Room additions and Accessory Dwelling Units (ADUs) expand living space on your property. A room addition extends the existing home's footprint, while an ADU is a self-contained dwelling unit with its own kitchen and bathroom — also known as a granny flat, in-law suite, or guest house.
10 steps across 1 sections
1. Steps Guide
- Check zoning and local regulations — Contact your city planning department to determine what is allowed on your property. Key factors: lot size requirements, setback restrictions, height limits, ma...
- Define the project scope — Room addition: extending the existing home (bedroom, family room, sunroom). ADU types: attached (added to existing home), detached (standalone structure), garage conversi...
- Set a realistic budget — Room additions: $80-$300/sq ft ($40,000-$150,000 typical). ADU new construction: $150-$400/sq ft ($100,000-$300,000). Garage conversion: $25,000-$100,000. Add 15-20% contin...
- Hire an architect or designer — Professional plans ($8,000-$15,000 for ADUs) are required for permits and ensure code compliance. Some jurisdictions offer pre-approved ADU plans that reduce design ...
- Engage a structural engineer — Foundations, load-bearing connections, and seismic requirements need engineering analysis. This is mandatory for permit approval and costs $2,000-$5,000.
- Obtain permits — Building permits ($5,000-$10,000 for ADUs), plus separate permits for electrical, plumbing, and mechanical work. Impact fees and school fees may apply. Permit processing takes 4-12...
- Hire a licensed general contractor — Get 3+ bids from contractors experienced with additions or ADUs. Verify licensing, insurance, and references. Sign a detailed contract with scope, timeline, and...
- Plan utility connections — Water, sewer, electrical, gas, and internet must be extended to the new space. ADUs may require separate utility meters. Utility connection fees can be significant ($5,00...
- Manage construction — Typical timeline: foundation (1-2 weeks), framing (2-3 weeks), rough-in MEP (2-3 weeks), insulation and drywall (1-2 weeks), finishes (2-4 weeks), final inspections (1-2 weeks...
- Final inspection and occupancy — Pass all final inspections, obtain a Certificate of Occupancy, update your homeowner's insurance, and file an updated property assessment if required.
Common Mistakes
- Not checking zoning first
- Underestimating utility costs
- Ignoring impact on existing home
- Not considering rental regulations
- Choosing the cheapest option
Pro Tips
- Look for pre-approved ADU plans
- Explore ADU financing options
- Check state incentive programs
- Consider prefabricated ADUs
- Design for rental income