ADU guides, page 7
84 guides on what an ADU costs, what the law allows and how to hire well. Every number links to the state law, city page or study it came from.
Cost
1000 sq ft ADU cost in San Diego: price, fees and floor plans
What a 1,000 sq ft ADU costs to build, city and school fees, impact fee rules above 750 sq ft, free plans and what fits.
Updated Oct 27, 2026
Design
1200 square foot ADU: San Diego's largest ADU, plans and cost
San Diego's 1,200 sq ft cap, the County's free 1,200 sq ft plans, 3-bedroom options, cost, fees, the floor area rule above 800 sq ft and one big ADU vs two small ones.
Updated Oct 27, 2026
ADU types
What is a casita? Casita vs ADU vs guest house in California
What a casita is, when it's legally an ADU or guest quarters, San Diego permit rules, cost, design styles and buying a house with a casita.
Updated Oct 27, 2026
Rules
How many ADUs can I build? Counts by lot type in California and San Diego
ADU counts for single-family, duplex and apartment lots, the 2027 change to two detached ADUs, San Diego's density bonus caps and how SB 9 changes the count.
Updated Oct 27, 2026
Design
1 bedroom ADU floor plans: sizes, layouts and costs
What fits from 450 to 800 sq ft, long vs L-shaped vs square layouts, the 500 and 750 sq ft fee lines, builder prices and free plans.
Updated Oct 27, 2026
Design
2 bedroom ADU floor plans: sizes, baths, layouts and costs
Two-bedroom plans from 644 to 1,200 sq ft, one bath vs two, the 1,000 sq ft state rule, two-story options, prices and rents.
Updated Oct 27, 2026
Design
3 bedroom ADU: floor plans, size limits and costs
Whether three bedrooms fit under 1,200 sq ft, plans from 798 sq ft, which cities cap ADUs at 1,000, bedroom egress rules and costs.
Updated Oct 27, 2026
Design
ADU with loft: height rules, ceilings, stairs and cost
Sleeping loft vs mezzanine under the 2025 code, the 16/18/25 ft height limits, ladders and stairs, story counts and fees.
Updated Oct 27, 2026Conversions
Garage conversion ideas: layouts and plans for 1-car, 2-car and 20x20 garages
Studio and one-bedroom layouts by garage size, where the kitchen and bath go, windows, the garage door wall and where to find plans.
Updated Oct 27, 2026
Prefab
Prefab ADU companies in California: published prices compared (2026)
A neutral side-by-side of what Abodu, Samara, Studio Home, Boxabl and others publish, what the prices include, and how to vet a company.
Updated Oct 27, 2026
Prefab
Modular vs manufactured ADU: codes, foundations, financing and cost
HCD modular vs HUD-code manufactured vs panelized vs stick-built: approvals, foundations, Fannie Mae rules, property tax, cost and a decision table.
Updated Oct 27, 2026
Tiny homes
Tiny home vs ADU: cost, financing, resale and rent compared
How a tiny home on wheels and a permitted ADU differ on legal status, up-front cost, loans, appraisal, property tax and rental rules.
Updated Oct 27, 2026