Free written scope consultation - allowances, timeline, and change-order rules on paper before a single trade is scheduled
Before
After
Before
After
Before
AfterFast, Reliable Home Additions & ADU Across Atherton
When a homeowner in Atherton starts planning an addition or ADU, they’re usually not wondering *if* the town will scrutinize the plans. They’re wondering how many rounds of review it’ll take. We know the drill here because we’ve been through it enough times to recognize the patterns: the arborist report that flags a 200-year-old oak 30 feet from the proposed foundation, the neighbor’s engineer asking about sight lines from a second story, the building department’s request for moment-frame calculations because the San Andreas Fault sits just ten miles west. A home addition in Atherton typically runs $45,000 to $130,000, and a detached ADU from $90,000 to $220,000. Call (877) 610-1318 for an estimate that accounts for the town’s reality, not a generic price sheet.
Why Barrett & Sons Construction Is Atherton’s Preferred Home Additions & ADU Company
Tom Barrett started Barrett & Sons in 1998, and his name has been on the trucks ever since. In Atherton, where half the battle is navigating the town’s discretionary review process, that matters more than in most places. We don’t hand your project to a rotating cast of subcontractors; Tom’s sons run the crews, and most days you’ll see one of them on site. When a neighbor’s engineer submits comments on your addition during the 90-day review window, Tom picks up the phone himself. He’s heard the same objections before and knows which ones the town takes seriously.
Atherton customers can verify everything about us before signing. Tom publishes his name, address, and license number, and any homeowner can look them up. Every eligible job includes permits pulled and inspections signed. Every change order arrives in writing before work proceeds. And every contract carries the 90-Day Done Right Promise: if it’s not done right, one call brings Tom back. You won’t find that from a regional outfit that treats Atherton as just another stop on the Peninsula route.
Response time to Atherton is straightforward: dispatch and scheduling run from the San Francisco Bay Area office, and crews serve Atherton locally. When you call, a live person answers, 24/7. Not a voicemail box, not an out-of-state call center.
Our Home Additions & ADU Services in Atherton
Here’s what our Home Additions & ADU team actually does in town, and how Atherton’s rules shape the work.
ADU Design & Permitting
In Atherton, design and permitting aren’t a formality; they’re the whole game. The town has one of the most meticulous building departments in San Mateo County, and the Heritage Tree Ordinance means a proposed ADU footprint often gets redesigned after the arborist report comes back. We prepare plans with that in mind from the first draft, not as a surprise we discover in month three. A junior ADU or detached unit in Atherton routinely runs $90,000 to $220,000 depending on foundation work, utility runs, and how many times the discretionary review window gets extended.
Garage Conversion ADU
Plenty of Atherton estates built before 1960 still have detached carriage houses or oversized garages that were never meant to be lived in. Converting one means upgrading the original foundation, often replacing galvanized plumbing, and sometimes dealing with knob-and-tube wiring that’s been hiding behind those stucco walls for 70 years. A garage conversion in Atherton typically runs $30,000 to $80,000, and the town will want structural calculations before it’ll sign off on the permit. We pull the permit, schedule the inspections, and make sure the inspector signs off before we call the job done.
New Detached ADU
Building a new detached ADU on a one-acre Atherton lot is a full construction project. We’re talking new foundation, new utility trenching, new subpanel, seismic moment frames, and Atherton Roofing that looks like it belongs on the estate rather than bolted on as an afterthought. The Heritage Tree Ordinance applies here, and so does the neighbor-review process; adjacent estate owners routinely retain their own engineers to comment on submitted plans. A new detached ADU in Atherton runs $90,000 to $220,000, and the site prep and utility work can be a project within the project.
Junior ADU & Interior Conversion
A junior ADU, whether it’s a converted wing of the main house or a reworked interior space above the garage, is the most budget-friendly path in Atherton. It also carries the fewest structural touchpoints with the Heritage Tree Ordinance. Costs range from $45,000 to $130,000 depending on whether you’re reconfiguring an existing footprint or adding square footage. Interior conversions here often reveal the same pre-1960s surprises: original foundation systems and wiring that were fine in 1955 but aren’t up to today’s code for a separate living unit.
What happens when you call
- 1
A real person answersNo phone trees - you reach a local pro.
- 2
You get an upfront price rangeHonest numbers before anyone is dispatched.
- 3
A background-checked tech heads outLicensed & insured, dispatched right away.
- 4
You approve before work beginsNothing starts until you say go.
Trusted Brands We Service in Atherton
When your Atherton addition calls for Windows & Doors in Atherton, we’re likely reaching for Simonton or Ply Gem units, depending on the elevation and the architectural character of the house. PGT impact windows come up on the estates closer to the fault line, where a homeowner wants the extra engineering without changing the look of a mid-century ranch. We keep straightforward access to local parts and materials in the Bay Area, so a window order that would take a regional outfit three weeks doesn’t stall your project’s inspection schedule. The point is simple: materials you can look up, not mystery brands off a van.
