ChicagoGuide

How to read a Chicago zoning code

RS-3, B1-2, DX-16, RT-4A. Four parts do all the work, and one of them means something different in residential districts than everywhere else.

Every rule here is quoted or cited from the adopted ordinance, linked to Title 17 in our hosted zoning code. For the standards of one district, see the Chicago Zoning Field Guide.

Anatomy

The four parts of a district code

A Chicago zoning district is written as letters, a number, sometimes a dash and another number, and occasionally a letter on the end. Each part is a separate decision:

  1. The family letters — RS, RT, RM, B, C, D, M — say what kind of place the district is for, and which chapter of the ordinance governs it.
  2. The district number — the 1 in B1, the 3 in RS-3 — says which district within that family, and so which uses are allowed.
  3. The dash number — the 2 in B1-2 — is the bulk and density designation. It sets how much you may build, and it exists only outside the residential districts.
  4. A suffix — the A in RT-4A — marks a special standard layered onto the district.

The part that trips people up

In the business, commercial, downtown and manufacturing districts, the dash number is a genuinely separate instruction. The ordinance is explicit about it:

The same sentence appears for downtown §17-4-0401 and for manufacturing §17-5-0401. So B1-1 and B1-5 allow the same uses and very different buildings; B1-2 and B3-2 allow the same bulk and very different uses. Two independent dials.

Residential districts have no such dial. Chapter 17-2 defines no dash designation, because in an R district the number is part of the district’s name. RS-1, RS-2 and RS-3 are three districts, each with its own standards written into Chapter 17-2 — not one district at three intensities. The ordinance writes them closed up, as RS3, RT4 and RM5.5; the zoning map and everyone reading it add the dash.

Why it matters. “Can I get the dash number raised?” is a real question in a B or C district and a category error in an R district, where the only way up is a rezoning to a different district. See variations, special uses and rezoning.

The “A” suffix

One suffix is in general use. It may be applied only with RT-4, and it carries its own floor area and height standards §17-2-0105-C:

The families

What each set of letters is for

LettersDistrict family What it is forDash numbers
RS Residential Single-Unit (Detached House) Detached houses on individual lots, in areas already built that way. §17-2-0102 None
RT Residential Two-Flat, Townhouse and Multi-Unit Detached houses, two-flats, townhouses and low-density multi-unit buildings. §17-2-0103 None
RM Residential Multi-Unit Moderate- to high-density multi-unit buildings; RM-6 and RM-6.5 reach high-rise. §17-2-0104 None
B Business Storefront retail and service on pedestrian streets. B2 allows homes on the ground floor; B1 above it only. §17-3-0102 1, 1.5, 2, 3, 5
C Commercial A wider range of commercial uses than B, including those needing more traffic and parking. §17-3-0105 1, 1.5, 2, 3, 5
D Downtown Downtown only — DC core, DX mixed-use, DR residential, DS service. May not be applied outside the downtown boundary. §17-4-0101 3, 5, 7, 10, 12, 16
M Manufacturing Manufacturing, warehousing and industry outside the Central Area, M1 lightest to M3 heaviest. §17-5-0101 1, 2, 3
POS Parks and Open Space Public parks, open space and natural areas. §17-6-0200 None
T Transportation Transportation facilities and rights of way. §17-6-0300 None
PMD Planned Manufacturing District Industrial land protected from residential encroachment; each PMD carries its own rules. §17-6-0400 Numbered individually
PD Planned Development Not a district so much as a negotiated plan: bulk and density are set in an approved ordinance, parcel by parcel. §17-8-0100 Numbered individually

Paraphrased from each chapter’s district-description section, linked in the row. Dash numbers are those the chapter’s bulk and density section allows to be combined with the district. Every district’s actual standards are on its own page in the field guide.

Two entries are not really districts in the same sense. A planned development replaces the district tables with a negotiated plan, which is why the map shows a bare number like PD 30 and why no reference page can tell you what it allows. A planned manufacturing district is a base district, but each one is written individually to keep industrial land industrial.

