Should I build an ADU before selling or sell the house as it is?

Building an accessory dwelling unit before selling only pays off if the added square footage and income potential outweigh construction cost and permitting time. Local zoning determines whether an ADU is even allowed on a given lot, and a project that runs past a planned listing date can cost more in carrying costs than it adds in value. Selling the house as is and letting a buyer add an ADU themselves is often simpler, and comparable sales with and without one nearby show which route nets more.