Data and Methodology
The CARE Tool uses the Zero Tool to estimate building EUIs. For more details on Zero Tool assumptions and methodologies, visit the Zero Tool About page.
Once an EUI has been estimated using the Zero Tool, the CARE Tool calculates operational emissions using the following data sources:
EPA Fuel Split
EPA fuel split assumptions by use type and geographic region are used to estimate how much of the building’s energy consumption is from gas and how much is from electricity.
Total Gas Emissions
Total gas emissions are determined using a standard gas emissions factor of 0.277 kg CO2e/kWh which assumes an industry standard 2.8% fugitive emissions leakage rate.
Total Electricity Emissions
Total electricity emissions are determined using:
- If Default Electricity Grid Emissions is selected: EPA eGRID electricity emissions factors. With this selection CARE assumes the same electricity emissions factor every year. The version of eGRID currently in the CARE Tool is eGRID2020.
- If a Grid Emissions Scenario is selected: NREL’s Cambium long-run marginal emissions factor projections. With this selection, CARE is able to assume a different electricity emissions factor every year based on NREL’s projected electricity grid changes. The version of Cambium currently in the CARE Tool is 2021 Cambium.
- If Enter Your Own Grid Decarbonization Year is selected: The CARE Tool assumes a linear reduction from the project’s current eGRID emissions factor to an emissions factor of zero by the year entered.
If the option to Install all electric systems and equipment is selected, all emissions are assumed to come from electricity. If a Percentage of electricity produced by on-/off-site renewables is chosen, that percentage of electricity emissions are multiplied by an emissions factor of zero.
Embodied Emissions
The calculator uses embodied carbon benchmarks to calculate cradle-to-gate embodied emissions intensities for new buildings and renovated buildings. For renovated buildings, the tool covers structure, envelope, interiors, mechanical, electrical, and plumbing (MEP) systems. The tool does not include furniture, site and landscaping, or demolition/end-of-life. Units are kgCO2e/sf of building floor area. Each reuse option is assigned an embodied emissions intensity. In the calculator, the Total Embodied Emissions Intensity for a New Building or an Addition is based on the Type of Structure selected, with modifiers available to account for low-carbon materials or high-performance systems. The tool does not use building use as an impacting factor for Emissions Intensity due to lack of data points in existing benchmarking data.
The Total Embodied Emissions Intensity for a Building Reuse scenario is the weighted sum by floor area from Structural, Envelope, Interior, and Mechanical, Electrical, and Plumbing (MEP) plus an Addition if applicable.
Data in the CARE Tool is aligned where possible with the EPIC (Early Phase Integrated Carbon Assessment) Tool, which evaluates emission scenarios for new buildings. A “New Building” scenario in the CARE tool produces similar results to “Best Practice” scenarios in EPIC, when all building characteristics match.
New Buildings and Additions
The CARE tool considers Additions to be equivalent to New Buildings in Emissions Intensities per floor area. Emission Intensity benchmarks for new buildings were arrived at by analyzing embodied carbon data gathered from multiple sources.
All the studies used in the analysis, except for the Mechanical, Electrical, and Plumbing and Tenant Improvements studies by the Carbon Leadership Forum, included structure, foundations and envelope. Adjustments to the studies were made so that their values all accounted for structure, foundations, envelope, building interiors, and MEP systems.
To represent a range of typical new building construction, three categories of building types were established based on embodied carbon intensity. Because structural systems and materials have the largest impact on embodied carbon, the three building types are defined by type of structure rather than by use.
