Home Additions & ADU in Redwood City - One Fixed Price, Permits Handled

Fast, Reliable Home Additions & ADU Across Redwood City

Home additions in Redwood City typically run $45,000 to $130,000, and detached ADU construction usually lands between $90,000 and $220,000 depending on site conditions, and that number can shift fast if your lot sits on bay fill. If you live in Redwood Shores, your project will almost certainly need deep piers or pile foundations before framing starts, which is something a contractor with no local experience often misses until the budget is already blown. We have been building additions and ADUs across Redwood City long enough to know exactly where the surprises hide on your street, and we also handle our Roofing in Redwood City. Call (877) 610-1318 when you are ready to talk about your lot.

Call (877) 610-1318

Why Barrett & Sons Construction Is Redwood City’s Preferred Home Additions & ADU Company

Tom Barrett puts his name, address, and license number on every contract and every page we publish. Look us up. Ask around the neighborhood. The crew showing up at your door in Redwood City is Tom’s sons and their teams, not a rotating cast from an out-of-state call center. Every permit gets pulled and every inspection gets signed before we call the job done, because the permit inspector works for you, not for me, and that is the way we like it. There are plenty of owners in ZIP 94063 and 94064 who have been burned by a phone quote that did not survive first contact with reality. We put scope, allowances, and change orders in writing, and nothing changes price until you have signed off on it.

We have operated owner-first since 1998, and Redwood City has been part of our Peninsula service area for years. Dispatch and scheduling for Redwood City jobs is coordinated from our San Francisco Bay Area office, and the crew members who show up are background-checked, uniformed, and carrying the Barrett & Sons name on their shirts. The 90-Day Done Right Promise is written on every contract, not tucked into fine print: if something is not done right, one call brings Tom back to make it right.

Our Home Additions & ADU Services in Redwood City

ADU Design & Permitting

Redwood City has its own ADU rules layered on top of California state law, and the permitting path in the Redwood Shores portion of ZIP 94065 is slower and more geology-heavy than a typical flatland lot in 94063. We handle the design work, the soils assessment, the permit package, and the inspections as one scope, so you are not coordinating three different companies. A detached ADU in Redwood City typically runs $90,000 to $220,000 all-in.

Garage Conversion ADU

Many of the post-WWII ranches and bungalows in central Redwood City have detached or attached garages that were never built to living-space standards, and the seismic retrofit required to convert one properly is real work. We convert existing garage shells into permitted ADUs, and this route usually lands between $30,000 and $80,000 in Redwood City depending on whether the foundation and electrical panel need full replacement, which they often do on 1950s-era slabs. This is the fastest path to a rentable unit on properties where the lot cannot absorb another structure.

New Detached ADU

On lots in 94061 and 94064 with the side or rear yard to spare, a new detached ADU gives you a clean floor plan and modern energy performance without inheriting someone else’s framing problems. On conventional Peninsula soil, this is straightforward construction. In Redwood Shores, the same square footage requires pile-supported foundations, which is a line item you need to see in writing before the first shovel hits dirt. We price that honestly on the front end.

Junior ADU & Interior Conversion

A junior ADU built inside an existing home footprint is often the only realistic option on Redwood City’s smaller central lots, where setbacks and lot coverage rules leave no room to build out. We convert existing living space, basements where present, or oversized garages into code-compliant JADUs. Interior conversions in Redwood City frequently run into the same flatland reality we see across the Peninsula: original stucco, outdated subpanels, and shallow concrete perimeter foundations that should be addressed before walls come down.

We also build Home Additions & ADU projects of every size across the Peninsula, and our team regularly works alongside our Kitchen Remodeling in Redwood City and Bathroom Remodeling in Redwood City crews when an addition expands into those spaces.

Trusted Brands We Service in Redwood City

When we install Windows & Doors - Redwood City on an addition, we are putting in names you can look up: Simonton, Ply Gem, and PGT, depending on the exposure and energy requirements of the wall. Builders in Redwood Shores know that bayfront salt air eats standard hardware faster than the warranty assumes, so we spec stainless fasteners and marine-grade flashing on those jobs as a matter of course, not as an upgrade pitch. We order directly for each project, so what we quote is what arrives, on the truck, with paperwork.

Common Home Additions & ADU Problems We See in Redwood City Homes

• Out-of-level slabs in Redwood Shores. Slabs poured in the 1980s on the original bay-mud fill have frequently moved an inch or more out of plane from differential settlement. Framers called in for what looks like a simple addition often discover the existing floor is not level by any construction standard, and foundation remediation has to happen before a single new stud goes up.
• Shallow perimeter foundations on 1940s-1960s ranch homes. The core flatland neighborhoods in 94063 and parts of 94061 are full of post-WWII wood-frame homes with original stucco and concrete foundations never designed for a second story. Adding an upward addition without a seismic evaluation is a gamble we will not take with your family’s home.
• Salt-air corrosion on bayfront properties. In Redwood Shores, the persistent salt-laden air off the Bay corrodes Simpson ties, metal flashing, and HVAC components faster than standard specifications account for. Any addition there needs corrosion-resistant hardware specified from day one, not discovered during a five-year inspection.
• Outdated subpanels that cannot carry the new load. A 1950s-era electrical panel in central Redwood City was not built for a modern ADU with a heat pump, induction range, and EV charger. We include panel upgrades in the written scope when the load calculation says they are needed, so the price change is on paper before it hits your wallet.

Pricing for Home Additions & ADU in Redwood City, CA

We Also Serve Cities Near Redwood City

Our crews regularly work in Redwood City and the surrounding Peninsula communities. If you are in San Carlos, Woodside, Menlo Park, or North Fair Oaks, the same local knowledge and in-writing pricing apply, and we are close enough that a site visit is never a scheduling struggle. No trip charge inside the county.

FAQs - Home Additions & ADU in Redwood City