The numbers

Three limits, and the one that binds

Once you have the district, three standards decide the building. They are independent, they run out at different moments, and the one that runs out first is the only one that matters:

StandardWhat it limitsThe arithmetic
Floor area ratio How much building the lot may hold: floor area divided by lot area. §17-17-0305 Lot area × FAR = the square feet you may build.
Minimum lot area per unit How much land each dwelling unit must have under it. §17-17-0304 Lot area ÷ the standard, rounded down = the unit count.
Maximum building height How tall, measured to the top floor’s ceiling on a flat roof or to mean roof height on a pitched one. §17-17-0311 A ceiling in feet, not floors — floor-to-floor heights decide how many fit.

Measured as Chapter 17-17 says to measure them, which is not always as you would guess — floor area excludes required parking §17-17-0305-B, and height stops at the top floor’s ceiling rather than the roof §17-17-0311-A.

A fourth limit is not a number at all: the required setbacks, which take ground off every side before the first of the three applies. On a narrow lot that is frequently the binding one. See what all four do to a real rectangle in the standard Chicago lot.

Then the overlays

What the code on the map leaves out

The district is where the answer starts. Sitting on top of it are rules that the map’s letters and numbers do not mention at all, each triggered by where the lot is rather than by how it is zoned:

Which of them reach a particular neighborhood is worth knowing before you read a district code there at all — the neighborhood guides count them lot by lot.

Questions

Common questions

What does the number after the dash in Chicago zoning mean?

It is the bulk and density designation. In the B, C, D and M districts the numeral following the dash sets the floor area ratio and, where homes are allowed, the minimum lot area per unit — so B1-2 is the B1 district with the dash 2 bulk standards (§17-3-0401). A higher dash number means more floor area. Residential districts have no dash designation.

Why does RS-3 have a number if residential districts have no dash designation?

Because in R districts the number is part of the district name rather than a separate instruction. RS-1, RS-2 and RS-3 are three different districts, each with its own bulk and density standards written into Chapter 17-2. In B1-2 the "B1" and the "2" are two independent choices; in "RS-3" they are one name. The ordinance itself writes these without the dash — RS3, RT4, RM5.5 — while the zoning map and everyday use add it.

What does the A in RT-4A mean?

The "A" suffix marks special standards for multi-unit buildings containing accessible dwelling units. It may be applied only in combination with RT-4, through the ordinary rezoning procedure, and it changes the floor area ratio and height standards; otherwise the district behaves as RT-4 does (§17-2-0105).

What is the difference between B and C districts in Chicago?

Both accommodate retail, service and commercial uses. The B districts are shaped for storefront streets oriented to pedestrians; the C districts take a wider range of commercial uses, including those that need more traffic and parking than a storefront street can carry. Within each, the district number (B1, B2, B3) sets which uses are allowed and where homes may go, and the dash number sets the bulk.

How do I find the zoning district for a Chicago address?

The city publishes an official zoning atlas, and the district is stamped on the map for every parcel. LotGrade reads it from the parcel record and applies the district and its overlays to the lot. A parcel inside a planned development shows a PD number instead of a district code, because its rules live in the approved ordinance rather than in the district tables.

Which chapter of the zoning ordinance covers my district?

Residential districts are Chapter 17-2, business and commercial are 17-3, downtown is 17-4, manufacturing is 17-5, the special purpose districts (POS, T, PMD) are 17-6, and planned developments are 17-8. Chapter 17-17 defines the terms and the measurements every one of them relies on.

Keep reading

For a real address

Check the real numbers for a real parcel

LotGrade reads the district, the dash number and every overlay against one Chicago address, and draws what they leave you to build.

Analyze a Chicago address Book a walkthrough

The analyzer requires an account — you’ll be asked to sign in. The Zoning Field Guide, the zoning code and these guides are free and need no login.