Home Additions & ADU in South San Francisco - One Fixed Price, Permits Handled

Fast, Reliable Home Additions & ADU Across South San Francisco

A home addition in South San Francisco typically runs $53,100 to $153,400, while a full ADU construction lands between $106,200 and $259,600 depending on whether you’re converting a garage, building detached, or adding a junior unit inside your existing footprint. Those are honest numbers for this market, and they reflect what we see on permits, plans, and actual construction here, not a national average pulled from a spreadsheet.

Call (877) 610-1318

We’ve worked in the 94080 and 94083 zip codes long enough to know the difference between a Sunshine Gardens rancher on a pier-and-post foundation and a Sign Hill cottage with knob-and-tube wiring. Tom Barrett lives twenty minutes away, and his sons run the crews. When you call our Home Additions & ADU team, you’ll speak to someone who knows what your specific block looks like. Call (877) 610-1318 for a free estimate.

Why Barrett & Sons Construction Is South San Francisco’s Preferred Home Additions & ADU Company

We’ve been doing this since 1998, and we’re not a franchise dispatching strangers from two counties over. Tom Barrett’s name, address, and license number are published, so you can look them up before you sign anything. When we tell a South San Francisco Roofing homeowner we’ll be there Tuesday at 7, the crew shows up Tuesday at 7, and they’re background-checked, uniformed, and carrying our name.

South San Francisco customers have seen us pull permits on every eligible job and stand in front of inspectors we’re happy to see. The permit inspector works for you, not for me, which is exactly why I like him. Every scope change, every allowance, every price adjustment arrives as a written change order before a single nail moves. The allowance that isn’t on paper is a surprise waiting for a date. And every completed job carries our 90-Day Done Right Promise, written on the contract, not buried in fine print. If it’s not done right, Tom comes back and makes it right, one call. That’s the whole promise.

Our Home Additions & ADU Services in South San Francisco

Homeowners in South San Francisco call us for everything from a modest room bump-out to a full detached ADU in the backyard. Here’s how we approach the four most common projects.

ADU Design & Permitting

South San Francisco’s planning department has its own set of ADU standards, setbacks, and parking requirements, and they’ve tightened and loosened those rules over the years. We handle the full design set, structural calcs, and permit submittal so you don’t have to decode municipal code. In 94083 particularly, we’ve guided homeowners through rear-yard setbacks on hillside lots where the grade change makes a standard ADU plan unworkable without adjustments. Permits pulled and inspections signed on every eligible job, because the last contractor most of our South San Francisco customers used told them permits were optional.

Garage Conversion ADU

A garage conversion in South San Francisco typically lands between $35,400 and $94,400, depending on whether we’re working with an attached 1950s single-car or a larger detached structure. Many of the post-war garages in Sunshine Gardens and Buri Buri sit on slabs with no insulation, no moisture barrier, and zero seismic anchoring. We address all of that before the drywall goes up. If you’re planning to convert the garage and also want the main house refreshed, we also handle Kitchen Remodeling in South San Francisco, so you can sequence the work without juggling two contractors.

New Detached ADU

Building a detached ADU in South San Francisco costs $106,200 to $259,600 all-in, but the site determines a lot. On the eastern flatlands near the biotech campuses, the bay mud under your lot may require deep pilings or a mat foundation, which adds real cost and time. A contractor who’s only built in Burlingame will consistently underbid that foundation work. We won’t. We spec the geotech report first, price the foundation honestly, and give you a written line-item quote before you commit to anything.

Junior ADU & Interior Conversion

A JADU, which is an interior conversion typically under 500 square feet, is the fastest and least expensive way to create legal rentable space in South San Francisco. These projects often mean converting an existing bedroom, a portion of the living space, or an underused utility room into a self-contained unit with its own entrance, kitchenette, and efficiency bathroom. Because many of the ranch homes here were built with the kitchen and bath on opposite ends of the house, the plumbing tie-ins can get interesting. We’ve handled enough of them to know what the inspector is going to flag before he arrives. If you’re opening walls anyway, talk to us about Bathroom Remodeling in South San Francisco as part of the same permitted scope, it saves money and one round of inspections.

Trusted Brands We Service in South San Francisco

Our Windows & Doors - South San Francisco team installs products from Simonton, Ply Gem, PGT, and CGI because these are brands you can look up, not mystery products off a van. On an ADU or room addition in South San Francisco, the window package matters more than most homeowners expect, especially on west-facing walls that catch the wind coming off San Bruno Mountain. We stock common sizes and hardware locally for faster turnaround on South San Francisco projects, and if a PGT impact window or Simonton sash shows up wrong from the factory, we handle the replacement so you’re not stuck chasing a manufacturer’s warranty line. You’ll know the material names in your scope before we order them, in writing.

Common Home Additions & ADU Problems We See in South San Francisco Homes

• Pier-and-post foundations on 1940s and 1950s bungalows. Most of the older stock in Sunshine Gardens and Buri Buri sits on cripple walls that were never seismically bolted. Any addition that ties into that foundation needs retrofitting first, or you’ll be paying for cracked drywall inside five years. We bring the bolt schedule to the permit office before we pour a thing.
• Deep bay mud on the eastern flatlands. The redevelopment zone near the biotech campuses sits on soft bay mud. Standard spread footings aren’t adequate, and we’ve seen bids from out-of-area GCs that don’t account for pilings or mat foundations. Ours does, because we’ve dug there. Careful with the wind, too, the stretch along 101 through South San Francisco accelerates marine air in a way that delays crane work and rips tarp off open framing.
• Salt-laden air and fog eating fasteners. Homes in South San Francisco sit between bay air from the east and coastal fog from the west. Exposed fasteners, metal flashing, and unpainted trim corrode faster here than in San Mateo. We spec corrosion-resistant hardware on every exterior connection, especially for sunrooms and enclosed patios where metal meets wood. It’s a small line item that prevents a much larger one later.
• Knob-and-tube wiring and galvanized supply lines in Sign Hill cottages. The pre-war Craftsman and cottage stock on the older hillside blocks routinely still has original knob-and-tube wiring hiding in walls and galvanized plumbing that’s rusted from the inside. When you open walls for a room addition or JADU, you need an electrical plan and a plumbing plan in the same permit set. We don’t let that become a surprise change order mid-project.

Pricing for Home Additions & ADU in South San Francisco, CA

We Also Serve Cities Near South San Francisco

Our crews work in San Bruno, Daly City, Millbrae, and Visitacion Valley, so if your project sits just over the city line, the same team can handle it. We coordinate scheduling and dispatch from our San Francisco Bay Area office, and crews serve South San Francisco locally. Wherever the job is, the permits are pulled, the change orders are written, and the 90-Day Done Right Promise applies.

FAQs - Home Additions & ADU in South San Francisco