Methodologies

The Embodied Carbon Tool enables users to estimate manufacturing greenhouse gas emissions from forest products. The tool uses geographically relevant data from verified Life Cycle Assessments (LCAs) or Environmental Product Declarations (EPDs). The methods that underlie the embodied carbon tool are largely based on the quantification approaches published in the USDA Entity Guidelines Chapter 5: Methods for Managed Forest Systems (Murray et al. 2024) Section 5.2.2. LCA Quantification of HWP Emissions (Cradle to Gate, From Forest to Product Manufacturing Gate) and explained in CORRIM report (USE 2024).

A user has two choices for their analysis: (1) wood primary products or (2) harvested logs. The tool delivers the cradle-to-gate embodied carbon values separated into the A1 (raw material supply), A2 (transportation), and A3 (manufacturing) following the construction works life cycle stages as defined in ISO 2017.

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Figure 1: Generic Presentation of Life Cycle Stages of HWPs in LCA Studies (from Murray et al (2024)

Summary of Inputs

Product Level

Selected Product: This is a primary or secondary wood product made in the U.S. Users input a volume of material in units that correspond to the default unit provided in the drop down menu. Users can also select which region the product is derived from from one of four regions in the US: Coast, Rocky Mountain, South, North. If there is no embodied carbon data for a product in a specific region, users may also select National or North America as options.

Material Amounts: A user enters a quantity in the units that correspond to the selected product default unit, described in Table 1 below:

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Table 1: Wood Products and their associated default units

MBF = Thousand board feet

MSF = Thousand square feet

M³ = Cubic meters

MCF = Thousand cubic feet

Forest (Harvested Log):

Region: Users select from one of four regions in the US: Pacific Coast, Inland Northwest, South, North

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Figure 1: Map of regions, which are combinations of the 10 US Forest Service RPA regions.

Log Type: Users select a log type from the following drop down menu: Softwood Sawlog, Softwood Pulpwood, Hardwood Sawlog, Hardwood Pulpwood, Softwood, Hardwood.

Harvest Quantity: Users enter the volume of harvested log that leaves the site (i.e., is delivered to a mill) corresponding to the selected log type. Users can choose between the following common log units: board foot (BF), MBF, CF, CCF, m³, short ton, metric ton.

Summary of Outputs

Product

Embodied Carbon Results: For each product selected, the total cradle-to-gate embodied carbon (A1-A3) estimate, as well as for the individual stages (i.e., A1, A2, A3), are displayed for the quantity of material provided. These are displayed in Kg CO2e. These are also summarized by region and totaled.

Forest (Harvested Log):

Embodied Carbon Results: For each region and log type selected, the downstream embodied carbon results are displayed, representing the weighted average of the products that are made from the harvested log. These are summarized by region.

Note1: “Other industrial products” was taken as the average embodied carbon results from the softwood lumber, hardwood lumber, softwood plywood, hardwood plywood, particleboard, OSB, MDF, hardboard, and fiberboard in the region.

Note2: “Fuel and other” embodied carbon was calculated by running 1kg biomass through the CORRIM generic boiler model with the inputs specific to regional lumber production”.

Scope

The data used for calculating cradle to gate embodied carbon limited to US forests and products.

Carbon Pools

Biogenic Carbon Storage: The carbon stored in the log or product

Fossil carbon emissions: Fossil emissions estimated through cradle-to-gate life cycle assessments.

Temporal scale

The life cycle assessments or life cycle databases from which the GWP values are derived are cradle to gate, meaning they include A1, A2, and A3. Some of these emissions (e.g., A1) may have occurred in past years as they are associated with silviculture management. Manufacturing and transportation likely occurred over a 1-2 year period.

Caveats and Context for Users

The embodied carbon tool was developed to provide users with the comprehensive suite of published embodied carbon data on wood products in the US, derived from either third-party verified EPDs or LCAs. Data are aggregated regionally for four regions in the U.S., which is currently the most granular assessment of industry-wide embodied carbon information. In some cases there is no embodied carbon information available for a specific region/product because the product is either not made in that region or published life cycle assessments are not available to include in the database. In these cases,users may apply National or North American scale data.

The data are sourced from third party verified EPDs or published LCAs listed in Annex 3 and these sources are all available in the tool.

Sources of Uncertainty

EPDs are only considered valid for five years, and therefore the EPD data integrated into the tool were published post-2020. The tool DOES include expired EPDs if there are no other data available, and in those cases, that information is transparently presented to the user in the platform. .

In addition, the default log to product allocations and product to end-use allocations are adapted from Smith et al (2006). Efforts are underway to update both of these sets of parameters.

