Mixed-use gets underwritten badly in a specific, recurring way: whichever asset class the buyer knows best colonizes the model. The multifamily buyer treats the ground-floor retail as a rounding item, a little extra income with a cap rate stapled to it. The retail buyer treats the units upstairs as a rent-times-twelve annuity. Both are running one model where the building requires two, because the components do not just differ in detail. They differ in the rules.
The residential component runs on multifamily physics: unit mix, loss to lease, annual leases, turnover measured in days, demand that is broad and statistical. The retail component runs on commercial physics: a handful of specific tenants on multi-year leases with personal probabilities, rollover events that cost real money and take real time, recovery structures, co-tenancy exposure, downtime measured in quarters. Blending them produces category errors in both directions, and the most expensive one is familiar: applying residential vacancy instincts to commercial space. An apartment turning is a two-week make-ready. A restaurant space going dark is a year of downtime, a tenant improvement package, and a leasing campaign, and a model carrying five percent vacancy across both components has priced the second event as if it were the first.
The retail component also deserves its own risk reading, because ground-floor retail under apartments is its own niche. The tenant pool skews to neighborhood service and food users whose survival depends on the immediate trade area, sometimes substantially on the residents upstairs, which quietly correlates the two components: the residential lease-up struggles and the coffee shop's sales struggle with it. Small-format spaces in residential buildings can also be genuinely hard to lease, oddly configured, venting-constrained, parking-thin, and a vacant retail bay dragging on an otherwise healthy building is one of the most common mixed-use surprises. Underwrite the retail suite by suite, with commercial rollover economics, exactly as if it stood alone, because economically it does.
Then there is the blending question at exit, which deserves more suspicion than it gets: who buys this building, and how do they price it? Mixed-use frequently trades to the buyer pool of its dominant component, with the minority component discounted below its standalone value, and an underwriting that capitalizes each component at its own market cap rate may be modeling a buyer who does not exist. The honest exit assumption prices the building the way its actual buyer pool will, which is a question worth answering before the purchase rather than during the sale.
PropCalc™ runs multifamily and retail on the same underwriting engine with each component keeping its own rules, unit-level on one side, lease-level on the other, one capital stack over both. Which is the whole discipline in a sentence: one building, one debt, one exit, two models, and no borrowed assumptions between them.