Washington’s attempt to become the first state to limit embodied carbon through its base building code, rather than through a procurement statute, is running behind its own schedule. The Washington State Building Code Council spent an August 25, 2026 work session still negotiating the basic terms of a proposed embodied carbon appendix, with no vote taken, and the broader 2024 code update cycle that would carry the appendix into force has already slipped from a November 1, 2026 effective date to May 3, 2027. For an audience watching California’s CALGreen requirements and the five-state buy-clean procurement wave, Washington’s appendix would open a different front: instead of governing what the state itself buys, it would hand cities and counties an optional, ready-made embodied carbon limit for private construction, the first of its kind proposed through a base model code rather than a standalone green code.
A different mechanism than buy-clean
Washington already requires reduced-carbon concrete, structural steel, reinforcing steel, flat glass, and mineral wool insulation on its own construction projects under the Buy Clean Buy Fair Washington Act (HB 1282), a procurement law in the same family as the statutes California, New York, Colorado, and, since this past July, Minnesota have adopted. What is now before the council, formally proposal 24-GP1-118 and more recently drafted as Appendix S, would go further by reaching private construction through the building code itself. Submitted originally by the New Buildings Institute, the appendix would not be mandatory on its own. It would sit on the shelf as an optional appendix to the state’s adaptation of the International Building Code, available to any city or county that chose to reference it in a local adopting ordinance, much as jurisdictions today opt into stretch energy codes.
What the appendix would actually require
The proposal covers new buildings, additions, and alterations above a size threshold that would itself be set by the adopting jurisdiction, bracketed between 50,000 and 100,000 gross square feet. Covered projects would document embodied carbon through one of two structural options the council is still choosing between. Option 1, the broader version, offers three compliance paths: a product-level path requiring Type III environmental product declarations for at least 90 percent of covered materials by mass or volume, with their combined global warming potential held to a bracketed share, among 80, 90, 100, 120, or 175 percent, of industry-average baseline values in a reference table; a whole-building life cycle assessment path measured against an absolute limit of 102 or 92 pounds of CO2 equivalent per square foot (roughly 500 or 450 kilograms per square meter), again at a percentage the adopting authority having jurisdiction (AHJ) selects, or against a functionally equivalent reference building; and a building-reuse path for alterations that retain at least 45 percent of the existing structural frame and envelope. Option 2 drops the product-level path entirely and relies only on the whole-building assessment. Both versions use a 60-year study period, exclude biogenic carbon from counting toward compliance, and require sign-off from a registered design professional.
Why the clock keeps slipping
The appendix is only one piece of a much larger 2024 state code update, and the whole cycle has been pushed back twice. In September 2025 the council set May 15, 2026 as its target for finishing the draft rule filings and said it would look for ways to still hit a November 1, 2026 implementation date. By January 23, 2026 that plan had already given way: council staff told members the implementation date had to move because the legislative session could alter the council’s own code-making authority, and because drafting the required cost-benefit and small-business economic-impact statements needed more time. The council settled on May 3, 2027 as the new implementation target after industry representatives, including the Building Industry Association of Washington, argued that roughly 12 months between final adoption and taking effect was necessary for training and compliance-tool updates. The embodied carbon appendix’s own draft rule, CR-102, went out for public comment through June 12, 2026, and the council was still working through two sets of bracketed amendments to it as of its most recent public session in late August, with Carbon Leadership Forum input on covered-product GWP values still pending formal incorporation into the filing.
The authority fight underneath the technical debate
The delay is procedural, but the underlying dispute is about whether the council should be setting carbon limits at all. The Washington Aggregates and Concrete Association, writing for a coalition of trade groups, argued in comments to the council that embodied carbon reduction is not a health-and-safety matter under the statute that defines the council’s authority, and that global warming potential limits belong in a green code, such as the International Green Construction Code, rather than in the base building code. The coalition pointed to a separate technical work group created under the Buy Clean Buy Fair Washington Act, housed at the Department of Commerce, as the more appropriate venue and called the appendix premature. A group of five state representatives, including Davina Duerr and Beth Doglio, countered in a letter to the council that the appendix complements rather than duplicates that work, extending the state’s own climate commitments from its own buildings to the broader building stock, and noted that the approach draws on California’s Green Building Standards Code, known as CALGreen (Title 24, Part 11 of the California Code of Regulations), which already applies a similar logic at the state level. CALGreen’s own embodied carbon provisions took effect for large nonresidential projects on July 1, 2024 and expanded on January 1, 2026 to cover nonresidential buildings of 50,000 square feet and larger statewide, giving Washington’s drafters a live model to point to even as their own process stalls.
What to watch now
Specifiers and sustainability officers working in Washington should not expect the appendix to affect a project before mid-2027 at the earliest, and even that assumes the council resolves the Option 1 versus Option 2 split and the open bracketed values before the broader 2024 code cycle locks in. Watch for a final council vote on the embodied carbon amendments, which has not yet been scheduled as of this writing, and for whether any city moves to adopt the appendix locally once it clears the council, with Seattle and King County the likeliest early candidates, ahead of the state’s own May 3, 2027 date. Firms already reporting under the Buy Clean Buy Fair Washington Act should treat this as a preview of broader product-level EPD demand rather than a new compliance deadline, and should watch whether the council’s final covered-products table lands closer to the Carbon Leadership Forum’s recommended values or the industry coalition’s preferred, looser thresholds. Teams in other states should read Washington’s stall as a caution: a code-based embodied carbon limit, unlike a procurement statute a legislature can pass in a single session, has to survive a multi-year rulemaking process with its own statutory authority questions, and that process can move slower than the climate targets it is meant to serve.