Fire separation in multifamily buildings, drawn on the set
Dwelling unit walls and floors, corridors, shafts and exit stairs: the ratings the International Building Code sets for an apartment building, the reductions sprinklers allow, and where each lands on the drawings.
The code this guide reads
The figures below come from the 2021 International Building Code; check the edition your jurisdiction has adopted, since later editions can renumber or adjust a section. California adopts the IBC as the base of the California Building Code; the 2025 CBC took effect on January 1, 2026. Your jurisdiction's adopted edition and local amendments govern, so confirm each rating on your project's code analysis.
An apartment building is Group R-2. The rules below are the ones that shape almost every multifamily set: what separates one unit from the next, what separates units from the corridor, and what encloses the vertical openings that connect floors. The podium code guide covers the separate question of a podium building's horizontal building separation and its height and area limits.
Dwelling unit separations
Walls between units
In Group R-2, walls separating dwelling units from each other and from other parts of the building are fire partitions under IBC Section 708 (the requirement sits in Section 420.2). Fire partitions have a fire-resistance rating of not less than 1 hour.
The code allows a reduction: in buildings of Types IIB, IIIB and VB construction equipped throughout with an automatic sprinkler system under Section 903.3.1.1 (NFPA 13), dwelling unit and sleeping unit separations need not exceed 1/2 hour (IBC 708.3). Two conditions matter on the set:
- the reduction applies to the unprotected construction types (IIB, IIIB, VB); a Type IIIA or VA building keeps the 1-hour separation;
- the sprinkler system has to be NFPA 13 throughout; an NFPA 13R system does not qualify for this reduction.
Floors between units
Floor and ceiling assemblies separating dwelling units are horizontal assemblies under Section 711 (Section 420.3). They are rated at 1 hour, with the same 1/2-hour reduction for Types IIB, IIIB and VB buildings sprinklered throughout under Section 903.3.1.1 (Section 711.2.4.3).
Continuity
A fire partition's rating is only as good as its continuity. Section 708 requires the partition to extend from the top of the floor below to the underside of the floor or roof above, or to a rated ceiling that is part of a horizontal assembly, with the supporting construction rated to match. On a wood-frame building, this is where the attic and the floor cavity details decide whether the separation holds: draftstopping, fireblocking and the rating of the structure that supports the partition all show up in the details.
Corridors
Corridor walls in an R-2 building are rated by Table 1020.2 of the IBC (2021 numbering). For Group R with an occupant load greater than 10 served by the corridor, a corridor in a building without a sprinkler system is not permitted to be unrated; in a building sprinklered throughout under Section 903.3.1.1 or 903.3.1.2 (NFPA 13 or 13R), the corridor rating is 1/2 hour (Table 1020.2, 2021 IBC as adopted by Illinois, UpCodes). In practice almost every new multifamily building is sprinklered, so most apartment corridors are 1/2-hour fire partitions.
Corridor doors, the walls above the corridor ceiling and the openings into units follow from that rating: door assemblies in a rated corridor need the matching rating and closers, and penetrations through the corridor walls need listed protection.
Shafts and exit stairs
Vertical openings that connect floors are enclosed with fire barriers (Section 707) and horizontal assemblies (Section 711):
| Element | Rating | Source |
|---|---|---|
| Shaft enclosure connecting four stories or more | 2 hours | IBC 713.4 |
| Shaft enclosure connecting fewer than four stories | 1 hour | IBC 713.4 |
| Interior exit stairway connecting four stories or more | 2 hours | IBC 1023.2 |
| Interior exit stairway connecting fewer than four stories | 1 hour | IBC 1023.2 |
For both, the count of stories includes basements and excludes mezzanines. Section 1023.2 lists exceptions, including stairways built under Section 510.2, the podium provision, which is why the stair enclosure in a podium building's lower stories needs its own reading.
The 2-hour threshold at four stories is the one that catches multifamily projects. A five-story wood-frame building over a podium has trash chutes, elevator hoistways, mechanical shafts and exit stairs that connect four or more stories, and each needs 2-hour enclosures detailed through the wood floors.
