What's Included in an ADU Budget?
A complete ADU budget is more than framing and finishes. Ask contractors to separate allowances and assumptions for:
- Design, engineering, survey, and permit drawings
- General contractor labor and subcontractor coordination
- Foundation, framing, roofing, windows, siding, insulation, and finishes
- Building, zoning, plumbing, electrical, mechanical, and inspection fees
- Utilities, trenching, septic or sewer work, water tie-ins, and service upgrades
Detached ADU vs Conversion
Conversions can be more affordable when the existing garage, basement, or finished space already meets structural, ceiling height, egress, moisture, and utility requirements. Detached ADUs provide more privacy and flexibility but usually require a foundation, new utility connections, exterior envelope, and more site work.
Three Cost Drivers to Ask About
Site and access - Tight lots, slopes, ledge, drainage, tree removal, and limited equipment access can add significant cost.
Utilities - Electrical service, HVAC, water, sewer or septic capacity, trenching, and meter configuration can change the budget quickly.
Permits and scope clarity - Zoning review, revisions, engineering, inspections, allowances, and exclusions should be clear before work starts.