Biochar Carbon Removal in Concrete and Soil: Six Crediting Methodologies Compared, and the Case for Rules Written for Built Materials

Biochar is increasingly embedded in concrete and other building materials, yet most crediting rules for biochar carbon removal were written for soil. This paper applies six methodologies—Verra VM0044, Isometric, Puro.earth, Global Biochar C-Sink, BioCarbon BCR0011, and the EU certification methodology under Delegated Regulation (EU) 2026/285—to one reference biochar used in agricultural soil and in structural concrete in Kaohsiung, Taiwan, and compares the tonnage each credits, the conditions and deductions each applies, and the market access each provides. Four of the six methodologies credit concrete exactly as they credit soil, extending soil decay models to a matrix in which the processes those models describe are largely absent. Credited storage in concrete ranges from 1.9 to 3.0 t CO₂ per tonne of biochar under durability horizons of 100, 200, or more than 1,000 years that cannot be compared directly. Temperature corrections derived from soil incubations are applied to products, and the EU parameter table ends at 25 °C, below the annual mean of southern Taiwan and major Southeast Asian cities. Deductions for mix-design changes, rules on claiming the same tonne in a product's carbon footprint, and the treatment of risk after incorporation differ in ways that can lead to over-crediting or double claiming. The paper recommends a persistence basis for built materials separate from soil models, temperature parameters that cover tropical climates or are not applied to embedded uses, disclosure on common horizons, full accounting of mix-design changes, and explicit rules on product claims. Supplementary files: a Python script that reproduces Table 1 and the sensitivity cases, and the resulting CSV table.