Forest/Harvested Log to Product Allocations

The data used to create the ratios of harvested log to primary product was adapted from Smith et al (2006) Table D6. They were reallocated from nine regions to four regions to match the regional delineations applied for the Embodied Carbon Tool. The methodology is explained in the CORRIM final report to the US Endowment (2024) and presented below::

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The non-structural panels in Smith et al (2006) Table D6 were further broken out into particleboard, MDF, hardboard, and fiberboard based on the annual production reported in CORRIM reports and then weighted averaged using total roundwood fractions for nonstructural products (see Table 7 from CORRIM report).

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Table 2: “Table 7” from CORRIM’s final report to US Endowment representing the re-allocation of nonstructural panels

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Table 3: X_rw % of total roundwood (softwood/hardwood) in a region converted to a primary wood product, p

In addition, users are given the option to override the default values with their own numbers as long as they add up to 100%. For example, users from CA, WA, and OR may want to use specific values that can be derived from TPO data HWP-C-vR/HWP Data/ExistingData at main · jeremygroom/HWP-C-vR · GitHub and found in the Harvested Wood Products Model V.r (HWP Data Visualization).

Product

At the product level embodied carbon results are presented based on the users selected products and quantity and then summed. A carbon factor is also calculated representing the ratio of product embodied carbon divided by the amount of carbon stored in the product.

Total Embodied Carbon

Eq EC-1:

EC_t (CO₂)=Σ(EC_p*Mp)

Where:

EC_p = Embodied Carbon Product p (kg CO2)/unit product p

M_p = User inputted material product p

5.12 Embodied Carbon Factor (ECF) Calculation

The embodied carbon factor of a product is the ratio of embodied carbon (GWP_FOSSIL) divided by the carbon stored in the product as CO2.

Eq EC-2

ECF_p (dimensionless) = EC_t∕CO₂ storage in product

Where EC_pt = Total Embodied Carbon of a product (kg CO₂e)

CO₂ stored in product (kg CO₂)

5.2 Forest (Log)

5.21 Embodied Carbon Factor by Region Calculation for softwood or hardwood (and sawlog pulpwood if available) (ECFR)

Using the data in Table 3 provided as input into Eq EC-3, an ECF_R is determined for each region, species group (hardwood and softwoods), and roundwood type (sawlog and pulpwood).

Eq EC-3

ECF_R = p=1n( ECF_{p * %RW}rspl)

[Repeated for each Region/Softwood/Hardwood/Sawlog/Pulpwood]

Where Logtype = combination of Region/Softwood/Hardwood/Sawlog/Pulpwood

ECF_p = the Embodied Carbon Factors calculated in Eq EC-2

RW = %of each logtype allocated to each primary product.

R =region (N,S,RM, PC)
Sp = softwood, hardwood
l = log type (sawlog, pulpwood)

EPDs are regularly updated, and therefore future iterations of the tool will seek to incorporate them based on the following criteria:

1. Use a current EPD. Expiration dates are on the declaration page of every EPD. EPDs are valid for 5-years. (See Figure 2)
2. If there are two EPDs from the same region, pick the one that is either the most relevant to the product or has the most representation of the region. Sometimes the LCA report, if available, can provide better transparency.
3. Use an expired EPD if a current one is NOT available and the product category EC value is sought.
4. Use an LCA when an EPD is not available.
5. Use an LCA if increased regional granularity is sought.

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ISO. 2017. Sustainability in buildings and civil engineering works- Core rules for environmental product declarations of construction products and services. International Organization for Standardiza tion. Second edition (ISO 21930:2017-07) 80pp.

U.S. Endowment. 2024. CORRIM Embodied Carbon Tool Progress Report Final Report 12192024

Murray, L.T., C. Woodall, A. Lister, K. Stockmann, H. Gu, Urbanski, S., Riley, K., Greenfield E., et al. 2024. Chapter 5: Quantifying greenhouse gas sources and sinks in managed forest systems. In Hanson, W.L., C. Itle, K. Edquist. (eds.). Quantifying greenhouse gas fluxes in agriculture and forestry: Methods for entity-scale inventory. Technical Bulletin Number 1939, 2nd edition. Washington, DC: U.S. Department of Agriculture, Office of the Chief Economist.

Smith, James E.; Heath, Linda S.; Skog, Kenneth E.; Birdsey, Richard A. 2006. Methods for calculating forest ecosystem and harvested carbon with standard estimates for forest types of the United States. Gen. Tech. Rep. NE-343. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northeastern Research Station. 216 p.

