Zoning fundamentalsExplainer

Setbacks, explained

A setback is the strip along each property line where a building may not go. Front, side and rear setbacks together carve the buildable footprint out of the lot — and in Chicago, the front one depends on your neighbors.

buildable widthlot widthside setbacks

buildable depth = lot depth − front setback − rear setback

Worked example: a standard 25 × 125 ft Chicago lot zoned RS-3 with a detached house. The definitions and rules are Chicago’s, cited to Title 17 and linked to our hosted zoning code. Other cities use different terms and formulas; the “Elsewhere” notes point out where.

Definition

What a setback is

In Chicago’s ordinance, a setback is required open space between a building and a property line. It has to stay unobstructed from the ground to the sky, apart from a short list of allowed projections. Every lot has three kinds:

  • Front setback — along the street, across the full width of the lot §17-17-0261.
  • Rear setback — along the back property line, usually the alley §17-17-02140.
  • Side setbacks — along each side line, running between the front and rear setbacks §17-17-02157.

Don’t confuse it with a yard. Chicago defines a yard as the actual open space on a lot, “as opposed to ‘required’” §17-17-02192. A setback is the rule; a yard is what is on the ground. Houses built before today’s code often have yards smaller than the setback a new building would need.

Measurement

How setbacks are measured

Setbacks are measured square to the property line, but not all to the same part of the building:

  • Front: from the front property line to the building’s exterior wall §17-17-0306-A.
  • Side and rear: to the furthermost projection of the structure, ignoring the features allowed to encroach §17-17-0307-A §17-17-0308-A.

Averaged front setbacks

Many cities fix the front setback at a number. Chicago often doesn’t: new buildings line up with the houses already on the block. In the RS districts, the front setback is the average of the existing front yards on the nearest two lots on each side, after dropping the one with the shallowest yard §17-2-0305-A.

A block of five 25-foot lots seen from the street, with the neighboring houses shown as footprints. The four neighbors sit 18, 22, 14, 20 feet back. Dropping the shallowest (14 feet) and averaging the rest gives the middle lot a 20 foot front setback; its required yards are shaded and its 20 by 70 foot buildable area is outlined. 18 ft22 ft14 ft ✕20 ft20 ft
Four neighbors sit 18, 22, 14, 20 ft back. The 14 ft yard is the shallowest, so it is dropped; the other three average to 20 ft, the middle lot’s front setback. Its required yards are shaded; the dashed outline is what’s left to build on. Neighboring houses are drawn as footprints.

In RT, RM and DR districts the builder chooses: the fixed standard of 15 ft, or 12% of lot depth if that is less, or the neighbor average §17-2-0305-B. On a primary boulevard the average is mandatory and has no cap. If a neighbor is vacant it counts as 20 ft or 16% of depth in RS districts, and 15 ft or 12% elsewhere §17-2-0305-C.

Method

Working out the buildable footprint

For the middle lot in the drawing, a 25 × 125 ft RS-3 lot with a detached house:

Front setbackaverage of 18, 22, 20 ft — §17-2-0305-A
20 ft
Side setbacks20% of 25 ft combined, neither under 2 ft — §17-2-0309-A
2 + 3 ft
Rear setback28% of 125 ft, capped at 50 — §17-2-0306-B
35 ft
Buildable area25 − 5 wide × 125 − 20 − 35 deep
20 × 70 ft
Largest footprintbefore height and FAR
1,400 sq ft

That is the ceiling on the footprint, not the building. The height limit decides how many floors stack on it and floor area ratio caps the total: RS-3’s FAR of 0.9 on this 3,125 sq ft lot allows 2,813 sq ft, almost exactly two full floors of 1,400.

Corner, through and reversed corner lots follow different rules for which side is the front and where the rear setback goes. See lot types.

Encroachments

What can go inside a setback

“Unobstructed from the ground to the sky” has exceptions. Chicago’s list of allowed encroachments §17-17-0309 says, for each feature, whether it may sit in the front, side or rear setback. A selection:

Street side

Front setback

The street side of the 25-foot lot with its required yards shaded: a bay window projects 3 feet into the front setback. bay windowfront setback

A bay window may project up to 3 ft if its lowest point is at least 4 ft above grade. Eaves may project 18 in anywhere, or 3 ft into front and rear setbacks.

Alley side

Rear setback

The alley side of the same lot: an open porch projects into the rear setback and a detached garage sits in it, 2 feet from the alley line. open porchgaragerear setback

Garages, coach houses, sheds and porches open on three sides may all sit here. An alley-loaded garage or coach house stays 2 ft off the rear line unless it is 10 ft or more from the alley centerline.

Required setbacks are shaded. The rear setback is by far the most permissive of the three. Heights are drawn exaggerated ×1.6.
FeatureFrontSideRear
Eaves and gutters, 18 in or lessYesYesYes
Eaves and gutters, 3 ft or lessYesNoYes
Bay windows, ≤ 3 ft and ≥ 4 ft above gradeYesNoYes
Chimneys, ≤ 18 inYesYesYes
Cornices and similar features, ≤ 3 ftYesYesYes
Porches and balconies open on 3 sidesNoNoYes
Garages and coach housesNoNoYes
Air conditioners, ≤ 4 ft tallNoYesYes
Solid fences up to 4½ ftYesYesYes
Steps ≤ 6 ft above grade, accessibility rampsYesYesYes

Selected rows from §17-17-0309. The full table covers fences, parking, patios, stairs, satellite dishes and more, with conditions.

