Dissecting the Modernized Chicago Building Code: Chapter 2

Christopher E. Chwedyk, CSI, AIA

Posted by Christopher E. Chwedyk, CSI, AIA

Phase two of Modernizing the Chicago Building Code is in full force. We previously shared information on the new Chicago Administrative Provisions that was implemented on July 1st. The next step in the process includes publishing the new Chicago Building Code. The new CBC will publish in October 2019. It’s key to note that each Code will be published separately. Until the codes are published, we are referencing the ordinance that passed in April 2019. To follow along, you can download the ordinance here.

Refining the Definitions

Chapter 2, definitions and measurements, of the building code is worth diving into as this chapter will include significant changes that will be an adjustment to Chicago based users. These changes will better align with the International Building Code (IBC) and will help avoid discrepancies. Some definitions will be cross-referenced between codes instead of being repeated in each code. The general rules on definitions begin on pg.163 and will explain how they’ll be applied as well as where to find guidance on what the terms mean.


In 202. Definitions start on pg.163 where one can find some of these notable changes:

Deck vs. Exterior Balcony vs. Porch:

Chicago Specific Definitions to note important differences in each Building Element. This helps us better interpret the code per each scenario

  • Deck - An open, unroofed and uncovered floor structure, other than an occupiable rooftop, designed or used for more than incidental occupancy, which may or may not include an exterior means of egress.
  • Exterior Balcony - An exterior floor structure, other than an occupiable rooftop, that is attached to the exterior wall of a building, with all means of egress requiring travel through the building, and that is open to the atmosphere on at least one side.
  • Porch - An unheated roofed or covered structure, containing a stairway used for ingress and egress and additional floor space, that is separated from heated areas of the building by a fire-resistance rated exterior wall and unprotected openings (Open Porch/Enclosed Porch)
Fire separation distance:

Slightly different than the IBC(International Building Code)

  • It’s more generously defined in Chicago
  • Model code notes measured to the far side of the street when facing street or public way vs. to the Centerline
  • Chicago notes: measured to closest abutting property line, far boundary of a public way adjoining the lot, or an imaginary line between 2 buildings on the same lot. It also allows distance to be measured at right angles from the face of a wall or *edge of a building element.

Will be most helpful if done in order

  • Attic (pg. 165): Unfinished occupied space, If certain conditions are met, it will not be counted as a story
    • 81” or more between top of ceiling framing and underside of the roof structure considered additional story
  • Basement (pg. 166): Something other than story above grade plane
  • Lofts: (pg. 177/Rules: Section 1207.5, pg. 353)
    • Level located above the main floor level within dwelling or sleeping unit, open to the main floor on at least one side and used as a living or sleeping space
    • They’re barred from the International Residential Code
    • There are provisions for tiny houses, allowed in a range of conditions
  • Mezzanine: (rules: section 505, pg. 221) similar conditions to lofts, but larger
    • Chicago limitations: 20%
  • Penthouse: (pg. 171/Rules: Section 1510/1513)
    • Occupied penthouses - generally count as a story
      • Removed word “unoccupied” in New Code
    • Mechanical penthouses/vertical circulation elevators and stairs - maybe excepted from being considered a story

Story:(pg. 184)

Story above grade plane:(pg. 185) differentiates from “story”

Telecommunications equipment area:

Replaces technology center

  • Technology center - office space that uses computers
    • This definition covers: server rooms inside of office spaces/server farms, which will have slightly different hazards.


In 203. Measurements begin on pg.187 where one can find building height, building area and other key measurement features and updates.

Building Height (pg. 187-188):

Will be different from what the previous building code listed.

  • Closer to zoning measurement but still different - it is not building HEIGHT
  • Measures to underside of roof structure at the highest story
    • Notes that it is measured to the mean elevation of the highest roof plane vs. to the highest point of the building (old CBC)
  • No exceptions for dormers
  • Mean roof height (structural code) is not building height.
6 Exceptions that apply to Building Heights
  1. Occupiable rooftop - measured to highest walking surface of occupiable rooftop above highest story
  2. Parapet > 42” - measured to top of parapet exceeding 42 inches above highest point of a low-sloped roof or occupiable rooftop
  3. Unoccupied Rooftop structures and rooftop access penthouses (ch.15) - not considered in building height measurements
  4. Certain dormers - without low-slope roof, are no higher than highest point of the roof plane and do not exceed ⅓ of the horizontal area of the roof plane, not considered in measuring building height
  5. Complex roofs - rooftop access penthouses and other structures with occupiable rooftops not considered when measuring building height
  6. Ignore up to 12” of CI above structural roof deck - highest roof plane of continuous installation and not > 12” above structural roof deck and required parapet walls, can measure building height to highest point of structural roof deck

Flat Roof:
The current building code measures to the highest point, the New Code will measure to the midpoint of the roof

Pitched roof:
The current building code measures to the highest point, the New Code will measure to the midpoint of the roof and exclude dormer if it meets exception 5

Building area:

  • Zoning: includes thickness of exterior walls; excludes parking & mechanical rooms up to a certain size.
  • Current Building Code: excludes thickness of exterior walls
  • New Building Code: Included covered porches, balconies, etc.


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Follow us as we discuss the revisions, additions, and deductions to the new CBC. Interested in learning more? Reach out to our team

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