Accessory Dwelling Units are one of the smartest investments you can make in your property. Whether you're creating rental income, housing aging parents, building a home office, or adding a guest suite, an ADU provides flexible, functional space that increases your home's value and utility.
Based in San Mateo, we've helped homeowners throughout Hillsborough, Foster City, Belmont, Burlingame, and San Carlos design and build units that maximize their property's potential. We understand California's ADU laws, the county's specific ordinances, setback requirements, and the streamlined permitting process that makes this type of construction more accessible than ever.
What Makes a Great Accessory Dwelling Unit
Great ADUs feel like complete homes — not just converted garages or backyard sheds. We design each unit with a full kitchen, bathroom, efficient layout, and finishes that match or exceed your main house. The result is a space that's livable, comfortable, and attractive to renters or family members.
We also design for your property's unique characteristics. Setbacks, lot size, existing structures, and access points all influence the layout. We assess your site early in the process to ensure we're building something that fits your property and meets all zoning requirements.
Our Construction Services
- Detached Units: Stand-alone structures built in your backyard with full kitchens, bathrooms, bedrooms, and living areas.
- Garage Conversions: Converting existing garages into livable dwelling units while maintaining or relocating parking.
- Junior ADUs (JADUs): Smaller units created within your existing home, typically 500 sq ft or less.
- Above-Garage Units: Adding a second-story living space above existing or new garages.
- Backyard Studios: Multipurpose spaces that function as home offices, guest suites, or creative studios.
- Two-Story Builds: Maximizing square footage on smaller lots by building vertically.
What to Expect When Building an ADU
California's laws have made it significantly easier to build accessory dwelling units. The county follows state guidelines while adding local requirements. Key regulations include:
- Size Limits: Detached ADUs can be up to 1,200 sq ft (or larger on bigger lots).
- Setbacks: 4-foot minimum rear and side setbacks in most cases.
- Height Limits: 16 feet for single-story units, 18–25 feet for two-story builds depending on zoning.
- Parking: Generally not required within half a mile of transit or in historic districts.
- Owner Occupancy: Required in either the main house or the unit (but not both).
We handle all permitting, architectural drawings, structural engineering, and utility coordination. You won't need to navigate the building department — we manage that entire process.
Typical Project Timeline
Most projects take 6–12 months from design kickoff to completion, depending on complexity:
- Design & Permitting: 2-4 months
- Construction: 4-8 months
- Final Inspections: 1-2 weeks
Garage conversions and smaller units tend toward the shorter end of this range, while detached two-story builds with full utilities can take longer.
Construction Costs
Building an accessory dwelling unit in our area typically costs $250–$450+ per square foot depending on size, complexity, and finishes. A 600-square-foot detached unit generally falls in the $150,000–$270,000 range.
Garage conversions start around $80,000–$150,000 depending on existing conditions and finish level. Larger two-story builds (1,000–1,200 sq ft) can range from $250,000–$500,000+ depending on site conditions and material selections.
These estimates include design, permitting, engineering, foundation, framing, all systems (plumbing, electrical, HVAC), finishes, and landscaping restoration. We provide detailed cost breakdowns during the design phase so you can make informed decisions about scope and finishes.
Return on Investment
Accessory dwelling units on the Peninsula generate strong rental income. A well-designed unit can rent for $2,000–$3,500+ per month depending on size, finishes, and location. That rental income can offset construction financing and generate long-term cash flow.
They also increase property value. Studies show homes with an ADU sell for 20–30% more than comparable properties without one. Even if you don't rent it out, the added functional square footage appeals to future buyers.
Design Considerations
We design every unit to complement your main house while maintaining privacy and independence. Key considerations include:
- Privacy: Strategic window placement, landscaping, and entry orientation to minimize sight lines between main house and ADU.
- Access: Direct street access or side-yard pathways to maintain separation.
- Utilities: Coordinating new water, sewer, electrical, and gas service with existing systems.
- Natural Light: Maximizing windows and skylights to create bright, inviting interiors.
- Storage: Integrated storage solutions to maximize livability in compact spaces.
Why Local Homeowners Choose Lussoro
We're a family-owned design-build firm, which means you work with one team from concept through completion. We don't hand you off to architects, engineers, or subcontractors — we coordinate every aspect of your project and remain accountable throughout.
We've built our reputation on transparency, craftsmanship, and follow-through. We understand this is a significant investment, and we work to deliver a finished product that exceeds expectations and generates real value.
Recent Projects
We recently completed a 750-square-foot detached unit for a homeowner in San Mateo. The project included a full kitchen, bathroom, bedroom, and living area with vaulted ceilings and large windows. It's now rented to a long-term tenant, generating monthly income that helps offset the construction loan.
Another project in Foster City involved converting a two-car garage into a 600-square-foot living space while adding a new carport for vehicle storage. The conversion maintained the home's street-facing character while creating a modern, functional dwelling.
Areas We Serve
We're based in San Mateo and work with homeowners across the Peninsula and Bay Area, including:
- Hillsborough
- Foster City
- Belmont
- San Carlos
- Burlingame
- Redwood City
- Menlo Park
- Palo Alto
Ready to Build Your ADU?
The best way to understand what's possible for your property is to walk the site together. We offer free consultations where we visit your home, assess your lot, discuss your vision, and provide honest feedback about feasibility, timeline, and budget. No obligation, no sales pitch — just a conversation about what could work.
Schedule your free consultation or call us at (925) 399-1238.