The benchmarking data analysis resulted in the following emissions intensities ranges and averages for the three building types:
- Wood — Small wood frame buildings; 200 – 450 kg/m2. Average 250kg/m2
- Hybrid Wood + Steel/Concrete — Mixed wood + concrete or steel structures: 270 – 500kg/m2. Average 325kg/m2
- Steel and/or Concrete — Mid-rise to high-rise, concrete / steel structure: 360 – 625kg/m2. Average 500kg/m2
| Type of Structure | Whole Building Emissions Intensity (Kg CO2e/sf of floor area) | Source | Notes |
|---|---|---|---|
| Wood | 23.23 | Aggregated analysis of multiple whole building life cycle assessment benchmarking studies:Carbon Leadership Forum Embodied Carbon Benchmark Study, sorted for whole-building LCA and by building sizeLife Cycle Assessment (LCA) for Low Carbon Construction: Mechanical, Electrical, and Plumbing in Commercial Office Buildings. Carbon Leadership ForumLife Cycle Assessment (LCA) for Low Carbon: Tenant Improvements in Commercial Office Buildings. Carbon Leadership ForumNAHB Single Family Home Embodied Carbon Study (Athena)Athena 2017 Embodied Carbon Benchmarking Report – Ten residential projectsRESIDENSITY : a carbon analysis of residential typologies by Adrian Smith + Gordon Gill (ICE)Embodied carbon data from Siegel & Strain Architects (ICE), Miller Hull (Tally) and Skanska, Goody Clancy (Tally) and others. | Adjustments to benchmarking data were made where components such as Interiors or MEP were missing to maintain consistency across all studies. |
| Hybrid | 30.19 | ||
| Steel/Concrete | 46.45 |
Structural System
The Embodied Emissions Intensity of the Structural System is based on the Type of Structure selected; Wood, Hybrid Wood + Steel/Concrete, or Steel and/or Concrete. The Emissions Intensity assigned to each Type of Structure represents a percentage of the whole building emissions of a New Building. This percentage was derived from the same benchmarking analysis of whole new buildings.
| Structure Type | % of Whole Building Emissions |
|---|---|
| Wood | 50% |
| Hybrid | 60% |
| Steel/Concrete | 70% |
For each structural type, these percentages are multiplied by the whole building emissions intensity to establish the emissions intensity of structure alone, resulting in the Structural System Emissions Intensities tabled below.
| Structure Type | Structural System Emissions Intensity (kg CO2e/sf of floor area) |
|---|---|
| Wood | 11.61 |
| Hybrid | 18.12 |
| Steel/Concrete | 34.84 |
To calculate Structural System Reuse, this Structural system EI is multiplied by the selected percentage of Extent of Structural Reinforcement or Replacement to calculate the total Embodied Emissions Intensity of the Structure.
If the option for an independent Lateral Upgrade is selected, a factor of 12% of a new structure‘s intensity is added to the structure’s Embodied Emissions total. This 12% is derived from SEAOC study indicating global warming potential impacts per structural component type: gravity system, foundation system, and seismic system.
![\[Structural Total = (User Input\% * EC intensity Of Structure) + (EC intensity Of Structure * Lateral Upgrade Factor)\]](https://www.caretool.org/wp-content/ql-cache/quicklatex.com-a73f7e681ec71face08ba9aaeb8b2138_l3.svg "Rendered by QuickLaTeX.com")
Structural Modifiers
If the Responsibly Sourced Timber modifier is selected, the Structural Total is reduced by 3% for Wood and Hybrid type buildings.
If the Low Embodied Emissions Concrete modifier is selected, the Structural Total is reduced by 9-17%, depending on the building’s Type of Structure.
To arrive at these values, the following studies were used to determine the percentage of wood and concrete in each type of structure:
- Japan Sustainable Building Consortium, 2014. CASBEE for New Construction Technical Manual 2014 Edition. Institute for Building Environment and Energy Conservation (IBEC): Tokyo, Japan.
- Milaj, K., 2016. Assessment of Environmental Impacts of Wood Substitution in Commercial Construction. Oregon State University.
- SOM, 2014. Timber tower research projects. Skidmore, Owings & Merril LLP.
A reduction factor is applied to the percentage of the Emissions Intensity represented by the relevant material. For low emissions concrete, a reduction of 24% is applied and for timber a reduction of 21% is applied. These reductions align with switching from EPIC’s Best Practice to Low Carbon options and are based on these studies:
- Carlisle, S., Waldman, B., Lewis, M., and Simonen, K., 2021. 2021 Carbon Leadership Forum Material Baseline Report. Carbon Leadership Forum, University of Washington. Seattle, WA.
- NRMCA, 2019. Appendix D: NRMCA Member National and Regional LCA Benchmark (Industry Average) Report. National Ready Mix Concrete Association.
Envelope Reuse
The Envelope Reuse category takes input entered under Existing Building Characteristics with assumptions of building geometry to establish the square footage of glazed (windowed) and unglazed (opaque) exterior wall area and the roof area of the model. The tool assumes the building footprint is a square with a floor-to-floor height of 13’-0”.
