The ADU rent that qualified me was $350 above what it actually leased for

The 75 percent you got hit with is a lender overlay layered on top of the agency rule, and overlays differ shop to shop. I've read two lender matrices on this in the last few months and one of them wanted the ADU to be legal and separately permitted on the county record before any income counted at all, which yours apparently did not require or your studio already cleared. Ask for the matrix page, not a verbal answer from a loan officer. The page is what underwriting works from.

How did you find out the factor was 75 percent, did they volunteer it or did you have to ask?

$6,200 on a subpanel, a lock, and a cooktop is not scope creep, that's just the punch list you inherit on a converted garage. Scope creep is when the subpanel opens up and the electrician says the feeder to the garage was undersized from 1974 and now you're trenching the yard. You got off cheap. Did anyone look in that panel during your inspection?

I read the cause differently than you do. The $350 rent gap cost you $4,200 a year. The 47 percent DTI is what turned a $4,200 miss into a reserve wipeout. You closed with no room, so the first two unbudgeted things became debt. I've made the same mistake and my fix wasn't better rent estimates, it was refusing to close unless six months of full payment sat in an account I wasn't allowed to touch. Better estimates help. They don't save you when the water heater goes.

An agent can also pull a rental CMA off the local MLS for you, and in my market the rental data is thin enough that it's worth doing alongside the manager opinions. Different sources, same question.

My rule on accessory units is to take the lowest of three independent rent opinions and then apply 80 percent to that, and to model eight weeks of vacancy in year one because a first lease-up on a unit with no rental history always takes longer than a re-lease. Run your deal through that: lowest quote probably $1,300, times 0.8 is $1,040, minus eight weeks gets you to about $880 a month for year one. That's within a hundred dollars of what you actually collected. The math was available before closing.

Sextant's 80 percent of the lowest quote is close to what I use and it feels absurdly conservative right up until the year it isn't. Arbor, my basement unit taught me the separate entrance matters more to rent than square footage does. Tenants price privacy. Does your studio share the driveway approach with your front door?

Seven weeks empty on a studio in fall tracks with what I see. Studios turn more often than one bedrooms and they turn to people who are moving for work, which is seasonal. If you ever furnish it, the tenant pool changes and so does the vacancy pattern, though the wear does too.

The version of this I did was to wait. Not helpful to you now. But the studio isn't going anywhere and neither is the rent, and in three years the $350 gap is a rounding error against the loan you're paying down.

Vacancy factors and reserve requirements on this vary by lender and they change, so anyone reading should get the current terms in writing before they build a max price around projected ADU income. The mechanism itself is straightforward: the underwriter takes a discounted rent figure, adds it to your qualifying income, and the cap limits how much of the total can come from that source. What arbor found out is that the number they add to your income has nothing to do with the number a tenant will pay.

Worth saying that the gap is proportionally worse at low price points. Where I look, an ADU rents for $700 and a $200 appraisal miss is 28 percent of the income. There's no cushion to absorb it.

What is the rent schedule you both keep mentioning, is that a separate document from the appraisal or part of it? I want to know what to ask to see.

Would you do it again? Not the same deal, the same strategy. That's the part I'm weighing.

On the seven weeks, was the studio listed at $1,650 for part of that? I ask because if you held the appraiser's number for three weeks before dropping, some of that vacancy is the price and not the market.

Wren's question is the one I'd want answered before agreeing the appraiser was wrong. Chasing the market down from an ask you inherited from an appraisal costs weeks. On the reserve point, I hold four months of full payment per door now and I got to that number the same way arbor did, by not having it once.