How full-boundary accounting works.

What DRL adds

The current standards — EN 15978, ISO 21930, and the national building-LCA standards built on top of them — exclude three specific carbon flows from the disclosure boundary for timber products. The DRL framework adds them back. The three flows are: soil organic carbon efflux following clear-fell harvest; end-of-life methane from the fraction of mass timber that enters anaerobic landfill conditions; and foregone sequestration — the carbon the standing forest would have continued to accumulate had the trees not been felled. Each flow has a peer-reviewed measurement basis. Each has a defensible range of emission factors. The recomputation does not require any new science; it applies measurements that already exist in one part of the regulatory apparatus to the part that does not currently use them.

What gets added back, and from where

Liability 1 — Soil organic carbon (SOC) efflux

Clear-fell harvest disturbs soil to a depth of 30+ cm. Soil organic carbon, accumulated over decades of forest growth and root turnover, oxidises and leaves the soil over the following 5–10 years post-harvest. Meta-analyses of post-harvest soil-carbon trajectories give a mean loss of approximately 11% of soil organic carbon in the top 30 cm — though the range across studies is wide.

Translated to per-cubic-metre-of-harvested-timber units, using typical mass-timber-grade plantation yield (~250 m³/ha), the SOC efflux factor falls in the range of 0.06 to 0.20 tCO₂e per m³ of harvested timber. The DRL mid-range default is 0.12 tCO₂e/m³.

Sources: Achat et al. 2015 (Forest Ecology and Management 348:124–141); James & Harrison 2016 (Forests 7(12):308); Mayer et al. 2020 (Forest Ecology and Management 466:118127).

Liability 2 — End-of-life methane

EN 15978 and the Environmental Product Declaration regime treat biogenic carbon under what is called the "carbon-neutral convention" — sequestration is reported as a negative emission at production stage, and the same amount is reported as a positive emission at end of life. In aggregate over the building's full life cycle, biogenic carbon nets to zero. The convention assumes that the end-of-life pathway is dominated by combustion (CO₂ release) or recovery (no release). In practice, a substantial fraction of mass timber in construction and demolition waste in North America enters landfill, where anaerobic decomposition produces methane.

Methane has a 100-year global warming potential of 27.9 (IPCC AR6 WG1, Table 7.15). Measured fractions of biogenic carbon released as methane from wood in landfill conditions range from 3% (IPCC default, assumed-best-case) through 12% (Ximenes 2008, measured Australian landfill) to 18% (Wang 2013, long-term decay). The DRL mid-range default is 12%, applied as:

EOL methane (tCO₂e) = biogenic_carbon_stored × 0.12 × (16/44) × 27.9

where the (16/44) converts CO₂-equivalent biogenic-store mass into CH₄ mass, and 27.9 is the GWP100.

Sources: Ximenes et al. 2008 (Carbon Balance and Management 3(1):1–13); Wang et al. 2013 (Waste Management); IPCC 2021 AR6 WG1 Chapter 7 Table 7.15.

Liability 3 — Foregone sequestration

The carbon a forest would have continued to accumulate had the trees not been felled. This is, technically, an opportunity cost — the difference between the harvested-and-replanted trajectory and the keep-growing trajectory. It is excluded from EN 15978 because EN 15978 is a product-system standard, not a landscape-system standard. The standing forest is outside its scope.

Stephenson et al. (Nature 2014, 403 species confirmed) established that large trees continue accumulating carbon at accelerating rates as they age — overturning the prior assumption that mature forests are net-neutral. Luyssaert et al. (Nature 2008) established that 75% of stands over 180 years old remain net carbon sinks. Searchinger and Peng (Nature 2023) and the subsequent Nature 646 exchange documented the magnitude of the convention error at global scale: 3.5–4.2 GtCO₂e per year undercount.

