Chicago zoning comparison · the two two-flat/townhouse districts
RT-3.5 vs RT-4: which lets you build more?
RT-4 carries the larger envelope — FAR 1.2 vs 1.05; on a standard 25 × 125 ft Chicago lot, RT-4 permits 3 units by right against 2; the height limits are 38 ft vs 35 ft.
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 →
Side by side
| RT-3.5 Residential Two-Flat, Townhouse 3.5 | RT-4 Residential Two-Flat, Townhouse 4 | |
|---|---|---|
| Max FAR | 1.05 | 1.2 |
| Max height | 35 ft | 38 ft |
| Lot area per unit | 1,250 sf | 1,000 sf |
| Units on a standard 25×125 ft lot | 2 | 3 |
| Min lot area | 2,500 sf | 1,650 sf |
| Residential parking / unit | 1 | 1 |
| Max lot coverage | 50% | 55% |
| Permitted uses | two-flats, townhouses and small apartment buildings | two-flats, townhouses and multi-unit residential |
| Connected Communities bulk bonus tier | No | No |
Green marks the more permissive value. Setbacks are contextual in both districts and omitted here — see the district pages for the working scalars and the governing formulas.