![\[Unglazed Wall Area = (\sqrt{Roof Area} * 4 * Floor To Floor Height * Reused Floor Above Grade) * (1 - Window To Wall Ratio)\]](https://www.caretool.org/wp-content/ql-cache/quicklatex.com-bc57bb24638354b5516ebe20a59ccfbe_l3.svg "Rendered by QuickLaTeX.com")
![\[Glazed Wall Area = (\sqrt{Roof Area} * 4 * Floor To Floor Height * Reused Floor Above Grade) * Window To Wall Ratio\]](https://www.caretool.org/wp-content/ql-cache/quicklatex.com-c3bd017ea518c1adf367801ba2b9ef95_l3.svg "Rendered by QuickLaTeX.com")
![\[Roof Area = \frac{Total Floor Area Reused}{Reused Floors Above Grade + Reused Floors Below Grade}\]](https://www.caretool.org/wp-content/ql-cache/quicklatex.com-91fad6f8429a580838cb5c6a5005a009_l3.svg "Rendered by QuickLaTeX.com")
For each option selected in Exterior Walls, Windows, and Roofing, the respective Emissions Intensity is multiplied by the component’s square footage. These total emissions are then summed and normalized by the total building floor area reused to arrive at the Envelope Reuse kgCO2e/sf of building floor area.
![\[Envelop Total = \frac{(EC intensity of Exterior Wall * Unglazed Wall Area) + (Ec intensity of Glazing * Glazed Wall Area) + (EC intensity of Roofing * Roof Area)}{Total Floor Area}\]](https://www.caretool.org/wp-content/ql-cache/quicklatex.com-7f3d817d610783957c5dfa1a72255a57_l3.svg "Rendered by QuickLaTeX.com")
If the Low Embodied Emissions Envelope modifier is selected, the Envelope Total is reduced by 66%. This reduction aligns with EPIC’s “Low-Carbon” Cladding scenario.
Exterior Walls
| Exterior Walls Option | Emissions Intensity (kg CO2e/sf of opaque wall) | Source | Notes |
|---|---|---|---|
| Clean/Seal/Coat | 0.35 | American Coatings Association | |
| 50% Masonry Repair/Repointing | 0.6 | Bras, A., Faria, P., (2017). Effectiveness of mortars composition on the embodied carbon long-term impact. Energy and Buildings, Volume 154, 1 November 2017, Pages 523-528. | |
| Masonry Repair/Repointing | 1.2 | ||
| Replace 50% Exterior Wall Assembly, Includes Insulatio | 4.38 | Tally | Exterior wall assembly assumed is brick cladding including steel shelf angles and Type N mortar, 4” mineral wool insulation, AVB membrane, fiberglass mat gypsum sheathing, 6” metal stud framing and painted gypsum wall board. This aligns with EPIC Best Practice for Envelope. |
| Replace Exterior Wall Assembly, Includes Insulation | 8.75 | Tally |
Windows/Glazing
Tally was used to source emission intensities for the Minor and Medium window repair options. The Major option aligns with EPIC’s Best Practice for Glazing.
| Windows/ Glazing Option | Emissions Intensity (kg CO2e/sf of glazing | Source | Notes |
|---|---|---|---|
| Minor: Weather Strip/Restore Frame | 0.31 | Tally, “Life Cycle Assessment of Residential Windows: Saving Energy with Window Restoration” | This study conducts LCA for window restoration. |
| Medium: Reglaze Existing Frames | 3.38 | Tally | The assumption for new glazing is a 1” Insulated Glazing Unit with ¼” glazing, argon gas, and a low-E coating. |
| Major: Replace Windows | 13.65 | Tally | This aligns with EPIC Best Practice for Envelope. |
Roofing
Tally was used to source emission intensities for roofing, assuming an assembly of an HDPE sheet vapor barrier, exterior-grade plywood sheathing, 5” of polyisocyanurate rigid foam insulation, and EPDM roofing membrane cladding.
| Roofing Options | Emissions Intensity (kg CO2e/sf of roof area) | Source | Notes |
|---|---|---|---|
| Minor: Restore/Repair | 0.24 | Tally | Assumes only cladding on 25% of the roof area is replaced |
| Major: Replace All Roofing, Includes Insulation | 2.37 | Tally | Assumes the entire assembly on 100% of the roof area is replaced. |
The option to Insulate Walls adds to the Exterior Wall emissions intensity. It assumes an assembly of 4” of mineral wool, an HDPE vapor barrier, and a 3 5/8” metal stud wall with one layer painted gypsum wall board at an emissions intensity of .89 kg CO2e/sf of opaque wall, per Tally.
