ADU income on a DSCR file: what counts, and what does not

Why ADUs matter more in California than anywhere else

State law has progressively stripped away the local barriers to building accessory units: parking requirements, owner-occupancy requirements in many cases, and discretionary review. Cities have responded with pre-approved plans and fee reductions. The result is a large and growing stock of second units on single-family lots, from converted garages in Long Beach to new two-story units behind a house in Sacramento.

For an investor, the appeal is straightforward: a property that produced one rent now produces two, and the second rent often comes with a much lower incremental cost than buying another parcel. In a state where entry prices are the binding constraint, that is the cheapest way to add coverage.

The four things a lender will verify

Permitted. The unit has to be legal. A finished garage with a kitchenette and no permit is a liability, not an income stream, and a lender will not count it. An older unpermitted unit may have a legalization path under state or local rules — confirm it with the city building department, and do it before a refinance rather than after.

Rentable. Local rules and HOA covenants can restrict short-term or even long-term rental of an accessory unit. If the unit cannot legally be rented, its income does not exist for underwriting purposes.

Documented. A signed lease is the strongest evidence. Absent a lease, the appraiser’s market rent opinion can support the income, but a lender weighs that more cautiously — particularly where the unit is new and has no rental history.

Insurable. A second dwelling changes replacement cost, and some carriers treat an ADU as a separate structure requiring its own coverage or a rider. The premium belongs in the coverage denominator, and a policy that does not acknowledge the unit is a problem at closing.

• Permit history and certificate of occupancy for the unit
• The lease, with dates and rent, if it is currently occupied
• Any local ordinance or HOA restriction on renting the unit
• An insurance quote that explicitly covers the second dwelling

How the appraisal treats a second unit

An appraiser valuing a house with a rented ADU is not simply adding the rent to the house value. The unit can shift the property into a different comparable set, and the income approach may be weighted more heavily than it would be for a plain single-family rental. That is usually favorable, but it also means the appraisal depends on the unit being permitted and marketable.

Where the ADU is unpermitted, the appraiser may still value the space as storage or bonus area while explicitly declining to credit rental income. That is the worst outcome for a DSCR file: higher value, no coverage support.

Timing the refinance around a new unit

If you are building the ADU now, finish it, get it signed off, lease it, and then refinance. A file assembled mid-construction usually produces a lender who wants the work complete before closing — which costs time and can cost a rate lock. Sequence it deliberately: permits, construction, final inspection, lease, then the DSCR refinance sized on both rents.