What Are the Requirements For a Fire Door?

Fire doors are made to hinder fire and smoke from spreading in buildings – especially buildings with lots of traffic. This gives people time and more options to escape before smoke overwhelms them or fire surrounds them. This also gives the fire department time to get to the burning building and put out the fire, while protecting as much of the proprietors’ property as possible.

This article is meant to familiarize you with fire doors, how they are rated, and some basic requirements. We have some informative charts for you to look at, as well. Since we can’t cover everything in this article, since each state and each jurisdiction has a code that is somewhat different than the other and since laws change, we still ultimately refer you to the legal building codes in your area for specific information.


Fire doors are tested and rated by the Underwriters Laboratory (UL). You might be interested to know that all door parts are rated, as well, so that when parts are replaced they should be rated in accordance with the door and frame. Doors and parts are labeled according to how long they will hinder the spread of fire and smoke. Fire doors generally need to be self-closing, have a positive latch (a latch that catches firmly every time the door closes), and have limited undercuts, and gaps, vents and glazing. Fire labels may be made of steel, brass, aluminum, but also non-metallic material. These are usually placed on the hinge side of the door and frame. Doors that open into corridors may be required to meet smoke and draft ratings. These are labeled with an “S” placed under the hourly rating.

The door ratings are determined by the required wall ratings, which are determined by the location of the wall and local codes. The table below shows the relationship between the wall ratings and the door ratings. You will note that door ratings are required to be at least ¾ of the ratings of the wall around it, except that 1/3-hour rated doors can be used with 1-hour rated walls. One may use doors with higher ratings than the wall if all other standards are met. The rating you choose for a fire door will also depend on where in the building the door is placed. Please have a look at the chart below to give you an idea of which doors require what kind of rating.

 Fire Wall / Fire Barrier 4 HR 180 MIN Walls that divide a building into fire areas or separate establishments
 Fire Wall / Fire Barrier 3 HR 180 MIN Vertical walls connecting floors (stairwells, elevator shafts), boiler rooms, other high fire risk walls
 Fire Wall / Fire Barrier 2 HR 90 MIN Vertical walls connecting floors (stairwells, elevator shafts), boiler rooms, other high fire risk walls
 Fire Wall / Fire Barrier 1 1/2 90 MIN
 Fire Barrier 1 HR 60 MIN Walls between rooms
 Other Fire Barriers 1 HR 45 MIN Walls between rooms and corridors
 Fire Partitions 1 HR 20 MIN Corridor Walls, and wherever smoke and draft is a concern
 Fire Partitions 30 MIN 20 MIN Corridor Walls
 Other Fire Partitions 1 HR 45 MIN Non-Corridor Walls
 Other Fire Partitions 30 MIN 20 MIN Non-Corridor Walls
 Exterior Walls 3 HR 90 MIN Walls with the potential for severe fire exposure from the exterior of the building
 Exterior Walls 2 HR 90 MIN Walls with the potential for severe fire exposure from the exterior of the building
 Exterior Walls 1 HR 45 MIN An exterior wall that may be exposed to moderate fire from the exterior of the building
 Smoke Barriers 1 HR 20 MIN In corridors where smoke and draft control is necessary

It should be noted that 20-minute doors are not the same as 1/3-hour doors,
because 20-minute doors are not tested by standard fire test procedure, which includes the hose steam test.

Doors that are constructed to hinder heat from passing through to the other side. Ratings are set at no higher temperatures than 250o, 450o, or 650o during the first 30 minutes. These doors are generally used in stairwells to make it possible for people to get down the stairs of a burning building.

Frames used with masonry walls are used with 3 hr fire doors.
Frames used with drywalls and studs are used with 1 ½ hr fire doors.

The undercut is the distance between the bottom edge of the door and the top of the threshold. The NFPA-80 required this to be less than ¾ of an inch.

Fusible-link type vents max 24” by 24” in 1 ½ and ¾ hr doors are permitted on some fire doors. Vents are not permitted in 1/3 (20 min) doors or doors that are meant to keep smoke and drafts out, doors with lites, or doors with fire exit devices.


The rating of the door determines the windows (lites) used in the doors. The glass (glazing) is generally ceramic or it is wire glass. Of course, the window kit is also rated. Depending on local laws, windows may not be allowed in 3-hour rated doors. Below is a table that shows the limits of the windows in fire rated doors.


                                                Ceramic Glass
 Hourly Rating       Max Area                Exposed     Max Width     Max Height    Number of Lites
 180 minutes           100      12 inches      33 inches           One 
 90 minutes          1296      36 inches      54 inches         No limit
 60 minutes          1296      36 inches      54 inches         No limit
 20 and 45 minutes           1296      36 inches      54 inches         No limit
 20 Minutes w/o hose          2835      35 inches      81 inches         No limit
* Requires the use of a special bedding compound     
                                                 1/4 Inch Wire Glass
 Hourly Rating       Max Area                Exposed    Max Width    Max Height   Number of Lites
 90 minutes            100      12 inches       33 inches        No limit
 60 and 90 minutes*           2204      12 inches       46 inches          Four
 20 and 45 minutes*           2856      34 inches       84 inches        No limit
 20 and 45 minutes           1296      36 inches       54 inches        No limit
 20 minutes w/o hose           2994  35 13/16 inches    83 5/8 inches        No limit


 Label               Rating    Max Glazing
    A 180 minutes (3 hrs)       100 sq in
    B 90 minutes (1 1/2 hrs)       100 sq in
    C 45 minutes1296 sqare inch per lite
    D 90 minutes (1 1/2 hrs) Local Codes for exterior doors
    E 45 minutes Local Codes for exterior doors
 20 minutes 1296 sqare inch per lite
    S Smoke


The National Fire Protection Association (NFPA) requires that fire doors are inspected annually by certified inspectors and that records of those inspections are kept. NFPA 80 gives instructions on how to handle fire rated doors.


1. Fire doors must have an attached fire rating label.
2. Fire door frames must have either an attached or an embossed label.
3. Fire doors must be self-closing and self-latching.
4. Fire doors must be used with fire door hardware.
5. Fire doors must have steel bearing-type hinges.
6. If a fire door is held open, it must be equipped with a listed heat responsive device, fusible link or a smoke detection device.
7. Fire doors must be free of obstructions, such as door stops, chains and holdbacks, that prevent them from operating properly.
8. Double swinging doors that are not on an egress path shall have one overlapping astragal.
9. A coordinator or open-back strike should be used on doors that are on an egress path to ensure proper closing.
10. