Berkeley 4.405.1: Low carbon concrete that wins specs

What 4.405.1 actually requires

Berkeley added Section 4.405.1 to CALGreen for residential projects and a mirror 5.405.1 for nonresidential. Each instructs project teams to reduce cement in concrete mix designs by not less than 25 percent using supplementary cementitious materials such as fly ash, slag, silica fume, or rice hull ash. The Engineer of Record can approve a smaller reduction where high early strength or an accelerated schedule is essential. (Berkeley Municipal Code, 2024)

Scope and timing in Berkeley

The rule applies to construction projects within city limits that are subject to CALGreen and is enforced through plan review and permits. The city’s summary page states the 25 percent reduction applies to all such projects, with limited exceptions. (City of Berkeley Green Building Requirements, 2025)

Why this matters to EPDs and specs

Cement is the heavyweight in concrete’s footprint, often responsible for about 88 percent of concrete’s CO2 emissions. That is why trimming cement shows up clearly in a Type III EPD’s A1 to A3 results and helps owners tracking embodied carbon. (Center for American Progress, 2024)

Hitting 25 percent without performance loss

Think of cement like hot sauce on tacos. Great in moderation, overwhelming if you flood the plate. To reach 25 percent and keep finish, pumpability, and set times predictable, pair SCMs wisely, optimize aggregate grading, manage water to cement ratio, and use modern water reducers. Portland limestone cement is a quick win that typically trims concrete CO2 about 10 percent while meeting mainstream specs. (PCA, 2024)

What reviewers expect in submittals

• Mix designs that clearly show the 25 percent cement reduction and each SCM proportion.
• Evidence that performance criteria hold, usually strength histories and standard test results.
• A product specific EPD for the optimized mix to document the new GWP and keep caluclations tidy.
• If claiming the exception, a signed letter from the Engineer of Record with the technical basis.

Edge cases and exceptions

Projects needing high early strength or facing unusual schedule constraints may use less than a 25 percent reduction when approved by the Engineer of Record. Keep the rationale tight and aligned with the code’s exception language. (Berkeley Municipal Code, 2024)

The commercial angle

Teams that arrive with compliant mixes plus current EPDs move through permits faster, avoid embodied carbon penalties in budgeting, and get shortlisted more often on low carbon jobs. Reliable cost averages are hard to pin down because scopes differ, yet the revenue lift from repeat specifiying commonly dwarfs the paperwork.

Bring it together

Treat 4.405.1 as both a design constraint and a sales tool. Lock a 25 percent cement reduction into baseline mixes, publish EPDs for those designs, and keep an exception template ready for true fast track pours. That rhythm keeps reviewers confident and your product landing on more project lists.