The statutory switch
State law guarantees a studio or one-bedroom ADU of at least 850 sq ft, and a two-plus-bedroom ADU of at least 1,000 sq ft — local caps can't cut below those floors. Separately, development impact fees are exempt at 750 sq ft or less, and school fees are fully exempt at 500 sq ft or less (see our fee guide and checker).
Notice the tension: the two-bedroom guarantee starts at 1,000 sq ft — above the 750 sq ft fee-exemption line. A compact one-bedroom at 749 sq ft can dodge impact fees entirely; a two-bedroom at its guaranteed size can't. That doesn't make either choice wrong — it makes the fee line part of the bedroom decision, which most homeowners never hear until the fee estimate arrives.
Side by side
| Factor | Studio / 1-bedroom | 2+ bedrooms |
|---|---|---|
| Guaranteed size floor | 850 sq ft | 1,000 sq ft |
| Impact-fee exemption (≤750 sq ft) | Achievable — many 1BR plans fit under 750 | Usually exceeded at functional 2BR sizes |
| Construction cost | Lower — less area, one bath typically | Higher — more area, often a second bath; scale with our cost ranges |
| Best-fit uses | Single renter or couple, office/flex, aging parent | Small families, roommate rentals, multigenerational households |
| Rent potential | Market-dependent — bedroom count matters, but so do neighborhood and quality; we don't publish per-bedroom rent figures because honest ones are hyperlocal | Same caveat — model both with your own local comps in the ROI calculator |
| Local wrinkles | Fontana allows the larger of 50% of the main house or the 850/1,000 floors — on a big house, two bedrooms may cost nothing in allowance. Burbank's materials require 2+ bedrooms for any ADU over 850 sq ft. City rules shape this choice — check yours in the Rules Explorer. | |
How to decide in four questions
- Who's actually living there in year one? Design for the real occupant, not the hypothetical maximum.
- Does 749 sq ft solve it? If a compact 1BR meets the need, the fee exemption is a real, statutory saving — run your size through the fee checker.
- Does the lot even allow the bigger unit comfortably? The size calculator plus our small-lot guide answer the envelope question.
- Run both through your budget — the ADU plan builder prices both sizes against the published ranges in two minutes each.
Frequently asked questions
Not automatically. Rent scales with bedrooms, but so does build cost — and the fee exemption at 750 sq ft can swing the total-cost math toward a compact one-bedroom. Model both with local comps; our rental income guide covers the honest framework.
Cities can apply objective standards, but they can't cap a 2+ bedroom ADU below 1,000 sq ft or a studio/1BR below 850. Some cities add structure — Burbank's materials tie 850+ sq ft units to a 2-bedroom minimum — so check your city's layer in our guides.
Only indirectly — assessment follows the ADU's value (roughly its construction cost), and a bigger unit costs more. Our tax estimator shows the blended-assessment math at any budget.