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Redwood City · Garage Conversion
Make that Redwood City garage a permitted, livable ADU.
The shell already stands, which makes a conversion the cheapest ADU you can build here — once we deal with the slab, the egress, and the seismic detailing the old garage never had.
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Garage Conversion in Redwood City — fast facts
City
Redwood City
ADU type
Garage Conversion
Contractor license
CSLB #1119373
Free estimate
(916) 677-9774
Last updated
Why a conversion pencils out
The costly parts are already built
A garage conversion wins on price for a blunt reason. You already bought the shell. Walls standing, roof on, a slab in the dirt — we're not pouring a foundation or framing a whole building from scratch. On the Peninsula, where a detached unit of the same size can run into the high six figures, that gap is enormous. I've turned a detached garage behind a Mount Carmel bungalow into a 514 sq ft one-bedroom without disturbing the main house at all. The honest part: a garage was built to park a car, not to house a person. The old shell hides things you can't see from the driveway. We open it and look before anyone signs a number.
Reuses the existing slab, walls and roof — no new foundation poured
Cheapest path to a permitted ADU on an expensive Redwood City lot
An old structure hides surprises — we investigate before we quote
The slab decides the budget
That slab was poured for a car
Here's what gets glossed over. A garage slab is sized for a vehicle, not a bedroom — usually un-rated concrete on shallow footings, no insulation under it, pitched toward the old door so rain runs back out. None of that flies for a habitable room. So a real conversion often means underpinning those footings, or pouring a fresh slab with thickened edges to carry the walls and give you the level, insulated floor a dwelling needs. Redwood City sits near the region's active faults, so any new foundation work here gets engineered for real ground motion, not dropped in casually. We core the slab, check the footings, and shoot the floor for slope before the proposal — because the slab is the one line that keeps a conversion cheap or blows it up.
Un-rated slab on shallow footings — often needs underpinning or a new pour
Old drain slope corrected to a level, insulated, code floor
New foundation work engineered for Peninsula seismic loads
The opening and the code
Closing the door, hitting code
The change everyone notices is the garage door itself. That opening becomes a real wall — framed, insulated, sheathed, with windows set where a dwelling needs light and air. Done right, nobody walking down the block reads the building as a former garage. Then the part you don't see. Insulation in walls and a roof that were bare. A ceiling height that clears the habitable-room minimum, which on older low garages is its own headache. And a bedroom egress window or door sized so a person can climb out in a fire. California dropped the old rule that forced you to replace the garage parking you remove — a quiet change that killed a deal-breaker on tight Redwood City lots. We build to current code, not to whatever the garage happened to be.
Old garage-door opening framed into an insulated wall with windows
Insulation, ceiling height and egress brought up to habitable code
California removed the replacement-parking requirement — a win on tight lots
Lot lines, utilities, the city
Fire walls, PG&E and city review
A few Redwood City specifics shape a conversion before tools come out. If you're converting a detached garage that hugs the property line — normal on these tight Peninsula lots — code can demand fire-rated walls on the sides facing the neighbor, which adds assembly and cost. Power is PG&E. The unit needs its own circuits, often a panel touch, and a meter on PG&E's unhurried timeline. And the City of Redwood City runs your permit, plan check, and inspections. Fees are high, review is stricter and slower than inland, and on the hill parcels in Emerald Hills or Farm Hills the ground steepens enough to push a conversion toward hillside foundation work. We check the lot line, the terrain, and the utility runs on the first visit.
Detached garage near the lot line can trigger fire-rated walls
PG&E circuits, possible panel upgrade and a meter on a slow timeline
City of Redwood City permits — high fees, strict and slow review
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The most common things Sacramento homeowners ask before starting an ADU project.
Fair question, and I won't dodge it. We're a Sacramento design-build contractor, and Redwood City is about a two-hour drive west of our home base. We extend out to the Peninsula for owners who want our craftsmanship and our pricing over a Bay Area quote, and for jobs big enough to be worth the road. A conversion sits on the smaller end, so I'll be straight: if it's a simple, clean garage and rock-bottom price is the only goal, a Redwood City-local builder might pencil tighter once you back out the travel. Where we earn the drive is the conversion that turns structural — new slab, seismic foundation work, a hillside parcel in Emerald Hills — because that's exactly the kind of fixed-price design-build job our crew handles cleanly.
Usually, yes — and on the Peninsula those savings are worth chasing hard. You already own the slab, the walls, and the roof, which are the most expensive pieces of any build. A conversion reuses all three, so it commonly lands well under a detached unit of the same footprint. The word "usually" carries weight, though. A garage was never built to be lived in, and Redwood City adds wrinkles a flat inland lot doesn't: a slab that may need reworking for seismic, fire-rated walls if the garage sits near a line, slow and pricey city review, steeper ground in the hills. Those narrow the gap. We open the structure, look hard at the slab and the bones, then tell you whether the conversion stays the cheap option or whether something else actually serves you better.
Probably nothing wrong for a car — that's the whole problem. A garage slab is poured for vehicle weight, not a habitable room. It's typically un-rated concrete on shallow footings, no insulation beneath, and pitched toward the old door so rain drains out. A bedroom can't sit on that as-is. Depending on what we find, a real conversion means underpinning the footings, or pouring a new slab and thickened edges to carry the new walls and give you a level, insulated, code floor. In Redwood City there's an extra layer — any new foundation work gets engineered for the region's seismic loads, not just floated in. We core the slab and shoot the floor for slope before pricing, because the slab is the single biggest variable in a conversion budget.
