By Steven Vance with help from Spencer Blaney, R.A.
Chicago adopted a modernized building code this year that implements the organization, concepts, and many of the standards in the model International Building Code (2018 version). While projects that are designed to the updated Chicago building code (CBC) can't be submitted until December 1, it's important to start understanding how the updated CBC will change the standards for certain residential project types.
Chicago is adopting the IBC's occupancy classifications. Those follow the Sesame Street naming method: "R" for residential, "M" for mercantile, and so on. Current CBC puts residential buildings in the "A" group.
Within the IBC "R" occupancy group, there are four classifications, which can be summarized:
R-1: Temporary lodging (hotels and motels, etc.)
R-2: Multi-unit housing (apartments and condos, SROs, dorms with more than 16 residents, etc.)
R-3: Single-family and small multi-unit housing (smaller versions of some buildings in R-2, plus two-flats)
R-4: Smaller, supervised supportive and transient housing (assisted living, group homes, rehabilitation centers; larger versions of these housing types are in the "I" Institutional occupancy group)
In current CBC, the A-1 occupancy classification includes single-family houses and group homes with up to 15 people, while A-2 includes multi-unit buildings, among other uses. In the updated CBC, residential occupancies will start with "R" instead of "A". There is not a direct translation between Chicago's current "A" classifications and the IBC's "R" classifications.
Chicago will add one residential occupancy classification, which is not part of the model IBC: R-5.
The R-5 occupancy is added in section 310.6 of the updated CBC, and is defined as:
...buildings with no more than four stories above grade plane containing one, two or three dwelling units (including live/work units), with or without an attached private garage, and no other occupancy, where each dwelling unit is primarily occupied on a non-transient basis by a single household. Group R-5 shall also include accessory buildings with no more than two stories above grade plane located on the same lot as Group R-5 dwelling units.
In short, Chicago's new R-5 occupancy classification includes:
all single-family houses, two-flats and three-flats, and up to three townhouses for permanent residents – all up to four stories
accessory buildings on the same lot, like coach houses and garages, up to two stories.
R-5 doesn't allow for mixed-use or mixed-occupancy buildings. All R-5 buildings would be considered A1 or A-2 in the current CBC and R-2 or R-3 in jurisdictions that use IBC.
Why did Chicago add R-5
Generally speaking, the standards that IBC applies to R-2 buildings (three-flats and up) and R-3 buildings (single-family and two-flats) doesn't conveniently accommodate the design and construction characteristics common in the tens of thousands of existing two and three-flats in Chicago.
Differences between IBC and updated CBC
There are many differences between unmodified R-2 and R-3 standards in IBC 2018 and the updated Chicago building code for those same buildings that would be classified as R-5:
R-5 applies many standards to three-flats that IBC would only apply to single-family and two-flats
R-5 buildings of Type V construction (exterior wood frame construction) are not required to have sprinklers, unless they have 4 stories (see table 504.4)
Some R-5 buildings have a lower fire resistance requirement for floors over basements (refer to section 605.4 and table 601)
R-5 buildings with three or fewer stories have a reduced guard rail height minimum (see section 1015)
R-5 doesn't have seismic design standards (see section 1613.1)
The updated CBC will continue to allow winder treads (turned stairways) (see section 1011.5.3)
Using the updated CBC becomes optional for architects and builders on December 1, 2019, and required on August 1, 2020.