Now that coach houses are legal again across most of Chicago, the first question nearly every homeowner asks is a simple one: what does one actually cost? The honest answer is a wide range, and the reasons it's wide are exactly what you need to understand before you plan a project. A detached backyard unit is not the same purchase as a finished basement apartment, and treating them as interchangeable is how budgets blow up.
The city's permanent Additional Dwelling Unit (ADU) ordinance took effect on April 1, 2026, opening backyard and basement units to roughly 60 percent of Chicago after decades of prohibition. If you're still working out whether your property qualifies at all, start with our Chicago citywide ADU ordinance guide, which covers the ward opt-in map and eligibility. This piece is about the money.
The Short Answer: Two Very Different Price Tags
Chicago's code splits ADUs into two categories, and the split drives almost everything about cost:
- Conversion units (a finished basement or attic apartment) run roughly $65,000 to $150,000. You're finishing space that already exists, so there's no new foundation and no new roof.
- Coach houses (new detached construction, usually in the backyard where a garage sits) run roughly $150,000 to $350,000 and up, or about $200 to $400 per square foot for a typical 500 to 700 square foot unit. Several early adopters in the city's pilot program reported all-in coach house costs landing around $300,000.
During the pilot, conversions outnumbered coach houses by more than two to one, and the price gap above is the reason why. If your goal is the lowest cost to a rentable unit, a conversion almost always wins. If your goal is privacy, a separate entrance, and stronger rent, the coach house earns its premium. It's the same tradeoff Seattle homeowners weigh between an attached ADU and a detached DADU.
Why a Coach House Costs More Than a Basement
The per-square-foot number climbs for a detached unit because you're building a small, complete house from the ground up. A coach house needs its own foundation, framing, roof, exterior envelope, and separate utility connections. A basement conversion inherits all of that from the building it sits inside.
Two Chicago-specific rules add cost to the coach house side of the ledger that a conversion largely avoids:
- The apprenticeship mandate. Any contractor building a new coach house must be enrolled in a U.S. Department of Labor-recognized apprenticeship program. Conversion units are exempt. This narrows the pool of eligible builders, and a smaller pool tends to mean firmer pricing.
- Architect-stamped drawings. New detached construction in Illinois generally requires permit drawings stamped by a licensed architect. That's real design cost that a straightforward basement finish may not trigger.
The ordinance also caps coach house height at 22 feet, measured to the highest point, which limits how much you can build up on a small lot and pushes some designs toward a single story.
The Line Items That Move Your Number
Two coach houses of the same square footage can cost tens of thousands of dollars apart. The variables that matter most:
- Site and utilities. Running water, sewer, gas, and electric service to a detached structure at the back of a lot is one of the biggest swing costs. A long trench or an undersized existing service raises the bill fast.
- Foundation and grade. Chicago's older lots and alleys aren't always level or easy to access, and difficult site conditions add both time and money.
- Whether you're replacing a garage. Many coach houses go up where a garage stood. Demolition, and whether you preserve parking underneath, changes the scope.
- Finish level. The gap between builder-grade and high-end finishes can be $50,000 or more on a unit this size.
- Design and permitting fees. Architect drawings, the two-stage city review, and any ward-specific conditions all carry cost before a single wall goes up.
Prefabricated and panelized coach houses have started appearing in the Chicago market at lower entry points, but availability and quality vary widely, so vet a modular builder as carefully as any site-built one. Before you commit to any route, get a detailed, itemized estimate rather than a round number. Our how to budget for an ADU guide walks through the line items that most often surprise first-time builders, and if your project starts at an existing garage, the garage conversion guide covers the structural realities either way.
Budget for Time, Too
Cost isn't only dollars. Chicago runs a two-stage approval process: first a pre-certification with the Department of Housing to confirm your property qualifies, then a building permit with the Department of Buildings. Realistically, plan for four to six months from application to permit approval, then another four to ten months of construction. Front to back, most projects run close to a year, and every extra month of design revisions or financing delay is carrying cost you're paying for.
Demand is already ahead of supply. By mid-March 2026, before the ordinance had even taken effect, the Department of Housing had pre-certified 816 additional dwelling units, with the early activity concentrated on the North and Northwest sides. Qualified coach house builders who meet the apprenticeship requirement are a small pool, and a small pool books up. Starting now protects both your timeline and your price.
How to Keep the Number Honest
A few disciplines keep a coach house budget from drifting:
- Confirm eligibility before you spend on design. Check the city's official ADU eligibility map first. Paying for architect drawings on a lot that turns out not to qualify is the most expensive mistake you can make.
- Get itemized bids, not ballparks. A single all-in figure hides the site and utility costs that vary most.
- Verify the apprenticeship credential in writing. Ask any coach house builder to show enrollment before you sign. This is exactly the kind of thing to raise when you interview a builder.
- Finance a real estimate, not a guess. Line up your funding around a detailed bid so you're not scrambling mid-project.
Find a Chicago Coach House Builder
The hard part in Chicago isn't the rules anymore. It's finding a builder who has actually delivered a coach house or conversion under the new ordinance, meets the apprenticeship requirement, and knows the ward-by-ward opt-in map. That pool is small but growing fast.
We're building a verified directory of Chicago ADU and coach house builders at adubuilderschicago.com. Check your eligibility first, then head there to get on the list and connect with builders working under the 2026 ordinance.
Sources: WTTW News, Block Club Chicago, and the City of Chicago Department of Housing ADU program. Costs are planning ranges, not quotes, and vary by site, unit type, and finish level. Ordinance details and ward opt-in status change over time; always confirm your property's status on the city's official ADU eligibility map before planning a project.