Attic insulation in Redwood City

Redwood City is proud of its weather; the city's About page puts the average at 255 sunny days a year. Mild weather is easy to live with, and it hides weak attics: a house can go years with thin insulation before anyone notices the bills or the drafts. This page covers the code, the permit rule, the city's mix of house styles and the hillside edges.

Zone 3: the existing level decides

Redwood City is in Title 24 climate zone 3, the same zone as San Francisco and the bayside cities. Zone 3 treats existing insulation more generously than the warm South Bay zone does. When an attic ceiling is altered:

• below R-19 now, the 2025 Energy Code asks for R-49, covers on recessed cans, and attic ventilation;
• at R-19 or more, it asks only for attic ventilation;
• the zone 3 row has no air-sealing requirement.

That means some Redwood City attics already meet the code. It doesn't mean they're comfortable. Air leaks around lights, pipes and the hatch still let heat escape on cool nights and let attic heat in on the warm days. Our quote names the R-value it aims for, so you can weigh it against the code minimum. The Title 24 page has the full zone 3 row and its exceptions.

Craftsman, Spanish Revival, ranch: three different attics

The city's Residential Design Guide (July 2021) describes the architectural styles found in Redwood City, and three of them shape attic work in very different ways.

Craftsman and bungalow houses. The guide notes that these often include conditioned attic space with dormer windows, the classic one-and-a-half-story bungalow. A finished room under the roof leaves small unfinished pockets behind short knee walls and above the ceiling, each needing insulation and a proper air barrier. These houses are also the ones most likely to have old wiring, which we refer to an electrician before insulating. Our guide to insulating older Bay Area homes covers what to expect.

Spanish Revival houses. The guide describes low-pitched tile roofs or flat roofs with parapets. A flat or near-flat roof can leave a very shallow cavity, sometimes too tight to work in. We check what's reachable and say plainly if the answer is "only from above at reroof time," which is roofing work we don't do.

Ranch and split-level houses. Long, low roofs with moderate eaves give the most workable attics; the guide notes split-levels are often built on hillsides. Low roof pitch at the eaves is where insulation most often blocks the vents, so we install baffles before blowing.

The Census Bureau's 2019–2023 estimates fit that picture: about 22% of Redwood City's housing units date from the 1950s, 11% from the 1940s and 8% from before 1940, with a median year built of 1968. If the walls are as empty as the attic, wall insulation is a separate line we can quote.

The permit rule in the city's own words

The Building Division's FAQ answers "When is a building permit required?" in one line: a building permit is required for all work not specified in CBC 105.2. It gives fences 7 feet and under, painting, flooring and similar finish work as examples of the exempt items, and refers you to the full section. Section 105.2 of the Building Code lists things like small sheds, low walls, finish work and portable appliances. Insulation isn't on it.

Because the city doesn't name insulation, we don't treat the question as answered. Ask the Building Division's Permits counter for your scope. The written quote says who handles the permit, settled before work starts.

Wildfire: check the viewer

The Redwood City Fire Department's wildfire page says the city includes areas with elevated wildfire risk because of vegetation, open space and wind that carries embers, and points residents to the State Fire Marshal's viewer to look up an address. The state's 2025 Local Responsibility Area maps show small zoned areas at the city's hillside edges, with most of the city unzoned. The fire department's own advice for hardening a home starts with ember-resistant vents and Class A roofing; ember-resistant vents are the attic part of that list, and the wildfire insurance guide covers what insurers ask about.

Who supplies the power

PG&E delivers electricity and supplies gas in Redwood City. Generation comes from WestLight Energy, which was called Peninsula Clean Energy until July 1. WestLight's rebates cover heat pump water heaters and HVAC, used EVs and e-bikes; insulation isn't among them. See the rebates page.

How a Redwood City job runs

Redwood City is where Attic WISE is based. The inspection is free, or you can send photos or video instead. You get a photo report, then a written quote with the R-value and depth for each measure. Nothing is installed before you sign, and you have 5 business days to cancel. The cost page shows Bay Area market ranges.