ADU Construction San Mateo | Custom Accessory Dwelling Units
Complete ADU construction in San Mateo with permits handled, custom designs, and quality building that creates rental income and solves housing needs.
San Mateo ADU Construction That Actually Adds Value
Need extra space or rental income from your San Mateo property? We build custom accessory dwelling units that work for your specific situation – whether that’s housing for aging parents, rental income to help with mortgage payments, or a home office separate from your main house.
Our team handles everything from initial feasibility studies through final occupancy permits. No bouncing between architects, contractors, and permit runners. One licensed team manages your entire ADU project with clear timelines and upfront pricing.
Real Results: Most ADU projects completed in 4-6 months with permits handled and city inspections coordinated throughout construction.
Licensed Contractor #1104331 | Serving South San Francisco Since 2023
Complete ADU Construction Services
Your ADU construction includes site analysis, custom design, permit coordination, and skilled building so you get a unit that works perfectly for your intended use.
San Mateo ADU construction starts with understanding how you plan to use the space. Rental units need different features than in-law suites or home offices. We design each ADU around your specific goals, whether that’s maximizing rental income or creating comfortable multigenerational living.
Our construction process covers foundation work, framing, electrical and plumbing installation, insulation, drywall, flooring, kitchen and bathroom construction, and all finish work. We handle San Mateo building permits and coordinate inspections at each phase.
What’s included in every ADU project:
- Site feasibility study and design consultation
- All permits and city inspection coordination
- Foundation work and utility connections
- Complete electrical system with separate meter option
- Full plumbing installation for kitchen and bathroom
- Insulation, drywall, and interior finish work
- Kitchen construction with appliances and storage
- Bathroom build-out with quality fixtures
- Final cleanup and occupancy permit
We often coordinate ADU construction with whole home renovations when families are updating both their main house and adding rental space simultaneously.
ADU Layouts Built Around How You'll Use the Space
Every ADU design starts with understanding your goals – rental income, family housing, or flexible space – then creates layouts that work efficiently within your lot constraints.
Detached ADU construction works best for rental income since tenants get complete privacy from your main house. We design these units up to 1,200 square feet with full kitchens, bathrooms, living areas, and separate entrances. Perfect for long-term tenants or short-term rentals in San Mateo’s strong housing market.
Attached ADU additions connect to your main house but maintain separate living quarters. These work well for aging parents who want independence while staying close to family, or adult children who need their own space but shared family connection.
Popular ADU configurations we build:
- Studio layouts with efficient kitchen and bathroom placement
- One-bedroom units with separate living and sleeping areas
- Two-bedroom designs for families or shared rental arrangements
- Home office ADUs with bathroom and kitchenette
- In-law suites with accessibility features and private entrances
- Flexible spaces that work as guest quarters or rental units
Our designs work within San Mateo’s setback requirements and architectural guidelines, ensuring your ADU complements your existing home and neighborhood character.
Garage Conversion and Basement ADU
Garage conversions and basement ADUs use space you already have, often costing less and completing faster than new construction while still creating valuable living areas.
Garage conversion ADU projects work well when you don’t need car storage or have alternative parking. We handle structural modifications to create proper ceiling heights, install windows for natural light, and add insulation for year-round comfort. Most garage conversions include bathroom additions and kitchen installation.
Basement ADU conversions require addressing ceiling height, egress windows, and moisture control. We install proper drainage, ventilation systems, and waterproofing to create comfortable below-grade living spaces that meet safety requirements.
Conversion services we provide:
- Structural analysis and modification for safe living spaces
- Window installation for natural light and emergency egress
- Moisture control and waterproofing systems
- Electrical upgrades including separate circuits and outlets
- Plumbing installation for new bathrooms and kitchens
- Insulation and climate control for year-round comfort
- Flooring installation over concrete or existing surfaces
These projects often coordinate well with bathroom renovations in your main house when we’re already running plumbing lines and electrical circuits.
JADU and Small Space ADU Solutions
Junior ADUs and compact designs provide affordable ways to add rental income or family housing without the complexity and cost of full-sized units.
Junior ADU (JADU) construction creates units up to 500 square feet within your existing home structure. These work well for converting large bedrooms, bonus rooms, or garage spaces into independent living quarters with kitchenettes and shared or separate bathroom access.
Small ADU designs maximize every square foot through clever storage solutions, multi-purpose furniture areas, and efficient kitchen and bathroom layouts. We specialize in creating comfortable living spaces that don’t feel cramped despite compact footprints.
