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California Enacts Tough Rules for New Glasshouses

Chris Beytes

It might be old news if you’re a California grower, but it'll be shocking news to the rest of the country—that is, if your state decides to follow California’s lead: The Golden State, effective January 1, has introduced new requirements for greenhouses aimed at increasing their energy efficiency and thus reducing their energy use.

Called 2022 Title 24, Part 6, the code section’s most obvious requirement is that ALL new greenhouse construction in the state must feature two layers (or more) of glazing (note: this only applies to NEW construction).

“Whether glass or acrylic or poly film, you have to have two or more layers separated by an air barrier,” said Nadia “Dr. Greenhouse” Sabeh, PhD, who spoke on the topic at the National Greenhouse Manufacturers’ Spring Meeting in San Diego recently.

That means double poly is fine and twinwall polycarbonate is fine, but glass is not unless you install two layers of glass. And what about energy curtains?

California does NOT allow the use of energy curtains in lieu of that second layer of glass. Why not? Because you can open and close them as you desire.

“What the energy commission’s stance is, they want energy efficiency measures that can be built in to the infrastructure—so they can look at the design and say, ‘Okay, this structure is made of double glass,’” Nadia explained. They don’t want the grower to be able to manipulate the energy systems—they want the system to be a permanent, unchangeable part of the structure.

In addition, there’s not enough real-world California-based data to argue in their favor—which is something stakeholders are hoping to be able to present to California decision-makers in the future to perhaps change their minds.

Another part of the rule requires that all heating, cooling and ventilations equipment must comply with all application requirements for equipment associated with HVAC systems. This is not likely to be an issue, as most all commercial equipment already meets such requirements (but beware of discount equipment purchased overseas).

Greenhouse lighting is also addressed in the new code, and most current HPS lighting and all LED lighting should meet the requirements, at least for now.

But the big question is: Why is California suddenly so interested in greenhouse energy use?

Well, it’s not just greenhouses—it’s also indoor farms, and yes, cannabis did have something to do with putting controlled environment agriculture on the radar. But Nadia assures us that California is looking at the energy use of EVERY industry and horticulture was never going to escape their scrutiny. Plus, what grower doesn’t want to reduce energy costs? I don’t know of one!

I did a 30-minute video interview with Dr. Greenhouse. In addition, she has a blog post on the subject at her website ( plus plenty of resources. Go to the “Education” tab—it’s the first item under that. GT   

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