Attic insulation in Union City

Union City's Building Division does something most city building pages don't: it prints its design criteria in one short list. Climate zone 3. Soils hazard zones east of Mission and west of Union City Boulevard. Wildland-urban interface zone east of Mission Boulevard. Codes: the 2025 California building, energy, fire and green codes. Two of those lines decide most of what an attic job here looks like, so this page takes them in turn.

Climate zone 3: the line that matters is R-19

Union City's single ZIP code, 94587, is in climate zone 3 on the Energy Commission's list, and the city's own building page says the same. In zone 3, Table 9-8 of the 2025 Compliance Manual treats an altered attic in one of two ways:

1. Existing insulation below R-19: R-49 at the ceiling, covers on recessed cans, and attic ventilation.
2. Existing insulation at R-19 or more: attic ventilation, and nothing else on the list.

Zone 3 carries no air-sealing requirement in that table and no cool-roof rule on a steep-slope reroof. The fine print, including the exemptions, is on our Title 24 page.

The threshold makes measurement the first job. At the inspection we check depth in several places, note the type of material, and photograph any spot that's been compressed, disturbed or soaked. If the attic is already at R-19 or more, we say so, and topping it up becomes a comfort decision rather than a code one.

Mission Boulevard as the fire line

East of Mission Boulevard, Union City climbs into the hills, and the Building Division marks that side of the road as its wildland-urban interface zone. In February 2025 the State Fire Marshal released new local-area fire hazard maps, and Union City posted its map for public comment with a council hearing in May 2025. The state's map data shows Moderate and High zones touching the city. Check your address on the state's viewer, linked from the city's page, before you plan.

For an attic in that area, the first question is the vents. Wind-driven embers get into attics through eave, gable and roof vents, and screening or replacing them is the attic-side part of hardening a house. Our page on ember-resistant vents covers the options, and the wildfire insurance guide explains what insurers typically ask for. Vents also matter for the code's own ventilation item: replacing a vent must not cut the attic's net free area, so we size replacements to keep attic ventilation at least where it was.

The housing: mostly 1960 to 1979

The city's 2023–2031 Housing Element counts 10,260 units, 47 percent of the housing stock, built between 1960 and 1979, and only about 1.9 percent built since 2010. That puts a large share of Union City attics at fifty years or more, with original insulation from before the state's first energy code for houses.

Attics of that age tend to share a few traits we plan around:

• Thin original batts, often topped up once and uneven since.
• Recessed lights added later, some of them older non-IC fixtures that need a cover before insulation can go near them; see insulation over recessed lights.
• Ductwork in the attic with taped joints that have let go. Sealing or replacing it is ductwork work, and it's usually worth doing while the attic is open.

If we find old knob-and-tube wiring or loose vermiculite, we stop and refer you to a qualified partner before any insulation work; we don't handle either.

Permits at the Building Division

Union City's Building Division handles permits at its counter in City Hall and, for smaller jobs, by email. The email and mail-in list includes minor plumbing, mechanical and electrical work, water heaters, furnace and HVAC replacements, like-for-like windows and re-roofs that don't add weight. Insulation isn't named on it, and the city doesn't publish a list of exempt work on that page. So we treat the permit as a question for the division: email building@unioncityca.gov (opens in a new tab) or call 510-675-5313 with your scope. The written quote should say who handles the permit, and that should be settled before work starts.

Power, gas and rebates

Ava Community Energy is Union City's default electricity provider, with Bright Choice as the default product for homes. PG&E delivers the electricity and supplies the gas. Neither has an attic insulation rebate open to every homeowner right now; the rebates page tracks them.

How a Union City job runs

We're based in Redwood City and come out for the free inspection, or you can send photos or a video. You get a photo report from the visit and a written quote with each measure, its R-value and its depth. Nothing is installed before you sign, the deposit never exceeds California's cap, and you have 5 business days to cancel. For numbers before anyone visits, the cost page shows Bay Area market ranges.