Product Category Definitions

Product Categories Definitions

Lumber softwood = dimension lumber, studs cut from a round log. Conversions based on a nominal 2x6, actual 1.5x5.5

Plywood softwood = softwood veneers bonded together with adhesive and cured under heat and pressure. Veneers are peeled from round log.

Composite Panels under Smith et al.

Particleboard = non structural panels constructed of small particles of wood coated with adhesives and cured under heat and pressure. Wood inputs can be roundwood, chips, timmings and cutoffs, construction waste. Usually softwood species

Medium density fiberboard (MDF) = non structural panels constructed of fine particles of wood coated with adhesives and cured under heat and pressure. Wood inputs can be roundwood, chips, timmings and cutoffs, construction waste. Usually softwood species

Oriented Strand Board = Structural panel made of flakes of wood aligned in particular way, coated with adhesive ,and cured under heat and pressure. Usually made of low density hardwood species but can be made with softwood species.

Hardboard

Fiberboard

Other Industrial Products

Since we had no real definition of this product category, too fill in the blank so we had a 100% allocation over all product categories, we took an average of the values for the known product categories.

Wood Pulp

Fuels and Other Emissions

For the Beta version we used wood combustion based on the CORRIM wood boiler LCI developed by Milota and Puettmann 2017

Terms

Life cycle Assessment-

Environmental Product Declarations-

How to get Embodied Carbon (EC) values from an EPD or LCA report

Every EPD is standardized, to a degree, as there are required sections per ISO 14025 Environmental labels and declarations – Type III environmental declarations – Principles and procedures standard. The “owner” of the EPD has the flexibility to add additional information about the product based on their objectives. Below are some key elements to look for in an EPD.

1. Where possible, EPDs should reflect cradle- to- gate scope, rather than cradle-to-grave. This information should be presented in the Declaration Page (see Figure 2). The EC values can be presented as A1, A2, A3, and Total (A1-A3), though some EPDs just provide the total (A1-A3). Some EPDs reflect cradle to gate with options, or cradle to grave scope. Make sure only the A1-A3 values are transferred and not just the total which might include A4 or A4, and/or to grave (C1-C4). A1-A3 is required on all EPDs.

The EC values in an EPD represent the Global warming potential (GWP) (fossil based), and are annotated asGWP_FOSSIL [kg CO2 eq].

For example, in Table 4 below, the values on the orange line are the EC values that would be entered into the Embodied Carbon database. These values are for Inland Northwest Softwood Lumber .

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Table 4: Example Cradle to Gate LCIA Results for 1m³ of Inland Northwest softwood lumber - Absolute Basis (AWC 2024, INW-EPD-Final2-07222025.pdf)

2. The carbon (C) storage in product values is included in each EPD because biogenic carbon tracking is required (ISO 21930). ISO 21930 follows standard Intergovernmental Panel on Climate Change convention that removals of carbon from the atmosphere are listed as negative values and emissions are positive. Accordingly, ISO 21930 stipulates that biogenic carbon enters the product system as a removal (negative value)(e.g., a log) and leaves the system as an emission in the product and coproducts (positive value). The table below (Table 5) is required in all wood-based EPDs and is normally found after impact indicators (table above) are displayed. Even where the EPD scope is cradle-to-gate, the biogenic carbon will be reported under A1-A3, A5, C3/C4 column headings. The value needed for “carbon storage in product” can be found under the C3/C4 column heading. In the case of Inland Northwest Softwood Lumber, the carbon storage is 863.02 kg CO2e = Biogenic carbon emission from product. This is the carbon stored in the final product.

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Table 5: Example Biogenic Carbon Inventory Parameters for Inland Northwest Softwood Lumber (AWC 2024, INW-EPD-Final2-07222025.pdf)

For Calculating the CO2e in a wood product, using 863.02 kg CO2 as an example, the following steps may be followed. In the spreadsheet, “Embodied carbon data master”, under the tab density_specific gravity_MC find the density of Inland Northwest softwood lumber.

Specific gravities are in columns C-F and densities are in columns G-I. Density increases with moisture content and specific gravity decreases with moisture content.

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For calculating carbon content of wood, use the “oven dry” option and 0% MC density of the product. In this example of Inland northwest softwood lumber, the oven dry density is 470.74 kg/m3. Because wood contains about 50% carbon, 470.74 kg/m3 of softwood lumber contains about 235.37 kg/m³ of carbon.

To compare the carbon storage in wood to the carbon emissions released (EC), wood carbon must b econverted to CO₂ by multiplying the carbon content of the product, 235.37 kg/m3, by the molecular weight ratio of carbon dioxide to carbon which is 44/12. This is expressed as:

235.37 kg/m3 X 44/12 = 863.02 kg of CO2 in the product.

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