Watch the shallow-block trap. If the averaged front yard comes out at half the fixed front setback or less, none of the front encroachments apply §17-2-0305-E. On a block of houses built close to the sidewalk, even the bay window is out.

Chicago

Setbacks in Chicago

Chicago’s residential setbacks are set per district in Chapter 17-2. In business and commercial (B and C) districts there is generally no front or side setback unless the lot abuts a residential district, but floors with dwelling units need a 30 ft rear setback §17-3-0404.

DistrictFrontSideRear
RS-1Average of neighborsCombined 30% of lot width; each side ≥ 5 ft or 10%28% of depth (≤ 50 ft)
RS-2Average of neighborsCombined 30%; each side ≥ 4 ft or 10%28% of depth (≤ 50 ft)
RS-3Average of neighborsCombined 20%; each side ≥ 2 ft or 8%28% of depth (≤ 50 ft)
RT-3.5 – RM-5.515 ft or 12% of depth (lesser), or the averageCombined 20%; each ≥ 2 ft or 8%; none over 5 ft30% of depth (≤ 50 ft)
RM-6, RM-6.515 ft or 12% of depth (lesser), or the averageNone if coverage ≤ 50%; otherwise 10% of width or height (≤ 20 ft)30% of depth (≤ 50 ft), from 18 ft up

Residential districts, principal residential buildings (townhouses follow §17-2-0500). Rear figures are for buildings other than detached houses unless shown; detached houses use 28% in every R district. Sources: §17-2-0305, §17-2-0306, §17-2-0309.

Two details that change the answer

  • Street or alley on the side. In RT and RM districts a side that abuts a street or alley needs no setback, but the other side must then be at least 10% of the lot’s width §17-2-0309-A.
  • Taller RM districts. In RM-5 and RM-5.5 the rear setback only applies from 6 ft above grade, and in RM-6 and RM-6.5 from 18 ft §17-2-0306-D §17-2-0306-E — so a ground-floor garage can run to the alley.

Getting a smaller setback

The Zoning Administrator can approve a reduction of up to 50% in any setback when it matches the prevailing yards on the block §17-13-1003-I, and a side setback reduction of up to 50% for a 20-foot-wide house on a lot 24 ft or wider §17-13-1003-H. Beyond that, the route is a variation from the Zoning Board of Appeals — see zoning relief in Chicago. Each district page in the Field Guide lists its own setbacks.

Questions

Common questions

What is the difference between a setback and a yard?

It depends on the code. In Chicago, a setback is the open distance the ordinance requires between a building and a property line, and a yard is the open space that actually exists (§17-17-02152 and §17-17-02192) — which matters because an RS front setback is calculated from the neighbors’ existing yards. New York City reverses the vocabulary: its “yards” are the required open areas, and “setback” usually means an upper-story step-back.

How is a front setback calculated in Chicago?

In RS districts it is the average of the existing front yards on the nearest two lots on each side, after dropping the shallowest one (§17-2-0305-A). In RT, RM and DR districts the owner may use either 15 feet (or 12% of lot depth, if less) or the average of the nearest two lots on each side — all four of them, since dropping the shallowest is an RS step only — except on a primary boulevard, where the average is mandatory (§17-2-0305-B). A vacant neighbor counts as 20 ft or 16% of its depth, whichever is less, in RS districts and 15 ft or 12% elsewhere (§17-2-0305-C). Lots across a street or an alley are never counted.

What is the rear setback for a house in Chicago?

For a detached house in any R district, 28% of lot depth or 50 feet, whichever is less (§17-2-0306-B). On a standard 125-foot lot that is 35 feet. Other residential buildings use 30%, or 24% for smaller buildings with at least a third of the units accessible.

Can a garage or coach house be built in the rear setback?

Yes. Garages and coach houses are among the features allowed in a required rear setback (§17-17-0309), but an alley-loaded one must stay 2 feet off the rear property line unless it is at least 10 feet from the alley centerline.

Can I build closer to the lot line than the setback allows?

Sometimes. Chicago’s Zoning Administrator can reduce a setback by up to 50% when that matches the prevailing yards on the block (§17-13-1003-I), and larger reductions go to the Zoning Board of Appeals as a variation. See the guide to Chicago zoning relief.

Do eaves, bay windows and porches count against the setback?

Not if they fit the list of allowed encroachments in §17-17-0309 — eaves up to 18 inches anywhere, bay windows up to 3 feet into front and rear setbacks, and open porches in the rear. One catch: if the averaged front yard is half the fixed setback or less, no front encroachments are allowed (§17-2-0305-E).

Keep reading

For a real address

Check the real numbers for a real parcel

An averaged front setback depends on the actual houses next door. LotGrade finds the neighboring lots for any Chicago address, applies the district’s side and rear rules to the real lot dimensions, and draws the buildable envelope.

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