Fire doors are required wherever a fire-rated wall, floor, or partition has an opening in it. If the wall is built to resist fire for a set period, any door punched through that wall must maintain the same level of protection. In practice, this means fire doors show up in stairwells, corridors, apartment entrances, garage connections, and anywhere a building is divided into separate fire compartments. The specific rating and location requirements come from building codes, primarily the International Building Code (IBC) in the United States and Approved Document B in the United Kingdom.
The Core Rule: Rated Walls Need Rated Doors
The simplest way to think about fire door requirements is this: a fire-rated wall is only as strong as its weakest point. Every opening in that wall, whether it’s a door, window, or duct, must be protected to a level that matches the wall’s rating. Fire doors are typically rated at three-quarters of the wall’s fire resistance. A door in a 2-hour rated wall needs a 1½-hour rating. A door in a 1-hour rated wall needs a ¾-hour (45-minute) rating. A door in a 4-hour rated wall needs a 3-hour rating.
There are two notable exceptions to the three-quarters rule. One-hour rated doors go into occupancy separation walls that are also rated at one hour. And 20-minute (⅓-hour) rated doors are used in certain corridor walls and smoke barriers with a half-hour rating. Those 20-minute doors are only permitted as hollow metal doors or wood doors, not every door type.
Stairwells and Exit Enclosures
Exit stairwells are one of the most common places you’ll find fire doors. The IBC splits the requirement based on how tall the stairwell is. Vertical exit enclosures that span four or more stories must have 2-hour fire-resistance-rated walls, which means the doors need a 1½-hour rating. Stairwells less than four stories require 1-hour rated walls and correspondingly rated doors.
These doors also face a temperature limit that other fire doors don’t. Doors in interior exit stairways and exit passageways must not allow the temperature on the non-fire side to rise more than 450°F above the surrounding air temperature after 30 minutes of fire exposure. This prevents the door from radiating enough heat to injure someone using the stairwell to escape.
Corridors and Hallways
Corridors that serve as exit access routes in commercial buildings, schools, hospitals, and multifamily housing often require fire-rated walls, which in turn require fire doors. The rating depends on the building’s occupancy type and whether the corridor connects to exit stairways or dead-ends.
Doors subdividing corridors that connect two or more exits typically need a 20-minute rating. The same 20-minute rating applies to doors that separate dead-end portions of a corridor from the rest of the hallway. These doors keep smoke and fire from cutting off escape routes before occupants can reach an exit. Doors forming part of the enclosure around a protected corridor leading to a stairway carry a higher requirement of 30 minutes.
Apartment and Flat Entrances
In multifamily residential buildings, the door between each individual unit and the common hallway or lobby is a fire door. This is one of the requirements most relevant to renters and homeowners in apartment buildings. These doors separate private living spaces from shared escape routes and must maintain the fire rating of the corridor wall they sit in, which is commonly one hour. That puts most apartment entrance doors at a ¾-hour (45-minute) rating.
Under UK regulations, all doors separating flats from common corridors and lobbies must be fire doorsets. The UK standard for these doors is E 30 Sa, meaning they must maintain integrity against fire for at least 30 minutes and include smoke seals. The same 30-minute standard applies to doors enclosing protected shafts forming stairways in buildings used for flats, offices, assembly, and recreation purposes.
Garage-to-House Connections
If your home has an attached garage, the door between the garage and the living space is required to be a fire door in most jurisdictions. UK Building Regulations explicitly require an E 30 Sa rated door (30 minutes of fire integrity with smoke seals) between a dwelling and its garage. US codes similarly require this separation because garages store vehicles, fuel, and other flammable materials that represent a significant ignition risk to the rest of the home.
Other Locations That Require Fire Doors
Beyond the most common locations, fire doors are mandated in several other situations:
- Fire walls and fire barriers. Walls that divide a large building into smaller fire areas, or that separate adjoining buildings, carry the highest ratings (up to 4 hours), requiring 3-hour rated doors.
- Incidental use areas. Rooms housing boilers, furnace rooms, storage rooms for hazardous materials, and similar spaces must have automatic-closing fire doors separating them from the rest of the building.
- Protected lobbies. Lobbies that provide a buffer zone before a stairway or evacuation shaft, including evacuation lift lobbies, require fire doors with at least a 30-minute rating.
- Exterior walls with fire exposure. Doors in exterior walls that face a neighboring building or property line close enough to present a moderate fire risk must carry a ¾-hour rating.
How Fire Door Ratings Work
Fire doors are rated in minutes or hours based on how long they can withstand a standardized fire test. In the US, the common ratings are 20 minutes, 45 minutes (¾ hour), 1 hour, 1½ hours, and 3 hours. Doors are tested under standards like NFPA 252 and UL 10C, which expose the door to controlled fire conditions and, in most cases, a hose stream that simulates the impact of firefighting water on a heated door.
The 20-minute rated doors used in corridor walls and smoke barriers are sometimes tested without the hose stream, depending on the specific wall type. Doors in fire partitions with a half-hour rating must pass the hose stream test. This distinction matters for specifying the right product, though it’s typically handled by architects and code officials rather than building occupants.
Self-Closing and Latching Requirements
A fire door that doesn’t close on its own during a fire is essentially useless. That’s why nearly all fire doors must be self-closing and self-latching. The door must be equipped with a closer that pulls it shut automatically, and the latch must engage without anyone turning a handle. If you’ve ever walked through a heavy door in a stairwell that swings shut behind you with noticeable force, that’s a fire door closer doing its job.
Doors that are normally held open for convenience, like those in busy corridors, must have automatic-closing devices connected to the building’s fire alarm system. When the alarm activates, magnetic or electromechanical hold-open devices release, and the closer pulls the door shut. Propping fire doors open with wedges or other objects defeats the entire purpose of the assembly and violates fire codes.
US vs. UK Requirements
The underlying principles are the same on both sides of the Atlantic, but the specific standards differ. In the US, the IBC and NFPA 80 govern where fire doors go and how they’re maintained. Ratings are expressed in hours and fractions of hours. In the UK, Approved Document B sets the requirements, and ratings are expressed as E (integrity) values in minutes, often with the Sa designation indicating smoke seals are required.
One notable UK-specific requirement: corridors connecting alternative exits in commercial and residential buildings must be subdivided by fire doors rated at E 20 Sa (20 minutes with smoke seals). Dead-end corridor sections carry the same 20-minute requirement. Doors in protected stairways and evacuation shafts require E 30 Sa across most building types, including offices, flats, and assembly buildings. The UK system places particular emphasis on smoke control, which is why the Sa smoke seal requirement appears so frequently.
How to Tell If a Door Is Fire Rated
Every fire door carries a permanent label, usually a small metal plate or sticker on the hinge edge of the door. This label identifies the manufacturer, the fire rating, and the testing standard the door was certified under. If the label is missing, painted over, or illegible, the door can no longer be verified as fire rated. Removing or obscuring a fire door label is a code violation. If you’re trying to determine whether an existing door in your building is fire rated, checking the hinge edge for this label is the fastest way to confirm.