Small space ADU features we design:
- Murphy beds and fold-down surfaces for flexible room use
- Galley kitchens with full appliances in minimal space
- Combination washer-dryer units and built-in storage
- Loft sleeping areas with living space below
- Outdoor access and patio areas that extend living space
- Smart home features for efficient lighting and climate control
These efficient designs often work well with kitchen remodeling projects when you’re updating both main house and ADU kitchens with coordinated appliances and finishes.
Navigating City Requirements Without the Headaches
San Mateo’s ADU regulations have simplified in recent years, but proper permit handling still requires knowing current codes, setback rules, and inspection schedules.
San Mateo allows ADU construction on most single-family properties with streamlined approval processes. We handle feasibility studies to determine what size and type of ADU works within your lot’s constraints and zoning requirements.
Current San Mateo ADU regulations allow units up to 1,200 square feet for detached construction, with height limits typically at 16 feet. Setback requirements are 4 feet from rear and side property lines in most cases. No additional parking requirements exist within half-mile of transit stops.
Permit services we handle:
- Site surveys and zoning compliance analysis
- Architectural drawings and engineering plans
- Building permit applications and submissions
- Planning department coordination and approvals
- Inspection scheduling throughout construction phases
- Certificate of occupancy applications and approvals
We stay current with changing ADU regulations to ensure your project meets all requirements and qualifies for streamlined approval processes that reduce permit timeline to 60-90 days maximum.
ADU Investment and Rental Income Planning
San Mateo’s strong rental market makes ADUs attractive investments, but success depends on building the right unit for your target tenants and local rental rates.
San Mateo ADU rental rates typically range from $2,000-$4,000 monthly depending on size, features, and location within the city. Well-designed units in desirable neighborhoods often rent quickly and maintain high occupancy rates.
Investment planning considers construction costs against potential rental income, property value increase, and tax implications. We help you understand realistic timelines for return on investment and design features that attract quality long-term tenants.
Features that increase rental desirability:
- Separate parking spaces and private entrances
- In-unit laundry and modern appliances
- Outdoor space like patios or small yards
- Energy-efficient features that reduce tenant utility costs
- Sound insulation between ADU and main house
- Quality finishes that photograph well for rental listings
Many homeowners combine ADU construction with exterior renovations like landscaping, fencing, and outdoor lighting that enhance both main house and rental unit appeal.
Ready to Start Your San Mateo ADU Project?
Get a detailed feasibility study and cost estimate for your ADU construction. We'll assess your property, explain permit requirements, and show you design options that work within your budget and goals
Get Started with Your ADU Project
Schedule a consultation to discuss your accessory dwelling unit options. We’ll assess your property, explain permit requirements, and provide detailed project estimates.
What we cover during consultation:
- Property feasibility assessment
- ADU design options for your lot
- Permit requirements and timeline
- Construction cost estimates
- Zoning compliance review
Romy Construction Inc serves the San Mateo County and surrounding Bay Area communities. Licensed general contractor specializing in ADU construction and home remodeling.
Phone: (415) 813-7931
Email: info@romyconstructioninc.com
Licensed Contractor #1104331
ADU Questions San Mateo Property Owners Ask
The real questions people want answered before starting their ADU project.
Most single-family homes qualify if you have adequate yard space for setbacks and utilities. Your lot needs room for a 4-foot setback from property lines and access for construction. We do free feasibility studies to determine what works on your specific property.
Detached ADUs typically run $150K-$300K depending on size and finishes. Garage conversions cost $80K-$150K. JADUs start around $50K-$100K. Final cost depends on site conditions, permit requirements, and features you choose.
Yes, we manage the entire permit process from initial applications through final occupancy certificates. San Mateo has streamlined ADU approvals, but proper paperwork and inspections still require someone who knows the system.
You can rent your ADU as long as you live in either the main house or the ADU. San Mateo doesn't require owner occupancy waiting periods like some cities. We help coordinate final inspections so you can start renting as soon as construction completes.
San Mateo doesn't require additional parking for ADUs within half-mile of transit stops, which covers most of the city. If parking is required, we help design solutions that work within your lot constraints.
Garage conversions: 3-4 months. New detached ADUs: 5-6 months. JADUs: 2-3 months. Weather, permit approval speed, and change orders can affect timelines. We provide realistic schedules during initial planning.
Locally Trusted Since 2023 – Specializing in South San Francisco, San Francisco County, Marin County & San Mateo County
Our Bay Area clients consistently praise how we blend regional expertise with quality craftsmanship to deliver exceptional results. Having served local homeowners since 2023, we’ve mastered the unique challenges of home renovations—from coastal humidity considerations to navigating strict permitting processes—ensuring every project meets both your vision and local standards.
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