Common Home Additions & ADU Problems We See in Atherton Homes
- Heritage tree conflicts. A mature coast live oak or redwood can’t be moved, and in Atherton it usually can’t be removed without a fight. We’ve watched foundation placements shift a dozen feet sideways after the arborist report lands, which is why we bring the arborist in early instead of waiting for the building department to ask.
- Pre-1960s wiring and plumbing. Much of Atherton’s original housing stock still runs on knob-and-tube wiring and galvanized pipe. When you open a wall for an addition, code requires you to bring the whole exposed system up to current standards, which changes the scope and the price. We put that in the written change order before any work happens.
- Seismic retrofitting requirements. Ten miles from the San Andreas Fault is not the place to skip moment frames. The town’s building department expects structural calculations on virtually every addition permit, and an inspector who works for you, not for us, will be the one signing off.
- Neighbor review delays. Atherton neighbors on adjacent estates regularly retain their own architects or engineers to formally comment on submitted plans. An addition that sails through plan check in Palo Alto can sit in Atherton’s 90-day discretionary review window multiple times. We factor that into our scheduling from day one, so you’re not standing on a half-finished foundation wondering what’s taking so long.
Pricing for Home Additions & ADU in Atherton, CA
A home addition in Atherton runs $45,000 to $130,000. A detached ADU runs $90,000 to $220,000. A garage conversion runs $30,000 to $80,000, and a junior ADU or interior conversion lands in that $45,000 to $130,000 range. What moves the number isn’t a mystery: foundation work on a pre-1960s house, utility trenching across a one-acre lot, arborist-mandated redesigns, and how many rounds of town review the plans go through all shift the final figure. We give you that figure in writing before we start, and if anything changes, you’ll see a written change order before a single nail moves. Call (877) 610-1318 to schedule a free estimate, and we’ll walk the property with you first.
We Also Serve Cities Near Atherton
Our crews also cover Atherton and the surrounding Peninsula communities: North Fair Oaks, Palo Alto, Stanford, and East Palo Alto. If you’re just over the town line on the North Fair Oaks side, or your project spans a property near the Stanford boundary, the same team that knows Atherton’s building department will handle your job. We also handle Kitchen Remodeling in Atherton and Bathroom Remodeling in Atherton for homeowners who want the whole estate brought up together.
Serving Atherton, CA - Our Local Coverage Area
We’re based in the Atherton area and know this community well. Use the map below to see our service coverage - if you’re nearby, we can almost certainly help.
FAQs - Home Additions & ADU in Atherton
A home addition in Atherton typically runs $45,000 to $130,000, with the final number tied to foundation condition, seismic requirements, and how much the Heritage Tree Ordinance shapes the footprint. Older pre-1960s homes carry extra costs for wiring, plumbing, and structural upgrades that code requires once walls are opened. Call (877) 610-1318 for an exact quote, estimates are free.
Expect the town’s discretionary review window to take up to 90 days per round, and a complicated project can sit through it more than once. After permits clear, construction on a detached ADU in Atherton typically takes six to ten months, depending on the scope of foundation and utility work. We’ll give you a written schedule before we start, and we’ll keep it updated as the town weighs in.
Yes. Every eligible job we do in Atherton includes permits pulled and inspections signed, because the last contractor most customers used tried to tell them permits were optional. In Atherton, that approach doesn’t survive first contact with the building department, and we’d rather hand you the signed inspection card than a story.
Atherton is purely residential, with every lot at minimum one acre, and the town’s Heritage Tree Ordinance plus neighbor-review culture adds review time that adjacent cities rarely see. Foundation placements routinely get redesigned after arborist reports, and adjacent estate owners often file formal comments on submitted plans. We schedule for that reality from the first day, so your project isn’t stalled by surprises. Call (877) 610-1318 to talk through your specific lot.
Every completed job carries our written 90-Day Done Right Promise, which is on the contract, not buried in fine print. If something isn’t done right, Tom comes back and makes it right, one call. That promise holds whether your project is a garage conversion off Mountain Home Road or a second story addition near the Menlo Circus Club.
Ready to Plan Your Addition or ADU in Atherton?
Call (877) 610-1318 to schedule a free estimate. Tom Barrett will walk the property with you, talk through what the town will expect from the plans, and give you a written scope and price before anything starts. If you already have a written estimate from another outfit, bring it in and we’ll give you a free second opinion. Homeowners in Atherton don’t need the cheapest bid; they need a name they can verify and a contractor who answers his own phone.
Written by Tom Barrett, Owner at Barrett & Sons Construction, serving Atherton and the surrounding Peninsula since 1998.