Why eighteen months of waiting was the best decision on a $131k prefab ADU cottage

A detached 480 square foot one bedroom, prefab shell set on a slab, finished and renting at $1,595, total spend $131,400 including site work, utility runs, permits, and the pad, is a fairly ordinary ADU outcome. What's worth studying is the eighteen months spent before anything got signed. A disciplined path through that stretch looks like this: reading the local ADU ordinance twice, then going to the counter and asking a plans reviewer to walk through it in person, which often corrects assumptions for free. Confirming the actual rear setback rather than assuming it, since a five foot setback instead of a commonly assumed ten foot one can change which part of a yard can hold the unit and preserve a mature tree. Getting three utility scoping quotes, since sewer connection is where these projects often blow up. A quote spread from roughly $9,200 to $23,000 for the same scope, depending on whether the route trenches the short way or the long way around the house, is not unusual. What tends to break a budget late is the electrical service. A 100 amp main panel often needs a full service upgrade to feed a second dwelling, which can run $6,800 or more and show up only weeks before the set date. Padding the budget by 15 percent and not spending that pad on finishes is what absorbs a surprise like that. Worth keeping: the padding, and the in-person visit to the permit counter. Both cost little or nothing. A unit like this can cover well over half of a primary mortgage payment, without needing to sound like more than it is.