ADU accessory dwelling unit
What is an ADU and can I build one on my property?
Projekt-Plan
Why: Choosing the right type (Detached, Attached, Conversion, or Junior ADU) dictates your budget and legal constraints.
How:
- Evaluate a Detached ADU for maximum privacy or a JADU (under 500 sq ft) for lower fees.
- Decide if the goal is rental income, multi-generational living, or a home office.
- Read 'Backdoor Revolution' by Kol Peterson for the definitive guide on ADU development strategies.
Done when: You have selected one specific ADU type for your project.
Why: Zoning determines the 'legal' possibility of your build before you spend money on designs.
How:
- Check for State Preemption (e.g., CA, WA, OR) which often overrides local bans on ADUs.
- Confirm 4-foot side and rear setbacks and maximum height limits (usually 16-25 ft).
- Use your city's online GIS portal to check for easements or protected zones on your lot.
Done when: You have a written confirmation or map showing your buildable area.
Why: ADU projects take 6–18 months; planning backwards ensures you meet critical deadlines like school starts or lease endings.
How:
- Set a Target Move-In Date.
- Subtract 6 months for construction and 4 months for permitting/design.
- Mark the Permit Submission as your first major 'hard' deadline.
Done when: A calendar exists with a clear start date and move-in milestone.
Why: Underestimating 'Soft Costs' (permits, design) is the #1 reason ADU projects stall.
How:
- Allocate 15-25% for Soft Costs ($15k–$30k for architecture and permits).
- Estimate Hard Costs at $300–$500 per sq ft for mid-range finishes.
- Include a 20% contingency fund for utility upgrades (e.g., new electrical panels).
Done when: You have a spreadsheet with a total estimated cost and a 20% buffer.
Why: Most homeowners use home equity; securing this early prevents construction delays.
How:
- Apply for a HELOC (Home Equity Line of Credit) for flexibility.
- Explore Construction-to-Permanent loans if you have low equity.
- Check for local ADU Grant Programs (some cities offer up to $40k for low-income rentals).
Done when: You have a pre-approval letter or funds in a dedicated account.
Why: ADUs require specialized knowledge of small-space efficiency and specific ADU building codes.
How:
- Interview 3 pros who have completed at least 5 ADUs in your specific city.
- Ask for Pre-approved Plans to save $5k–$10k in design fees and weeks in permitting.
- Verify licenses via your state's Contractor State License Board (CSLB).
Done when: Signed contracts with an architect and/or general contractor.
Why: Designing for accessibility (curbless showers, wide doors) increases long-term value and utility.
How:
- Ensure 36-inch wide doorways for wheelchair access.
- Plan a Kitchenette with induction cooktops to avoid gas line costs.
- Use 'ADUs: The Perfect Housing Solution' by Sheri Koones for small-space design inspiration.
Done when: Completed architectural set ready for city submission.
Why: This starts the official 'shot clock' (usually 60 days) for city approval.
How:
- Submit Site Plans, MEP (Mechanical/Electrical/Plumbing), and Title 24 energy reports.
- Confirm Impact Fee Exemptions (in CA, ADUs <750 sq ft are exempt from most impact fees).
- Track the application weekly via the city's permit portal.
Done when: A permit application number and receipt for paid fees.
Why: A solid foundation prevents future structural settling and water intrusion.
How:
- Clear vegetation and trench for utilities (sewer/water/electric) from the main house.
- Install Formwork and Rebar according to structural engineering specs.
- Schedule a Pre-pour Inspection with the city building official.
Done when: Cured concrete foundation with utility stubs in place.
Why: Getting the structure 'dried-in' protects interior materials from weather damage.
How:
- Erect Wall Studs and roof rafters.
- Install Windows and Exterior Doors with proper flashing.
- Apply Roofing Shingles or metal panels immediately after framing.
Done when: The structure is fully enclosed and weather-tight.
Why: Mechanical, Electrical, and Plumbing (MEP) must be inspected before walls are closed.
How:
- Install PEX plumbing lines and electrical wiring.
- Set up a Mini-split HVAC system (most efficient for ADUs).
- Schedule the Rough-in Inspection before installing insulation.
Done when: Passed city inspection for plumbing, electrical, and mechanical.
Why: Bathrooms are the most complex interior spaces; finishing them first allows for early utility testing.
How:
- Install Waterproof Backer Board and tile the shower.
- Set the Low-flow Toilet and vanity.
- Install a High-CFM Exhaust Fan to prevent mold in small ADU spaces.
Done when: A fully functional, tiled, and plumbed bathroom.
Why: The kitchen is the heart of the ADU and requires precise electrical/plumbing alignment.
How:
- Use Space-saving Appliances (24-inch fridge, 18-inch dishwasher).
- Install Quartz Countertops for durability in rental scenarios.
- Mount Under-cabinet Lighting to make the small space feel larger.
Done when: Kitchen cabinets, counters, and appliances are installed and powered.
Why: These areas require the final aesthetic touches like flooring and paint.
How:
- Lay LVP (Luxury Vinyl Plank) Flooring for maximum water and scratch resistance.
- Paint walls with Light, Neutral Colors (e.g., Off-white) to maximize light.
- Install Built-in Storage or Murphy beds to optimize the small footprint.
Done when: Flooring, paint, and trim are complete in all remaining areas.
Why: You cannot legally occupy the ADU without a final sign-off from the building department.
How:
- Ensure all Smoke and Carbon Monoxide Detectors are installed and tested.
- Verify that Egress Windows in the bedroom meet code requirements.
- Walk the site with the inspector to address any minor 'punch list' items.
Done when: A signed-off permit card or Certificate of Occupancy.
Why: Finalizing the unit with furniture and utilities completes the project.
How:
- Set up Separate Trash/Recycling bins for the ADU.
- Install a Smart Lock for easy keyless entry (ideal for rentals or guests).
- Create a Home Manual explaining the mini-split, water shut-off, and Wi-Fi.
Done when: The unit is furnished, clean, and ready for the first occupant.