Need more living space? A conventional addition and an accessory dwelling unit (ADU) may solve different problems. An ADU often contains independent living facilities; a house addition usually expands the primary residence.
ADUs and additions are not interchangeable
A bedroom extension or family-room addition is integrated into the main home. A detached ADU is a separate small dwelling, while attached ADUs and conversions can share walls, utilities or existing structure with the main house. Local laws determine what qualifies as an ADU, including kitchen, bathroom, separate entrance and occupancy requirements.
If you primarily need a larger shared kitchen or a playroom, conventional expansion may be a better fit. If you want independent living space for an aging parent, adult child or long-term tenant, an ADU might provide more flexibility, if your property and jurisdiction allow it.
Budget: building new versus reusing structure
Angi’s 2026 ADU guide describes a broad typical range around $150–$300 per sq ft, with higher numbers for complex builds and lower entry costs for some conversions. A fully detached ADU normally requires substantial infrastructure: foundation, framing, roof, utility connections, kitchen, bath and heating/cooling.
Conversions may avoid some new structural work, but savings depend on existing slab height, insulation, egress, plumbing routes and code compliance. A garage that looks finished from the street may still need expensive work to meet habitation rules.
| Question | Home addition | ADU |
|---|---|---|
| Independent living | Usually no | Often yes |
| Full kitchen required | Not necessarily | Often yes |
| Rental possibility | Depends on local rules | Depends on local rules |
| Separate utilities | Usually connected | May need upgrades |
| Zoning constraints | Height, coverage, setbacks | ADU standards and local rules |
Why rental projections need caution
A backyard rental unit can look appealing when someone multiplies local advertised rent by 12. Gross rent does not equal net cash flow. Vacancy, property tax effects, insurance, ongoing repairs, management and periodic replacements all reduce the usable income.
Our ADU calculator asks you to enter local rent, vacancy and operating expenses separately. It displays a simple payback illustration, not a promise of return or a substitute for detailed real-estate underwriting. If an ADU is for a family member, assess its lifestyle value separately from financial income.
Check feasibility before paying for full design
Start with a property survey, zoning map, setback requirements, lot coverage and available utility connections. Ask the local planning department about height limits, parking, fire access, owner-occupancy and long-term rental rules. Regulations change, so generalized internet statements about what a state allows can be misleading for a specific property.
For a conventional addition, investigate structural tie-ins, existing foundation, site drainage and whether the floor plan still works after expansion.
A practical decision framework
- Write down the primary use: shared space, independent family living, rental income or home office.
- Confirm property constraints before assuming an ADU or addition is feasible.
- Calculate two all-in scenarios with permits, site conditions and contingency.
- Evaluate comfort, privacy, ongoing operating costs and any actual local rental restrictions.
- Obtain comparable designs and written quotes from local qualified professionals.
Sources
- Angi (2026), How Much Does a Home Addition Cost?
- Angi (2026), How Much Does an ADU Cost to Build?
- Angi (2026), How Much Does It Cost to Add a Second Story?
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