Chicago zoning district · Residential Two-Flat & Townhouse
RT-3.5 zoning in Chicago: what you can build
RT-3.5 (Residential Two-Flat, Townhouse 3.5) is Chicago’s lower-intensity two-flat and townhouse district: it allows two-flats, townhouses and small apartment buildings, with a maximum floor area ratio (FAR) of 1.05, a height limit of 35 feet, 1,250 square feet of lot area required per dwelling unit. On a standard 25 × 125 ft lot (3,125 sq ft), that permits 2 units by right.
Figures originally read from a Title 17 excerpt in a third-party zoning report dated 18 September 2024. On 24 August 2026 the bulk standards — floor area ratio, lot area per unit, building height and minimum lot area — were re-checked against the current adopted edition 2026-S-73 and found unchanged. Setbacks and parking ratios were not part of that pass and still rest on the 2024 reading. Data snapshot generated 2026-08-24. How this data is produced and checked →
Where RT-3.5 is mapped
Zoom in for district codes
- Planned Manufacturing (PMD)
- Parks & Open Space (POS)
- Planned Development (PD)
- Downtown (DC/DR/DS/DX)
- Residential (RS/RT/RM)
- Business (B)
- Commercial (C)
- Manufacturing (M)
- Transportation (T)
- Other / unclassified
Zoning district boundaries: City of Chicago Data Portal. Basemap: © OpenFreeMap © OpenMapTiles © OpenStreetMap contributors.
RT-3.5 bulk & density standards
| Maximum floor area ratio (FAR) | 1.05 verified §17-2-0304-A, Municipal Code of Chicago |
|---|---|
| Maximum building height | 35 ft verified §17-2-0311-A, Municipal Code of Chicago |
| Minimum lot area | 2,500 sq ft verified §17-2-0301-A, Municipal Code of Chicago |
| Lot area per unit (density) | 1,250 sq ft / unit verified ≈ 34.8 units per acre §17-2-0303-A, Municipal Code of Chicago |
| Setbacks (front / side / rear) | 15.1 / 2 / 29.9 ft approximation Chicago setbacks are contextual formulas (averages of neighboring lots, % of lot width/depth). These are working scalars — confirm per lot. §17-2-0305..0309, Municipal Code of Chicago |
| Residential parking | 1 space / unit verified Before TOD / Connected Communities reductions. §17-10-0207-C, Municipal Code of Chicago |
| Maximum lot coverage | 50% approximation |
Verified figures match the ordinance table verbatim at the cited section. Approximation flags contextual formulas (setbacks that depend on neighboring lots, use-group-dependent parking) reduced to a working scalar — the ordinance formula governs.
Permitted uses
RT-3.5 allows two-flats, townhouses and small apartment buildings.
- two-flats
- townhouses
- small apartment buildings
Transit changes these numbers
Under the Connected Communities ordinance (§17-10-0102-B), transit-served lots can cut residential parking minimums — up to 100% by right within ½ mile of a CTA rail station or ¼ mile of a designated bus corridor (outside downtown districts), and up to 50% near Metra. Density and height bonuses, however, are reserved for -3 suffix B and C districts — a residential district like RT-3.5 keeps its base bulk standards. Full Connected Communities guide →
RT-3.5 — common questions
- Does RT-3.5 allow a two-flat?
- Yes, on a lot of at least 2,500 sq ft (the district requires 1,250 sq ft of lot area per unit).
- How many units can I build on a standard lot in RT-3.5?
- A standard 25 × 125 ft Chicago lot (3,125 sq ft) divided by the 1,250 sq ft lot-area-per-unit standard permits 2 units by right. Transit-served lots may qualify for Connected Communities density bonuses.
- How tall can I build in RT-3.5?
- 35 feet (§17-2-0311-A). Taller buildings need a variation, a planned development, or — on transit-served B-3/C-3 lots — the Connected Communities height bonus.
- Can I add a coach house or conversion unit in RT-3.5?
- Yes — the §17-2-0207 use table permits both by right in RT-3.5, citywide (no ADU-area restriction). A building that has lawfully existed 20+ years can add conversion units equal to 33% of its existing units — minimum one (§17-2-0303-C). Coach houses must meet the standards of §17-9-0201-F.
- Do parking requirements in RT-3.5 change near transit?
- Yes. The base requirement is 1 space per unit, but under the Connected Communities ordinance (§17-10-0102-B) lots within ½ mile of a CTA or Metra rail station — or ¼ mile of a designated bus corridor — can reduce residential parking minimums, up to 100% by right for CTA-rail- and bus-served lots outside downtown districts.