A New Story Above Your Garage in Redwood City
We assess structural load before design begins — so your budget reflects actual site conditions.
Above-Garage ADU Construction vs. Interior Garage Conversion
These are two different projects, and this page covers one of them.
Garage ADU construction means building a new habitable unit that uses your garage as its structural base — either above it or on the same footprint. A garage conversion is something else: turning the existing interior of your garage into living space without adding a story.
This page covers new construction — specifically, the kind of project where a livable unit is built on top of or around an existing garage, requiring engineering, fire separation, and a structural assessment before a single line is drawn. If you only want to know whether your garage interior can become a bedroom or studio without major structural changes, that's our garage conversion page.
The distinction matters because the scope, cost, and permit path are genuinely different. Knowing which one fits your property is the right place to start.
Licensed by the CSLB under CA #1119304 — active & publicly verifiable.
Why Limited Lot Space in Redwood City Makes Above-Garage ADUs Worth Considering
Lots in this part of San Mateo County tend to be modest in size, and setback requirements on the rear and sides eat into the buildable area quickly. On a standard Redwood City parcel, there may not be enough remaining lot coverage — the percentage of a parcel that can be occupied by structures — to add a freestanding unit.
That's where the garage footprint becomes valuable. It's already counted in your lot coverage calculation, so building above it adds habitable square footage without consuming new ground area — a practical advantage specific to this market.
Here's what most homeowners don't realize: the garage position matters. Detached garages set back from the main house — common in older Redwood City neighborhoods like Stambaugh-Hanna and the Farm Hill area — are often the cleanest candidate for an above-garage unit. There's no shared wall with the primary residence to engineer around.
What a Structural Assessment Revealed Before an Above-Garage ADU in San Carlos
A structural load assessment — an engineering review of a garage's foundation, posts, beams, and framing to confirm it can carry added weight — is the first step on every above-garage project we take on. We were evaluating a detached garage in San Carlos. The homeowner had researched floor plans and had a layout in mind. From the curb, the garage looked solid — good siding, decent roof.
When we opened the framing on the preliminary review, we found 2×4 wall studs at 16 inches on center — the original spec for a single-story garage, not engineered to carry a second story. The foundation was a standard four-inch slab with no perimeter footing sized for vertical load transfer, and the posts above the garage door were point loads sitting on that slab with no bearing hardware below them. None of that was visible from the curb.
Before any design work started, a structural engineer was brought in. The report confirmed the framing needed reinforcement and the foundation required a perimeter footing upgrade at three corners. That added scope — but the homeowner knew about it before a permit was filed, not after a plan-check rejection three months in. The ADU was completed and rents at market rate. The foundation work added time early; it saved more time and cost later.
Structural Load Review Before Design — On Every Above-Garage Project
We evaluate existing garage structures for load capacity before any design work begins — reviewing foundation type, footing depth, wall framing dimensions, header spans, and post bearing points before a floor plan is drafted. If the structure can carry a second story as-is, we confirm that in writing. If it needs an upgrade, the scope and cost are identified at the outset, before any design dollars are committed.
The alternative is designing a floor plan, paying for Title 24 documentation, submitting to San Mateo County, and then receiving a plan-check correction letter flagging a structural deficiency that was always there. That correction cycle adds weeks; the engineering rework adds cost. Both are avoidable.
Front-loading the structural assessment means the permit submission is complete and the scope reflects what the project actually requires.
Fire Separation, Engineered Footings & the CBC Requirements That Apply
California Building Code Section R302 requires specific fire-rated assemblies between any garage and the habitable space above it. Here's what that means in practice for an above-garage build.
How We Build an ADU Over an Existing Garage
Structural Diagnostics
We start with an on-site review of the existing garage — foundation type, footing condition, wall framing dimensions, header spans, and roof structure. A licensed structural engineer is brought in on any project requiring upgrade confirmation. That report drives the design scope.
Design, Permitting & Build
Once the structural scope is confirmed, our in-house team produces the full permit package — site plan, floor plans, elevations, structural details, Title 24, and the fire-separation assembly specified in the drawings — submits to San Mateo County, and manages plan check. Every upgrade, framing, fire-rated assembly, rough MEP, and finish is performed by our own 25-person licensed crew under CA #1119304, with no phase routed to outside subs.
Final Inspection & Certificate of Occupancy
Before occupancy, every above-garage ADU goes through the required sequence — framing, MEP rough-in, insulation and energy, and final — each coordinated directly with San Mateo County. The certificate of occupancy is issued before the project closes.
Above-Garage ADUs Across the Mid-Peninsula Corridor
Above-garage construction suits lots in the 5,000–7,000 sq ft range that leave limited ground area for detached structures. Each project is assessed individually against current San Mateo County zoning — lot coverage, height, and setbacks confirmed for the specific parcel before design begins.
Converting the garage interior instead of building up? See our garage conversion page.
Above-Garage ADU Questions Homeowners Ask First
You won't know from a visual inspection alone. Wall stud dimensions, footing depth, post bearing hardware, and header spans all have to be evaluated on-site. We conduct a structural diagnostic before any design begins — that review determines whether the existing garage can carry a second story as-is, or whether foundation and framing upgrades are needed first.
Yes. Above-garage ADU construction triggers a full building permit with structural engineering review. San Mateo County's plan check requires stamped structural drawings, a CBC Section R302 fire separation plan, Title 24 energy documentation, and foundation details. It's a more complex submission than a straightforward interior conversion.
The garage remains usable as a garage. The fire separation requirement — Type X drywall on the garage ceiling and common walls, plus a self-closing fire door if there's direct access — is applied to the surfaces between the two spaces. It doesn't eliminate the garage; it regulates how the two occupancies are separated.
Timeline depends heavily on the structural scope. If the existing garage needs foundation upgrades, that work precedes design finalization. In general, projects in Redwood City and San Mateo County run six to ten months from initial structural assessment through final inspection — accounting for the plan-check cycle, correction rounds, and construction sequencing.
Setback requirements apply to the structure as modified. In most San Mateo County jurisdictions, ADUs built above existing garages may qualify for reduced setback standards under California's ADU reform laws — but only if the garage footprint isn't being expanded. We confirm setback eligibility for your specific parcel before design begins.
Request an On-Site Structural Review
The right starting point for an above-garage ADU is a structural assessment — not a floor plan. We'll confirm whether the structure can support a second-story ADU, what the engineering scope looks like, and what the permit path involves — before any design dollars are spent.