Translated to per-cubic-metre-of-harvested-timber units, the foregone-sequestration factor depends on the assessment window chosen. The DRL defaults are: 0.45 tCO₂e/m³ for a 50-year window; 0.95 tCO₂e/m³ for a 100-year window (matching the EN 15978 reference study period); 2.00 tCO₂e/m³ for a 200-year window. The 100-year window is the default for whole-building LCA recomputation. The 50-year window is appropriate where the harvested wood is from beetle-killed salvage (as for T3 Minneapolis on the Corrected Ledger) and would have decomposed regardless.

Sources: Stephenson et al. 2014 (Nature 507:90–93); Luyssaert et al. 2008 (Nature 455:213–215); Peng/Searchinger/Zionts/Waite 2023 (Nature 620:110–115); Sohngen/Baker/Favero 2025 critique and Searchinger/Berry/Peng reply (Nature 646:E18–E23).

How a recomputation runs, line by line

The recomputation for any single timber building follows a fixed sequence. The inputs are: harvested timber volume in m³; the building's disclosed biogenic-carbon storage in tCO₂e (where published); and the building's disclosed substitution credit in tCO₂e (where published). The outputs are seven lines:

1. A1–A3 manufacturing emissions = volume × A1-A3 factor (default 0.18 tCO₂e/m³, range 0.13–0.25 from Athena and FPInnovations EPDs).
2. Biogenic storage (industry credit) = the building's own disclosed value where published; otherwise volume × 0.917 tCO₂e/m³ (EN 15978 convention factor).
3. Substitution credit = the building's own disclosed value where published, otherwise zero.
4. Disclosed net = A1-A3 − biogenic storage − substitution credit. This is what the disclosure would show.
5. + SOC efflux = volume × SOC factor (default 0.12 tCO₂e/m³).
6. + EOL methane = biogenic storage × 0.12 × (16/44) × 27.9.
7. + Foregone sequestration = volume × FS factor (default 0.95 tCO₂e/m³, 100-yr window).

The full-boundary total is the sum of A1-A3 plus the three liability lines. The delta is the difference between the full-boundary total and the disclosed net — the magnitude of the boundary error.

Every emission factor in the arithmetic is sourced. Every recomputed building on the Corrected Ledger applies this same arithmetic. Each one has an embedded calculator that lets the reader change any input and see the recomputed number; each one carries a downloadable Reproduction Sheet with the arithmetic shown line by line. Any third party can replicate any number on this site.

Scope notes

The DRL framework is, at present, a methodology for recomputing the wood-attributable portion of building-level emissions. Three things are explicitly outside its scope:

1. It does not recompute non-wood components of the building (concrete podium, steel reinforcement, glazing, MEP). Those use their own published emission factors. A complete whole-building corrected number would apply DRL to wood and the existing factors to the rest.
2. It does not say wood is worse than concrete. The concrete alternatives have their own uncounted liabilities — primarily, the embodied carbon of the cement they require, against the carbonation re-uptake credit at end-of-life. A full-boundary comparison across all materials is the policy ask. The recomputed buildings on the Corrected Ledger demonstrate the magnitude of the wood-side error; they do not by themselves settle the material-choice question.
3. It is not a substitution-credit calculator. Where buildings have published substitution credits (T3 Minneapolis: 1,411 tCO₂e; Brock Commons: 679 tCO₂e), the recomputation preserves them as-disclosed and adds the three excluded liabilities on top. The DRL framework does not, in this iteration, take a position on whether substitution credits are appropriately calculated; it accepts them as published and applies the boundary correction independently.

How to check our work

Every recomputation on the site is checkable in three ways. First, the HTML pages on the Corrected Ledger show the arithmetic in a table on the page. Second, the embedded mini-calculator on each building page runs the same arithmetic live — change a factor and watch the answer move. Third, the downloadable Reproduction Sheet (PDF) for each building lays out every input, every factor, every step of the calculation, every citation, with a sign-off line. The three sources are guaranteed to agree by automated testing (the JavaScript calculator and the Python PDF generator are tested against the same canonical numbers; 6/6 verification passed at last build).

If any number on this site is wrong, please submit a correction via the feedback channel. Every submission is logged with timestamp. Substantive corrections result in an updated page and a revision note.