Typical cost range
$80,000 – $250,000+
Typical timeline
3 – 6 months
Accessory Dwelling Units (ADUs) and home additions add livable space and property value. ADUs — whether detached, attached, or garage conversions — create rental income or multigenerational living space, while additions expand your home's footprint for growing needs.
Types of ADUs and additions
Detached ADUs are standalone structures in the backyard. Attached ADUs share a wall with the main house. Garage conversions repurpose existing structures. Home additions (second story, bump-out, great room) expand the primary residence. Each has different permitting, cost, and timeline implications.
Permits and zoning
ADUs are subject to state and local zoning rules covering setbacks, height, parking, and owner-occupancy. California has streamlined ADU approval, but you still need full plans, structural engineering, and utility connections. A contractor experienced in ADUs navigates this for you.
Utilities and systems
Most ADUs require a separate or shared electrical panel, water heater, and HVAC. Sewer and water connections often trigger upgrades. Planning these systems early — before framing — prevents costly rework and change orders.
Smart tips before you start
- Check local ADU ordinances early — rules on size, height, and parking vary by city.
- Budget for utility upgrades (panel, sewer lateral) which are often underestimated.
- Pre-approved ADU plans can save months of design and permitting time.
- Design for energy efficiency from day one; it pays off over the unit's lifetime.
Every project is unique. The ranges above are typical — your actual cost and timeline depend on your home, materials, and scope. Get quotes from licensed contractors to compare real numbers.