Penetrations and joints
A rated assembly is broken every time a pipe, duct, cable or recessed fixture passes through it. Section 714 governs penetrations and Section 715 governs joints and voids. On a multifamily building the counts are large: every unit has plumbing, electrical and mechanical penetrations through its separations, and every floor line is a joint at the exterior wall.
The drawings handle these in two ways. Tested systems are named in a penetration and joint schedule, often on a sheet of their own, keyed to the conditions on the plans and details. And the specifications require the installer to submit the listed systems for each condition. A plan checker reads both; a contractor installs from both.
How the separations show on the set
A multifamily set shows its fire separations in four places, and the four have to agree.
| Where | What it shows |
|---|---|
| Code analysis sheet | construction type, sprinkler standard, the rating of each element under the applicable table and section |
| Fire separation plans | each level with rated walls, rated floors, shafts and stairs shown by a line type or hatch keyed to the rating |
| Wall and floor types | each assembly with its rating, the listing or tested design behind it, and its sound rating |
| Details | head-of-wall, floor line, corridor, shaft and stair conditions, and the penetration and joint systems |
The fire separation plans are often where plan check starts. A reviewer traces the dwelling unit separations, the corridor walls and the shaft enclosures on each level, then checks that each line type matches a wall type with the right rating, and that the details close each assembly at its edges.
Where sets go wrong
Corrections on multifamily fire separations tend to fall into a short list:
- A reduction claimed without its condition. A 1/2-hour unit separation on a Type VA building, or with an NFPA 13R system.
- Rated lines that stop. A corridor wall drawn rated on the plan and shown unrated in the section above the ceiling.
- Shafts rated by habit. A 1-hour chase in a building where the shaft connects four stories.
- Assemblies without a listing. A wall type with a rating and no tested design behind it.
- Penetrations left to the field. No schedule of systems, so the installer and the inspector settle it on site.
Each of these is a drawing problem first, and each is caught by reading the four places above together before the set goes out.
Construction type sets the starting point
Every rating above sits inside the building's construction type, which the code analysis fixes first. The common multifamily types each start from a different place:
- Type VA (protected wood frame) needs 1-hour structural elements and keeps the 1-hour unit separations, since the 1/2-hour reduction does not apply to it.
- Type VB (unprotected wood frame) has no required rating for the structure itself, and with NFPA 13 throughout its unit separations can drop to 1/2 hour; its height and area limits are the lowest.
- Type IIIA (protected, with fire-retardant-treated wood exterior walls) and Type VA are the two common choices for the wood floors of a podium building, and both keep 1-hour unit separations.
- Type IA (noncombustible, rated concrete or steel) is the usual podium below a 510.2 horizontal separation.
The choice is made in schematic design for height and area reasons, and every wall type and detail in CDs follows from it. Changing type after DD changes most of the fire separation plans.
Sound ratings ride on the same assemblies
The walls and floors that separate units for fire also separate them for sound, and the building code sets sound transmission requirements for those same assemblies in Chapter 12. Because one wall type answers both, the wall and floor types on a multifamily set list the fire rating and the sound rating together, each with its tested design. Choosing the assembly once, in design development, saves changing both later.
Where the studio fits
TECTO Studio draws multifamily sets in your Revit model with the fire separation plans, wall and floor types and details built from the same model, so the rated lines, the types and the details agree. The construction documents page describes the work, and the DD checklist shows where these decisions belong.
Sources
- IBC 2024, Section 708.3, fire partitions, fire-resistance rating (ICC)
- IBC 2021, Section 1020.2 and Table 1020.2, corridor construction (ICC), and the Illinois adoption on UpCodes
- IBC 2021, Section 1023.2, interior exit stairway construction (ICC)
- IBC Sections 420.2, 420.3, 711.2.4.3, 713.4, 714 and 715, 2021 and 2024 editions
- California Building Standards Commission: codes