Every cost,
in plain view.

Estimated total

Planning ranges as of October 2026, not quotes. Your cohort proposal turns the fixed parts into firm numbers, and your site review narrows the rest.

1. 1Design and coordinationFixed

   One flat ADUStack fee from first site visit to move-in.

   	749 sq ft home	1,199 sq ft home
   Plan adaptation to your lot and finish choices	$5,000–$7,000	$6,000–$8,500
   Structural engineering and Title 24 energy report	$3,000–$5,000	$3,500–$6,000
   Permit coordination with your city	$2,000–$3,000	$2,500–$3,500
   Project coordination and materials sourcing	$2,000–$3,000	$3,000–$4,000
   Subtotal	$12,000–$18,000	$15,000–$22,000

2. 2City feesDepends on your site

   Paid to your city and school district. The 749 sq ft plan avoids city impact fees entirely.

   	749 sq ft home	1,199 sq ft home
   Building permit and plan check	$3,000–$12,000	$4,000–$15,000
   School district fees¹	$4,000	$6,500
   City impact fees²	$0	$5,000–$20,000
   Subtotal	$7,000–$16,000	$15,500–$41,500

   ¹ Most districts charge up to $5.38 per square foot of home size (the 2026 state cap) on ADUs over 500 sq ft. ² California bars impact fees on ADUs of 750 sq ft or less. Above that, cities may charge fees scaled to the ADU’s size.

3. 3Utilities and connection feesDepends on your site

   Getting water, sewer, and power from your main home to the ADU. Distance from the house and your existing electrical service drive most of this.

   	749 sq ft home	1,199 sq ft home
   Water and sewer lines (trenching and pipe)	$6,000–$15,000	$7,000–$16,000
   Electrical feed and subpanel	$4,000–$8,000	$5,000–$9,000
   PG&E service upgrade (only if your home has under 200 amps)	$0–$8,000	$0–$10,000
   Water and sewer connection or capacity fees (only if a separate meter is required)	$0–$4,000	$0–$5,000
   Subtotal	$10,000–$35,000	$12,000–$40,000

4. 4FoundationDepends on your site

   Slab-on-grade, the simplest and most cost-effective foundation for a single-story ADU on a flat lot. Soil conditions, slope, and equipment access can change it.

   	749 sq ft home	1,199 sq ft home
   Soils report and foundation engineering	$2,000–$4,000	$2,000–$4,000
   Slab: excavation, forms, rebar, concrete$18–$30 per sq ft	$13,500–$22,500	$21,500–$36,000
   Subtotal	$15,500–$26,500	$23,500–$40,000

5. 5The home itself (vertical construction)Fixed

   Everything from the top of the foundation up. Fixed per plan once your cohort’s contractor bid is in.

   	749 sq ft home	1,199 sq ft home
   Core materialsWhat’s inside the walls once it’s finished: framing or prefab structure, sheathing, roof structure and underlayment, insulation, rough plumbing and wiring, heating and cooling equipment and ducts, drywall.$70–$95 per sq ft	$52,500–$71,000	$84,000–$114,000
   Finish materialsWhat you see and touch: windows and doors, siding and roofing, flooring, cabinets and countertops, tile, plumbing fixtures, lighting, appliances, paint.$55–$85 per sq ft	$41,000–$63,500	$66,000–$102,000
   LaborThe crew that builds it: framing and assembly, plumbing, electrical and HVAC trades, drywall, finish carpentry, flooring, painting, cleanup, and on-site supervision.$120–$160 per sq ft	$90,000–$120,000	$144,000–$192,000
   Subtotal	$183,500–$254,500	$294,000–$407,500