Brock Commons Tallwood House
An 18-storey hybrid mass timber student residence at the University of British Columbia. Tallest mass timber building in the world at the time of its occupancy in August 2017. The most thoroughly documented mass timber LCA in the public domain.
- Owner
- University of British Columbia
- Architect
- Acton Ostry Architects Inc.
- Tall wood advisor
- Architekten Hermann Kaufmann ZT GmbH
- Structural engineer
- Fast + Epp
- CLT & glulam supplier
- Structurlam Products
- LCA practitioner
- Athena Sustainable Materials Institute (Matt Bowick, author)
- Storeys / GFA
- 18 / 15,120 m²
- Use
- Student residence (404 beds)
- Completion
- August 2017
- Certification
- LEED Gold
- LCA standard
- EN 15978:2011, 100-yr study period
- Awards
- Wood Design & Building, Canadian Wood Council; multiple international citations
The published numbers
Two public documents anchor the disclosed environmental performance of this building. The first is the Athena Sustainable Materials Institute Environmental Building Declaration (EBD), authored by Matt Bowick, dated January 2018, conducted in conformance with EN 15978:2011. The second is the Canadian Wood Council case study published the same year, which summarises a separate carbon overview attributed to the project team.
From the Athena EBD — 100-year whole-building life cycle
| Indicator (EN 15978) | Disclosed value | Source |
|---|---|---|
| Global warming potential, 100 yr | 29,900,000 kg CO₂e | EBD Table 2, p. 5 |
| Per gross floor area | 1,977 kg CO₂e / m² | Derived from EBD |
| Stratospheric ozone depletion | 0.108 kg CFC-11 eq. | EBD Table 2, p. 5 |
| Acidification (land + water) | 184,000 kg SO₂ eq. | EBD Table 2, p. 5 |
| Eutrophication | 43,000 kg N eq. | EBD Table 2, p. 5 |
| Fossil fuel depletion | 65,900,000 MJ surplus | EBD Table 2, p. 5 |
From the Canadian Wood Council case study — wood-specific carbon overview
| Item | Disclosed value | Source |
|---|---|---|
| Volume of CLT + glulam used | 2,233 m³ | CWC case study, "Carbon overview" |
| Carbon stored in wood (biogenic) | 1,753 tCO₂e | CWC case study, "Carbon overview" |
| Avoided GHG emissions (substitution) | 679 tCO₂e | CWC case study, "Carbon overview" |
| Total claimed "carbon benefit" of using wood | 2,432 tCO₂e | CWC case study, "Carbon overview" |
Note on apparent inconsistency. The Athena EBD reports the 100-year whole-building GWP at 29,900 tCO₂e — a figure that includes operating energy, all materials, replacements, and end-of-life processing. The Canadian Wood Council case study separately publishes a 2,432 tCO₂e "carbon benefit" attributed to the wood structure alone. The two figures appear in different documents addressing different boundaries and are not contradictory; they are simply addressing different scopes. The DRL recomputation below operates on the wood-structure figure because that is the disclosure where the biogenic-carbon convention does most of the work.
What the disclosure excluded, in the disclosure's own words
Three points in the Athena EBD define the boundary of the disclosed numbers. They are reproduced here so the reader can verify them against the source.
On module B1 (installed product in use)
"B1: there is currently insufficient consensus in terms of methodology and data to practically quantify these effects for all products used in the building." — Athena EBD, p. 13, on excluded modules
On the EN 15978 standard's treatment of biogenic carbon
EN 15978:2011 — the standard the EBD was conducted under — treats biogenic carbon under what is commonly called the "biogenic-zero" or "carbon-neutral" convention. Sequestration in growing wood is reported as a negative emission at production stage (A1–A3); the same amount is then reported as a positive emission at end of life (C3 or C4). The net contribution of biogenic carbon to the building's GWP is therefore zero by convention, regardless of what physically happens to the wood at end of life or in the forest after harvest.
On end of life (Modules C2–C4)
"This assessment assumes that once the material is either [1] separated for recycling, reuse, or energy recovery purposes or [2] disposed of (i.e. either via landfill or incineration), it has reached its end-of-waste state." — Athena EBD, p. 14, on the polluter-pays allocation
On forest-side processes
The EN 15978 product-stage module A1 — "raw material supply" — encompasses, in the assessment's own description, "primary resource harvesting and mining" (EBD Table 6, p. 13). The standard does not require, and the EBD does not include, accounting for soil organic carbon dynamics in the harvested stand, nor for the foregone sequestration of the forest that would otherwise have continued growing. Those quantities are outside the assessment boundary by design of the standard.
Three liabilities outside the disclosed boundary
From the boundary statements above, three specific carbon flows are demonstrably outside the scope of what was disclosed. The DRL framework adds them back:
- Soil organic carbon (SOC) efflux following clear-fell harvest. Empirical loss in the top 30 cm of soil over the first 5–10 years post-harvest. Outside A1 by standard.
- End-of-life methane from the fraction of mass timber that enters landfill rather than being recovered. EN 15978 assumes preferred end-of-life scenarios; real-world C&D waste streams do not always match.
- Foregone sequestration — the carbon the forest would have continued to accumulate over the 100-year reference period had the trees not been felled. Outside the goal-and-scope of EN 15978; explicitly so.
