Mill Valley adds carbon-free concrete to city code

Mill Valley is adding a carbon-free concrete requirement as it fine-tunes its green building code.

“Tonight the city of Mill Valley took bold climate action,” Mayor Max Perrey said after the City Council backed several updates on Tuesday.

“Decarbonizing our built environment is imperative to addressing climate change, ensuring clean air and protecting human health and our environment,” said Perrey, who advocated for the carbon-free cement on behalf of the Sierra Club before he was elected to local office.

Mill Valley follows the county and Sausalito with the concrete requirement, although it will only apply to construction projects using more than 13 cubic yards of cement.

Vice Mayor Caroline Joachim said the ordinance “is actually tailored and reasonably so, and there are exemptions.”

“It’s smart with the 13 cubic yards threshold,” she said.

Low-carbon concrete uses recycled glass and other industrial waste and does not produce climate-changing greenhouse gases. It is available in Marin and not more expensive, city planners said.

The requirement was among several updates to clarify and readopt Mill Valley’s green building standards. These rules, which cover energy infrastructure and building materials, were revised last August to comply with 2025 statewide legislation raising construction industry standards.

California’s green building thresholds give property owners some flexibility with choosing materials and supplies for remodeling and construction. These elements are individually graded. Overall, projects must fall under state-set energy efficiency and sustainability targets.

Across Marin, most cities and towns have fine-tuned their codes to satisfy these state thresholds while being mindful of local conditions.

The cement ordinance’s 13 cubic yard threshold, for example, exempts smaller projects such as replacing a small driveway. Several council members said projects of that scale would have minimal impact on reducing the reliance on materials whose emissions contribute to atmospheric climate change.

The other “flex path” clarifications given first-reading approval on Tuesday involve standards for electrical panels, duct sealing, raised floor insulation and heat pump water heaters. The updates also concern “electric vehicle readiness,” which involve installing wiring and conduits for charging systems in remodels and new construction.

Grace Ledwith, the city’s sustainability coordinator, said the ordinance updates are in line with similar standards in other Marin municipalities.

Mark Chhabria, a county sustainability analyst, said the building community — architects, suppliers, contractors — has sought that uniformity.

“What we hear from them, more than anything, is what you’re proposing is reasonable to ask builders to comply with,” he said, “but we want it to be the same across Marin County.”

The code updates generated praise.

“As Mill Valley expands its housing stock and deploys Measure L funds for infrastructure and buildings, it can substantially mitigate climate impact through the use of low-carbon concrete,” Al Grumet and Marilyn Price of Sustainable Mill Valley wrote in a letter.

“As we know, climate action is more than reducing vehicle miles traveled,” former planning commissioner Greg Hildebrand told the council.

“Building material alternatives, decarbonization and electrification provide critical solutions,” he said. “And it is time for the design and construction industry to step up and help us achieve projects built above building code minimum standards.”