Accessory Dwelling Units (ADUs) and garage conversions are one of the most effective ways to maximize both living space and property value in San Francisco. Whether you’re adding space for family, creating a private guest suite, building a home office, or generating rental income, ADUs offer unmatched flexibility—especially in a city where space is limited and land is expensive.

At Heidi’s House Construction, we specialize in designing and building ADUs that integrate seamlessly with your home’s existing structure while meeting all California and San Francisco zoning, fire-safety, seismic, and building code requirements. From feasibility studies and layout concepts to full construction, plumbing, electrical, and finishes, we deliver ADUs that feel purposeful, comfortable, and built to last.

Why ADUs Make Sense in San Francisco

Compared to traditional additions, ADUs offer faster timelines, lower costs, and fewer zoning constraints. They allow homeowners to create new living areas without expanding the building footprint — ideal for San Francisco’s narrow lots and dense neighborhoods.

• Rental income: Offset mortgage, property tax, or renovation costs.
• Family flexibility: Create space for aging parents, adult children, or long-term guests.
• Work-from-home solutions: Convert unused space into home offices or creative studios.
• Increase property value: ADUs are highly desirable and can significantly raise resale value.
• Better use of existing space: Convert garages, basements, or underutilized lower levels.
• Align with California’s housing goals: ADUs are fully supported by state law—making approvals more predictable.

Because every home is different, the key to a successful ADU is understanding the structure, utilities, and constraints of your building before beginning construction. Our team handles all of this for you.

Types of ADUs We Build

• Garage Conversions: Transforming attached or detached garages into high-quality ADUs.
• Basement ADUs: Converting lower levels under existing living spaces.
• Internal ADUs (Junior ADUs): Carving out units from within existing square footage.
• Attached ADUs: Adding units to the side or rear of homes where feasible.
• ADUs combined with seismic upgrades: Ideal for garage-level soft-story improvements.

Our End-to-End ADU + Garage Conversion Process

1. Feasibility Study & Site Evaluation

We begin with an in-person assessment to understand structure, access, utilities, and zoning factors. We evaluate:

• Interior ceiling heights and headroom compliance
• Foundation type and condition
• Existing plumbing and DWV access
• Electrical panel capacity and routing
• Light, ventilation, and potential egress points
• Fire separation requirements

This allows us to determine what type of ADU is feasible and what upgrades may be required.

2. Concept Design & Budget Development

We work with you to design a comfortable, functional layout that fits your goals. This may include:

• Open-plan studios or 1-bedroom layouts
• Full kitchen or kitchenette options
• Bathroom layout and rough-in planning
• Laundry placement
• Sound insulation strategies
• Private entry and circulation planning

We provide preliminary budgets and help align the scope with your priorities.

3. Engineering, Drawings & Permitting

ADUs generally require a complete permit set and often require structural engineering. We coordinate:

• Architectural plans
• Structural calculations
• Seismic upgrades (cripple walls, shear walls, moment frames)
• Title 24 energy compliance
• Plumbing, mechanical, and electrical drawings
• DBI permit submission and revision handling

Our goal is a smooth, predictable path through San Francisco’s plan review process.

4. Structural Work, Framing & Seismic Improvements

Many ADUs require structural changes—especially garage conversions that need reinforcement to compensate for large openings. Our work may include:

• New foundations or slab upgrades
• New beams, posts, or moment frames
• Cripple wall bracing and shear panels
• Reinforced garage portal frames for soft-story conditions

Combining ADU construction with seismic retrofits can significantly reduce cost and downtime.

5. Rough Plumbing, Electrical & Mechanical

This stage includes:

• Full plumbing for kitchen, bathroom, and laundry
• Drain, waste & vent (DWV) integration with existing systems
• New water heater or shared system tie-ins
• Electrical panel upgrades (if needed)
• New dedicated circuits
• Ventilation fans & ducting
• Mini-split or heat pump heating/cooling systems

We ensure all rough work is accessible for inspection and built cleanly for a long service life.

6. Insulation, Sound Control & Wall Assembly

We install insulation and sound-reducing assemblies to ensure comfort and privacy between the primary home and the ADU. This may include:

• Rockwool or dense-pack insulation
• Resilient channels
• Fire-rated assemblies where required

7. Interior Finishes

We complete the unit with high-quality, durable finishes that work well for long-term tenants, guests, or family:

• Custom cabinetry and kitchen installations
• Durable flooring (LVP, engineered wood, tile)
• Modern lighting
• Tiled showers and backsplashes
• Trim, doors, and closet systems

8. Final Inspection, Testing & Walkthrough

We ensure everything performs correctly—plumbing, electrical, ventilation, fire separation, appliances, and fixtures. Then we walk the unit with you, addressing any final details.

ADU Cost Expectations in San Francisco

Costs depend heavily on structural needs, access, slab condition, finishes, and mechanical systems. Typical ranges:

• Garage Conversion ADUs: $200,000–$450,000+
• Basement ADUs: $200,000–$350,000+
• Internal/Junior ADUs: $80,000–$200,000+
• ADUs combined with seismic retrofits: $350,000–$550,000+

We provide clear, transparent budgets and help phase work when needed.

Common ADU Challenges (and How We Solve Them)

• Low ceiling height: We evaluate options for slab lowering or reconfiguring mechanical runs.
• Limited plumbing access: Our 40+ years of plumbing experience ensures proper DWV and supply layouts.
• Structural changes: We coordinate all engineering and shear wall/portal frame requirements.
• Fire & sound separation: We design compliant assemblies that protect both units.
• Ventilation issues: We integrate mechanical ventilation and passive measures for healthy airflow.

Frequently Asked Questions

Q1: Do ADUs require permits in San Francisco?

A1: Yes. All ADUs require permits and, in most cases, full architectural and structural plans. We manage the entire permitting process.

Q2: How long does an ADU take to build?

A2: Timeline varies by type, but typical ranges are 6–12 months for design, permitting, and construction combined.

Q3: Can I live in my home during construction?

A3: In most cases, yes. We plan work to minimize disruption and maintain access to your main living areas.

Q4: Can an ADU have separate utilities?

A4: Yes. We can install separate water heaters, subpanels, and even sub-metering if desired.

Q5: Does converting my garage require seismic upgrades?

A5: Often yes. Garage openings create soft-story conditions, so seismic improvements are commonly required.

Q6: Can I use my ADU as a rental?

A6: Yes — ADUs are permitted rentals under California law. We can build with long-term durability in mind.

Next Steps

If you're considering an ADU or garage conversion in San Francisco, we’d be happy to evaluate your property, discuss layout options, and map out a clear plan. Contact us to schedule a consultation and explore the possibilities within your existing footprint.