The Low Embodied Emissions Envelope modifier assumes switching from brick cladding to a wood rainscreen of matching R-value performance. This results in a 66% reduction in the exterior wall emissions intensity.
Interior Reuse
For each Interior Reuse option, the extent entered as percentage of floor area, is multiplied by the corresponding emissions intensity. All three results are summed.
![\[Interior Total = (EC intensity Of Restore * \% Extent of Restore) + (EC intensity Of Ne Finishes * \% Extent of New Finishes) + (EC intensity of Rebuild * \% Extent of Rebuild)\]](https://www.caretool.org/wp-content/ql-cache/quicklatex.com-e4df0ab3bf802af1066657adde697457_l3.svg "Rendered by QuickLaTeX.com")
| Interior Reuse Option | Emissions Intensity (kg CO2e/sf of floor area) | Source | Notes |
|---|---|---|---|
| Restore/ Refurbish Existing Finishes | 0.13 | Swedish Environmental Research Institute | This option assumes refinishing of wood flooring. |
| New Finishes | 2.1 | Life Cycle Assessment (LCA) for Low Carbon: Tenant Improvements in Commercial Office | This option assumes rooms are not being reconfigured and thus no new walls. It accounts for only new flooring, paint, and ceilings. |
| Rebuilding/ Reconfiguration | 4.8 | Buildings. Carbon Leadership Forum | This option assumes new flooring, paint, ceilings, partitions, interior glazing, and doors. It aligns with EPIC’s “Best Practice” option for Interior Fitout Specification. |
Mechanical, Electrical, Plumbing Systems Reuse
The CLF MEP LCA report is the basis of emissions intensities for MEP. The report establishes emissions intensities for systems based on building size: S, M, L, XL. The Major: Replace All Systems option uses these intensities, and also aligns with EPIC.
The New Equipment, Reuse Distribution option removes distribution components: ducts, sheet metal, insulation, piping, conduits, from the intensity of the full replacement option. Because the CLF MEP LCA report does not include plumbing fixtures in its totals, this option does not account for new plumbing fixtures.
The Minor: Repair/Refurbish considers only distribution and assumes 10% is replaced.
If the High Performance Mechanical, Electrical, Plumbing Systems modifier is selected, emissions intensity values are modified as shown in the table.
| Mechanical, Electrical, Plumbing Systems Reuse Option | Building Square Footage threshold | Emissions Intensity (kg CO2e/sf of floor area | High Performance System: Emissions Intensity (kg CO2e/sf of floor area) | Source | Notes |
|---|---|---|---|---|---|
| Medium: Replace Equipment, Reuse Distribution | N/A | 0.25 | 0.25 | Rodriguez, B.X., Lee H.W., Simonen, K., Huang, M., (2018). Life Cycle Assessment (LCA) for Low Carbon Construction: Mechanical, Electrical, and Plumbing in Commercial Office Buildings. Carbon Leadership Forum, University of Washington. Seattle, WA. | This option assumes replacement of 10% of distribution replaced |
| Medium: Replace Equipment, Reuse Distribution | if building area ≤ | – | – | new equipment only, remove ducts, sheet metal, insulation,piping, etc. Does not include plumbing work because CLF report only measures plumbing dist, no fixtures. | |
| S | 25,000 | 1.3 | 1.3 | ||
| M | 80,000 | 2.1 | 2.1 | ||
| L | 300,000 | 3.1 | 2.7 | ||
| XL | 800,000 | 2.3 | 3.2 | ||
| Major: Replace All Systems | if building area ≤ | – | – | ||
| S | 25,000 | 4.1 | 6.2 | ||
| M | 80,000 | 4.6 | 5.8 | ||
| L | 300,000 | 5.9 | 6 | ||
| XL | 800,000 | 4.8 | 6.8 |
For an Addition and New Building scenario, the High Performance Mechanical, Electrical, Plumbing Systems modifier incorporates a 4% increase to the Total Embodied Emissions Intensity. This was arrived at through the same CLF LCA MEP source study which indicates that high-performance systems add approximately 30% to a systems emissions intensity, and that the systems represent 12% of a whole building intensity.
Source: Data and Methodology