery, and Reuse

Data for life cycle stage D1 are collected from regionally-appropriate industry-average EPDs. Where this data was not available, we assume D1 to be zero.

D2: Benefits from Exported Energy

If a building generates more energy than it uses in a given year and exports that energy to the grid, the benefit of this export can be declared in module D2 which counts the avoided impact of grid electricity generation. For more information, see Avoided Emissions.