The three liabilities added back
Each of the three liabilities is calculated from the building's disclosed timber volume of 2,233 m³, multiplied by an emission factor sourced from peer-reviewed literature. The biogenic-storage and substitution-credit lines use the building's own disclosed values rather than recomputed ones — the recomputation does not silently restate what was published. The factor values shown here are mid-range defaults; the calculator below lets the reader substitute low- or high-range alternatives.
| Line | Factor or source | Result | Source |
|---|---|---|---|
| Timber volume (CLT + glulam) | 2,233 m³ | — | CWC case study |
| A1–A3 manufacturing emissions | 0.18 tCO₂e / m³ | +402 tCO₂e | Athena EPDs, FPInnovations |
| Biogenic carbon stored (building's own disclosure) | — | −1,753 tCO₂e | CWC case study |
| Substitution credit (building's own disclosure) | — | −679 tCO₂e | CWC case study |
| Disclosed net (using their numbers) | — | −2,030 tCO₂e | A1–A3 minus disclosed credits |
| + DRL liability 1: SOC efflux | 0.12 tCO₂e / m³ | +268 tCO₂e | James & Harrison 2016 |
| + DRL liability 2: EOL methane | 12% biogenic C as CH₄ | +2,134 tCO₂e | Ximenes 2008; IPCC AR6 GWP100 |
| + DRL liability 3: foregone sequestration, 100 yr | 0.95 tCO₂e / m³ | +2,121 tCO₂e | Stephenson 2014; Searchinger 2023 |
| Full-boundary total (wood-attributable) | — | +4,925 tCO₂e | Recomputed |
| Delta vs. disclosed | — | +6,956 tCO₂e | From −2,030 to +4,925 |
The disclosed "carbon benefit" of using wood at Brock Commons is reported as a 2,432 tCO₂e credit (the sum of 1,753 tCO₂e biogenic storage and 679 tCO₂e substitution credit, both quoted from the public case study). Under full-boundary accounting that includes SOC efflux, end-of-life methane, and 100-year foregone sequestration at mid-range factor values, the wood-attributable contribution becomes a 4,925 tCO₂e liability. The swing is approximately 6,956 tCO₂e — almost three times the size of the original disclosed credit. At the EPA average of 4.6 tCO₂e per passenger vehicle per year, this is approximately 1,513 vehicle-years of emissions.
The bigger frame. The Athena EBD reports total 100-year building GWP at 29,900 tCO₂e. With the wood-attributable swing of +6,956 tCO₂e added, the corrected 100-year GWP is approximately 36,856 tCO₂e — about 23% higher than disclosed. This is a wood-line correction only. The concrete podium, foundations, steel components and operating energy are not recomputed here; they will appear in the corresponding concrete and steel ledger entries.
A note on what this recomputation does not say. It does not say wood is worse than concrete. The concrete alternative — Brock Commons' counterfactual concrete equivalent, or the 30 Hudson Yards class of buildings in this same ledger — also has uncounted liabilities. The point is that the published headline for this building, as written, omits material flows that are documented in peer-reviewed literature. Bringing the disclosure up to a full boundary is what auditors call closing the books.
Run the math yourself
The calculator below is preloaded with the disclosed timber volume from the public case study. Every emission factor is a dropdown — change any one and the recomputation refreshes. If you believe a factor is wrong, change it and see what the corrected number becomes.
Sources cited on this page
- Bowick, M. (2018). Brock Commons Tallwood House, University of British Columbia: An Environmental Building Declaration According to EN 15978 Standard. Athena Sustainable Materials Institute. naturallywood.com/wp-content/uploads/Tallwood_House_Environmental_Declaration_20180608.pdf
- Canadian Wood Council (2018). Brock Commons Tallwood House — UBC Vancouver Campus: The advent of tall wood structures in Canada. A case study. cwc.ca
- EN 15978:2011 — Sustainability of construction works — Assessment of environmental performance of buildings — Calculation method. European Committee for Standardization.
- Stephenson, N. L., et al. (2014). Rate of tree carbon accumulation increases continuously with tree size. Nature, 507(7490), 90–93. nature.com/articles/nature12914
- Luyssaert, S., et al. (2008). Old-growth forests as global carbon sinks. Nature, 455(7210), 213–215.
- James, J. & Harrison, R. (2016). The effect of harvest on forest soil carbon: a meta-analysis. Forests, 7(12), 308.
- Achat, D. L., et al. (2015). Quantifying consequences of removing harvesting residues on forest soils and tree growth — a meta-analysis. Forest Ecology and Management, 348, 124–141.
- Mayer, M., et al. (2020). Tamm Review: Influence of forest management activities on soil organic carbon stocks: A knowledge synthesis. Forest Ecology and Management, 466, 118127.
- Ximenes, F. A., et al. (2008). Greenhouse gas balance of native forests in New South Wales, Australia. Carbon Balance and Management, 3(1), 1–13.
- Wang, X., et al. (2013). Methane emissions from landfills: Measurements in a Florida unlined landfill. Waste Management.
- IPCC (2021). Climate Change 2021: The Physical Science Basis. Working Group I contribution to the Sixth Assessment Report, Ch. 7, Table 7.15 — methane GWP₁₀₀ = 27.9.
- Searchinger, T. D., Peng, L., et al. (2023). Re-evaluating the climate effects of biofuels and bioenergy and the role of land use. Nature, 619, 64–73. doi.org/10.1038/s41586-023-06187-1