It does, anywhere the structure or its foundation gets touched. The Peninsula sits close to the region's active faults, and older garages were rarely built with serious seismic detailing. So when a conversion involves a new slab, new footings, or reframing walls, that new work gets engineered for real ground motion — anchored to the foundation, with shear and hold-downs where the building needs them. A conversion doesn't always mean tearing into the foundation, and when the existing slab genuinely works we keep it and say so. But waving off seismic in Redwood City would be malpractice. We design the work to the geology, not around it.
No — and that change matters a lot on a tight Redwood City lot. California removed the old requirement that forced you to replace the off-street parking a garage conversion eliminates. There was a time you'd convert the garage and then have to carve a new parking pad out somewhere on the lot, which on a cramped Peninsula parcel was often the thing that killed the project outright. That requirement is gone for ADU conversions in most situations. So the garage becomes a dwelling without you scrambling to rebuild parking you no longer have room for. It's a quiet law change, and it's exactly why a lot of conversions that used to be impossible on these narrow lots now actually work.
It becomes a wall — a real, finished, insulated exterior wall, framed where the door used to roll up, with windows set into it so the room gets the light and ventilation a dwelling needs. Done right, the building stops reading as a converted garage; it just looks like a small house. That opening is also where a lot of the energy-code and egress work concentrates, since we're building a whole new insulated wall assembly from scratch rather than upgrading an existing one. We'll usually set the bedroom egress window in that new wall too. On a Redwood City conversion the design of that street-facing wall matters for how the unit reads against the bungalow neighborhoods, so we draw it to fit the block, not fight it.
Maybe — it depends on how close the garage sits to the property line, and Redwood City lots are tight enough that this comes up often. When a structure is within a certain distance of the lot line, the code requires fire-rated wall assemblies on the sides facing the neighbor, to slow fire spread between properties. A detached garage tucked near a side or rear line is the classic case. That rating adds materials and labor to those specific walls. It's not a dealbreaker, but it's real cost you want in the number from the start, not discovered mid-build. We measure the setbacks on the first visit and tell you exactly which walls, if any, need the rated assembly so the quote reflects it.
With the City of Redwood City. Redwood City is its own incorporated city, so your conversion permit, plan check, and inspections all run through the city's building and planning departments — not San Mateo County. One counter. The catch is the one every Redwood City owner meets: the city is ADU-friendly in policy but slow and strict at the counter in practice. Fees run high, review takes longer than an inland owner expects, and on a hill parcel the structural picture adds scrutiny. A conversion of an existing structure can be a cleaner path through review than a ground-up build, but only if the package is complete. We confirm zoning, terrain, and the structural picture on the first visit so the submittal is built for Redwood City from day one.
Often yes, but the terrain changes the job. Redwood City runs from the bayfront flats up into the hills, and parcels in Emerald Hills and Farm Hills steepen enough that foundations stop being a simple slab question. A garage on a sloped lot may sit on a stepped or hillside foundation, and any new structural work has to account for grade, drainage, and how loads travel down the hill — on top of the seismic engineering the whole region needs. That's more design and more cost than a flat lot in Friendly Acres or Centennial. It's also exactly the kind of structural conversion where a fixed-price design-build crew earns its place. We read the slope on the first visit and price what the hill actually demands.
On the Peninsula, more than almost anywhere. Bay Area ADU economics are a different planet from Sacramento — detached units here commonly run $400K to $750K and up, and rents are far higher than inland, which is precisely why the numbers still pencil for owners in this market. A conversion is the cheapest way in, since you reuse the shell. So you get a high-rent unit on high-value land at the lowest construction cost of any ADU type. The cost still swings on what we find — slab, seismic, fire-rated walls, hillside grade. We open the structure, core the slab, measure setbacks, read the terrain, then write a fixed price so the number you sign is the number you pay.
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Every Sacramento ADU project is different. Here are the other paths we build under one roof — and we're happy to talk through which one fits your lot best.
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PaulOwner · Future Generation
9 min read2,025 words8 sections
Converting a Garage Into an ADU in Redwood City — A Straight-Talk Guide for Peninsula Owners
A garage conversion is the cheapest way into an ADU, because the structure you'd otherwise pay to build is already standing. That's the pitch, and it holds up. But a garage was never meant to be lived in, and Redwood City layers on things inland lots don't — active faults nearby, a slow and pricey city counter, hillside parcels where the ground steepens, narrow lots where a garage near the line triggers fire-rated walls. This guide is about converting one here specifically. We're a Sacramento builder who extends out to the Peninsula, so I'll be honest about the drive and about where a conversion stays the smart, cheap move.
01Section
What a garage conversion actually is
A garage conversion takes a structure you already own — an attached or detached garage — and turns it into a permitted, legal dwelling. The footprint exists. The walls exist. The roof exists. Rather than building a new structure, we change the use of one that's already there, which is why it's the cheapest and usually the fastest ADU type. You aren't paying for a new foundation, roof, or exterior shell. You're paying to make an existing box livable.
That's the line that separates a conversion from the other two ADU types. A detached ADU stands free, poured and framed from dirt up. An attached ADU bolts new conditioned space onto your house. A conversion keeps the shell and rebuilds the inside and the systems to dwelling standards. All three are legitimate ADUs under California law — they just cost and build very differently, and conversion sits at the affordable end of that spread.
