Choose your city to see which California Title 24 climate zone your project sits in, and what that single number changes about insulation, glazing, roofing and ductwork.
Nothing here is a quote, a bid, an engineering determination or a boundary determination. We are a drafting and design firm: we coordinate with a licensed structural engineer and a Licensed Land Surveyor when your project needs one, rather than performing or stamping that work ourselves.
The state is carved into 16 Title 24 climate zones, and the boundaries follow ZIP codes rather than city or county lines. The zone is the very first thing an energy calculation needs, because it determines which weather file and which heating and cooling loads the software works from. Change the zone and the insulation, glazing performance and roofing requirements all move with it.
Our service area covers two of them. Santa Clara County's valley floor and the bayside mid-Peninsula — San Jose, Sunnyvale, Santa Clara, Campbell, Mountain View, Palo Alto, Redwood City, San Mateo among them — fall in Zone 4, which is mild but has a genuine cooling season and applies a prescriptive ceiling on solar heat gain. Fremont, Newark and the seaward side of San Mateo County sit in Zone 3, cooler and more marine, where the cooling load is light enough that the prescriptive SHGC limit drops away.
The southern end of the area is the part worth being careful with. Morgan Hill, Gilroy and Hollister sit inland where a city can span more than one zone, and getting the zone wrong does not produce a slightly optimistic model — it produces the wrong model. For those addresses we read the zone off the parcel before anything is calculated, and this tool tells you that rather than printing a number it cannot back up.
Treating the city name as the answer. Zones track ZIP boundaries, and more than one city here crosses a line. San Jose alone is big enough that the eastern foothills and the valley floor do not always behave identically in the model. We run every report off the project address.
Ordering glass before the zone is settled. Zone 3 generally imposes no prescriptive solar heat gain ceiling, so clear high-transmittance glazing is fair game. Place the same order in Zone 4, where an SHGC cap does apply, and the prescriptive package fails — leaving you to change the glass or model the whole building.
Assuming a hillside or South County parcel behaves like a valley one. Los Altos Hills, Woodside and the Gilroy and Hollister end of the area all sit outside the tidy flat-valley assumption. Confirming the zone before the window schedule is drawn costs nothing; finding out at plan check costs a resubmittal.
Settle the zone and everything downstream follows from it. We register and produce the Title 24 CF1R energy calculations, then reconcile them against the permit set, so nothing in the fenestration schedule, the R-value callouts or the mechanical notes contradicts the report by the time it reaches a reviewer.
By ZIP code — not by city limits and not by county. The mapping from postal code to zone comes from the California Energy Commission, and the compliance software reads it to pick the weather data every subsequent number depends on. Several cities here sit across a boundary, so we verify it from the project address itself.
Because anything it said would be a guess. Morgan Hill, Gilroy and Hollister sit where the mapping is not consistent across the city, and the wrong zone cascades into a wrong energy model, wrong insulation callouts and a report the window schedule cannot match. Telling you to confirm it against the CEC map for your address is more useful than a confident number that turns out to be wrong.
Fremont sits in Zone 3, kept cool by bay and marine air, with a light summer cooling load and generally no prescriptive cap on solar heat gain. San Jose sits in Zone 4, warmer in summer, with an SHGC ceiling applied to windows and glass doors. Identical code, different prescriptive targets.
No. They are the values you would typically be aiming at, which is enough to shape a design and price materials. The actual demonstration happens on a registered certificate for your particular building, under whichever code cycle is current the day you apply, and the city decides what it will take.
It does. Everything the zone produces — insulation levels, glazing performance, how reflective the roof has to be, what the ducts need — has to appear on the sheets and agree with the certificate. Reviewers read the two documents against each other, and a disagreement between them is one of the most frequent reasons a set comes back.
Residential or commercial, drafting or Title 24 — send a few details and we'll follow up with next steps and a free quote.
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