Homes with ADU · Buying guide
An accessory dwelling unit changes everything about how you evaluate a property: how to inspect it, how to finance it, what to verify legally, and how to model the after-move-in economics. This guide walks through each step, from pre-offer due diligence to what to nail down before signing the closing documents.
A legal, permitted ADU adds three things to a property: separate living space (suitable for guests, family, or tenants), rental income capacity (typically $1,500–$3,500/month depending on market and unit size), and a defensible 15–40% premium over a comparable single-unit home. An unpermitted or improperly-built ADU adds none of those reliably. Often it adds legal exposure — cities can require post-purchase remediation, demolition, or owner-occupancy compliance that an unsuspecting buyer didn't sign up for.
The first question for any ADU-equipped home is: is this a real ADU? The pre-offer checklist below answers that question before you spend time on the inspection.
Run this list before submitting an offer. Each item takes under an hour and can save you weeks of post-offer surprises. If any item turns up something concerning, factor it into your offer price or walk away — it's much cheaper to walk away pre-offer than to discover the ADU is unpermitted three days before closing.
A standard home inspection covers the main house. For the ADU, explicitly ask your inspector to scope it as a separate dwelling and produce a separate findings list. Expect $200–$400 in additional inspection cost. The items below are ADU-specific and routinely missed when an inspector treats the ADU as bonus space.
Lenders treat ADU-equipped homes differently than single-unit homes, and the differences matter for both your debt-to-income calculation and the price the appraiser supports.
ADU rental income: Fannie Mae allows up to 75% of either documented historical rent or projected market rent (from a Form 1007 rent schedule) to count toward DTI on conventional loans. Freddie Mac is similar. FHA allows ADU income only if the property is owner-occupied and the ADU is legally permitted. VA loans have varied policies by lender.
Appraisal comp issues: Appraisers find ADU comps by looking for similar properties that have recently sold. In markets with thin ADU stock (most of TX, FL, CO), the appraiser may not find good comps and will value the ADU as “additional improved square footage” rather than as a separate income unit. This can leave a $30K–$80K gap between your contract price and the appraised value — meaning more cash to close.
Insurance:Standard homeowner policies cover ADUs that are part of the same parcel as the main home. If you plan to rent the ADU long-term or short-term, you'll need a landlord rider or a separate rental dwelling policy, typically adding $300–$800/year.
These items should be confirmed during your contingency period — not afterward. Most are straightforward calls or portal lookups; a few require an attorney review.
Do I need a separate inspection for the ADU?
Yes — treat the ADU as a second home. The structural inspection of the main house won't catch ADU-specific issues like inadequate egress, missing GFCI in a converted garage kitchen, or insufficient ceiling height in an above-garage unit. Ask the inspector to scope the ADU separately; expect $200–$400 extra.
Can I count the ADU rental income toward my mortgage?
Sometimes. Conventional Fannie Mae loans allow up to 75% of documented or projected ADU rent toward your debt-to-income calculation, but only if the ADU has a clean permit history and the appraiser identifies it as a legal accessory dwelling. Unpermitted ADUs typically can't be counted at all. FHA loans have stricter ADU rules; verify with your specific lender before assuming.
What's the biggest red flag when buying a home with an ADU?
An ADU that the seller is renting out but cannot produce a building permit for. This combines lower-tier risk (the unit may not meet current code) with upper-tier risk (the city can require you to demolish or vacate it post-closing). Always pull the permit history from the city's planning portal before final offer.
Should I pay a premium for a home with a permitted ADU vs. without one?
Usually yes, but verify the premium matches the local market. A 25–35% premium over comparable single-unit homes is typical in California metros; lower elsewhere. Run the rental-income math: if the ADU rents for $2,500/month and you're paying a $150K premium financed at current rates, the income covers the carrying cost in most markets — but appraiser comp gaps can leave you with a thin margin.
What if the seller built the ADU without permits?
Three paths: walk away, negotiate the price down to reflect the legal risk (typically -10% to -20% off comparable permitted-ADU pricing), or have the seller pull a retroactive permit before closing (often impossible if the unit doesn't meet current code). The third option is the cleanest but rarest. The second is most common in soft markets.
Considering a specific property?
Send us the address — we'll help you verify whether the ADU is permitted, what it's likely worth, and what to check before you close.