The design team is comparing a conventional concrete frame with a mass-timber hybrid structure.

Biogenic carbon stored in timber must be reported separately from fossil greenhouse-gas emissions because storage is temporary and depends on responsible forestry and end-of-life conditions. LEED does not simply subtract stored carbon from upfront Modules A1–A3 to create an artificially low initial embodied-carbon result. The project must document sustainable harvesting and include relevant end-of-life Module C impacts so that potential release, recovery, reuse, recycling, or disposal of stored carbon is considered. Biogenic carbon is not ignored, because sustainably sourced mass timber may provide a legitimate climate benefit compared with carbon-intensive structural systems. Separate tracking preserves transparency and prevents temporary carbon storage from being misrepresented as permanent emissions avoidance. Therefore, Option B reflects the appropriate whole-life accounting approach.

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