Costs
2025 cost ranges, calculators, and real-world budgets by ADU type.
Open CostsPlan your ADU with confidence in 2025
Clear guidance on ADU costs in 2025, local regulations, finding trusted builders, and financing options—plus city-by-city playbooks to get you from idea to move-in.
TL;DR — Most homeowners start by sizing their budget, then confirm local rules, gather builder quotes, and choose a financing path. We’ve organized everything into that exact flow.
Step 1 of 4 • Costs → Regulations → Builders → Financing
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Key ADU facts for 2025
- Typical turnkey cost: $150k–$350k by ADU type and site {{verify locally}}.
- Common detached size: 400–800 sq ft (local caps vary) {{verify locally}}.
- Illustrative payback via rent: ~8–12 years (market-dependent) {{verify locally}}.
- Financing paths: HELOC, cash-out refi, construction loan, FHA 203k.
- Permit timeline target: ~6–10 weeks for administrative review when plans are complete {{verify locally}}.
How to plan your ADU: 4 key steps
Regulations
State and city rules—size, setbacks, parking, owner-occ, and fees.
Open RegulationsBuilders
Prefab vs. custom, directories, and a simple RFQ to compare quotes.
Open BuildersFinancing
HELOC, cash-out, construction loans, FHA 203k—compare payments.
Open FinancingFeatured prefab resource
Considering modular or panelized ADUs? See trusted prefab options and get matched via our RFQ.
~6–10 weeks
1–3 days
Case studies & payback snapshots
~8–12 yrs
$150k–$350k
10–15%
Frequently asked
What ADU size fits a typical backyard?
Many lots can fit a 400–800 sf detached ADU, but setbacks, height, lot coverage, and utilities control the final envelope. Check your city’s setbacks and max size on the Regulations page.
Is a garage conversion cheaper than a new detached ADU?
Often, yes—existing foundations and utilities can lower costs. Scope still matters (seismic, slab, insulation, egress). Compare your options on Costs.
Prefab or custom: which is faster?
Prefab can compress the on-site timeline; custom can fit tricky lots and HOA rules. See pros/cons and a builder directory on Builders.
How do people finance an ADU?
Common paths are HELOC, cash-out refinance, construction loans, or FHA 203k. Compare speed, paperwork, and payments on Financing.
Will an ADU increase property taxes?
Yes, the improvement value gets assessed separately in many jurisdictions. We link to official resources and suggest verifying with your county assessor. {{verify locally}}
Can I rent out my ADU short-term?
Short-term rental rules vary widely and often differ from long-term ADU allowances. Always confirm with your city’s municipal code or planning portal. {{verify locally}}