Coach houses are the only single-family dwellings in the Gold Coast reserved for middle-class mortals. There are plenty in the neighborhood, attached to a good number of old mansions, but those who own one clench it tight. There are only two on the market in the area at the moment, and one has gone under contract six days after listing for $500,000. It is a 1,000-square-foot two-bed behind a duplexed town house on Dearborn Street. The other is a $400,000 one-bed behind a condo-converted mansion directly across the street.

The new two-bed coach dates to 1875 and has been a living space longer than anyone can remember. “You can’t build coach houses from scratch in Chicago,” says @properties listing agent Mary Hanburger. “They have to be pre-existing, which is why they are concentrated in older affluent areas like the Gold Coast.”

A lot of coach houses belong to condo associations, with a nominal assessment for grounds maintenance but complete autonomy otherwise. With the featured home, $7 a month covers it. The shared amenity is the front courtyard separating the two duplexes in the main home from the coach house. Grooming and planting is up to the owners, namely the coach house’s occupant since private balconies gently discourage duplex owners from treading on the courtyard. A stone-pillared pergola, slate steps, ivy blanket, a proper front porch, and alley entry all help define the home. A corridor through the main home’s basement links the coach house to Dearborn and makes it easier for visitors to find. Rental parking is available in the building next door—a common compromise in the Gold Coast.

The seller, Dolores Hansen, purchased 16 years ago and performed a gut renovation. She layered dark hardwoods, built-in shelving, and French doors into a roomy, high-ceilinged living area. Stainless steel appliances and a laundry nook improved upon the small galley kitchen, and upstairs skylights replaced the natural light blotted out by peak ivy cover.

I can’t tell you much about the prospective buyer, because contracts are hashed out in private, but I’m not surprised this property found a suitor almost immediately. It differs in a few critical ways from the unsold coach house across the street: It’s a standalone structure (rather than at the end of a three-unit row), there’s an extra bedroom, and the monthly assessment is negligible ($7 versus $313). In light of all this, the extra $100,000 in asking price would be worth it to a lot of buyers. I predict good things for the other coach house, too, which has been on the market for about ten weeks, especially considering the next cheapest Gold Coast single-family is a 1970s town house asking $880,000.