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Additions are the biggest residential project most homeowners ever undertake. Here’s when they’re genuinely the right call — and we’ll say plainly when they’re not:
Call (510) 990-9243 and describe your house, your lot, and what you need. We’ll tell you what’s permittable, what it roughly costs, and whether an addition is genuinely your best option.
Six types of additions we design and build.
Extra bedrooms, or a full primary suite with bathroom and walk-in closet. Matched rooflines, siding, and flooring so the addition reads as original construction rather than a bolt-on. Includes the HVAC and electrical capacity work an added bedroom actually requires.
When the lot won’t allow building out, build up. We handle the structural engineering — foundation and shear-wall reinforcement, floor framing, stair placement — plus temporary weather protection while the roof is open. The most complex addition type, and the one where an experienced licensed GC matters most.
A private suite with bedroom, bathroom, and often a separate entry — for parents, adult children, or long-term guests. Built as a permitted addition, or as a JADU/ADU where that path fits your lot and goals better.
Insulated, conditioned, permitted sunrooms that work in January — not a glorified patio cover. Engineered for Bay Area sun exposure and wind, with proper foundations, glazing, and HVAC so the room is usable every day of the year.
Bump-outs and small additions that fix daily friction: a real laundry room instead of the garage, a mudroom by the back door, a pantry off the kitchen, a bathroom where the house is short one. Lower cost, shorter schedule, permitted properly.
For homeowners who need the paperwork path solved: architectural plans, structural engineering, Title 24 energy compliance, setback and lot-coverage verification, and city submittal — prepared in-house and carried through plan check. This is the stage most addition projects stall on.
Don’t see your project? Call (510) 990-9243— we handle it all.
Call (510) 990-9243 and talk to Ray or the project team. We ask about your house, lot size, what you need to add, and your budget comfort — and give you a realistic working range plus an early read on whether your lot allows it.
Free in-home visit. We check setbacks, lot coverage, foundation, roof structure, panel capacity, and where plumbing can reach. Then plans and structural drawings are prepared, and you get a written itemized quote — plans, permits, foundation, framing, every trade, finishes, timeline — before submittal.
We submit to the city and manage plan check. Construction runs in order: excavation and foundation, framing, roof tie-in, rough trades, inspections, insulation and drywall, finishes — with the existing house protected and weather-sealed at every stage. Final inspection sign-off means your new square footage is legal and appraisable.
Realistic timeline: plans and permitting typically 3–6 months in most Bay Area cities — additions take longer than conversions; construction 3–6 months depending on size and whether it’s single or second story.
What you won’t pay for:
Call (510) 990-9243 with your square footage target and whether it needs plumbing.
Additions are priced per square foot in conversation and per line item in contracts — and the gap between those two things is where homeowners get burned. Our structure:
Phone range first. Square footage you want to add, single or second story, and whether it includes a bathroom — that’s enough for a working range.
Free feasibility visit and written quote. No fee. And if your lot won’t support the addition you’re imagining, you’ll hear that at the visit, not after you’ve paid for plans.
Five things drive the price on any Bay Area room addition:
Based in Hayward, building additions across the East Bay and South Bay:
Core service area: Hayward · Castro Valley · San Leandro · Fremont · Union City · San Jose
Also serving: Palo Alto · Mountain View · Sunnyvale · Cupertino · Santa Clara · Los Gatos · Oakland · San Francisco
In 2026, ground-level room additions in the Bay Area typically run $[400–$650] per square foot, and second-story additions $[500–$800]+ per square foot. A 400-square-foot bedroom and bathroom addition commonly totals $[180,000–$280,000]. The biggest cost drivers are whether the addition includes plumbing, ground-level versus second story, and foundation and site conditions.
Construction typically runs 3–6 months depending on size and whether it's a ground-level or second-story addition. Before construction, design, plans, and city permitting usually take 3–6 months in Bay Area cities — so plan on 6–12 months total from first call to final inspection.
A garage conversion is almost always cheaper for the same finished square footage, because the foundation, walls, and roof already exist. Choose an addition when you need more space than the garage provides, want to keep parking, or need the new room adjacent to a specific part of the house. For 200–400 square feet with a sound garage available, the conversion usually wins on cost.
An addition expands your existing home and is best when the new space needs to connect to the house — a primary suite, an extra bedroom, a larger kitchen. An ADU is a separate legal dwelling with its own kitchen and entry, better when you want rental income or full independence for a family member. Many San Jose and East Bay homeowners compare both; we price both paths so you can decide on real numbers rather than guesses.
Always. Additions require architectural and structural plans, building permits, and inspections in every Bay Area city, plus verification that the addition fits your lot's setbacks and coverage limits. Unpermitted additions can't be counted as legal square footage by appraisers and become serious problems during a sale.
Yes — adding permitted square footage triggers a reassessment of the added value in California, though your existing assessed value stays under Proposition 13 protection. Only the new construction is assessed at current value. Your county assessor can estimate the increase, and it's usually far less than homeowners fear.
In most cases yes, but it depends on your existing foundation, framing capacity, and your city's height limits. A structural engineer evaluates whether the foundation and walls can carry the added load — reinforcement is common and budgeted for. Second-story additions cost more per square foot but preserve your entire yard, which on tight Bay Area lots is often decisive.
Usually yes, and more comfortably than during a whole-house remodel — most of the work happens outside the existing envelope until the tie-in. There are typically a few disruptive weeks when the wall is opened and the roof is tied in, plus days when utilities are briefly interrupted. We tell you which weeks those are in advance.
Roofline, pitch, siding profile, stucco texture, window style, and trim details all get matched deliberately — and where an exact match isn't available (discontinued siding, aged stucco color), we advise on solutions that read intentional rather than mismatched. A good addition should be invisible from the curb.
In order of cost per square foot: converting existing space (garage, attic, basement) is cheapest, then a small ground-level bump-out, then a full ground-level addition, then a second story. Skipping plumbing in the new space is the single largest saving available. We'll show you the options with real numbers before you commit to the most expensive one.
Yes — plans, structural drawings, Title 24 compliance, and city submittal are handled as part of the project, and we respond to plan-check comments ourselves. If you already have plans or an architect, we build to their drawings.
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Bedroom and primary suite additions, second-story additions, in-law suites, sunrooms, and small bump-outs across Hayward, Fremont, San Jose, and the Bay Area. Plans, permits, and inspections handled by a licensed general contractor. Free feasibility visit and written itemized quote.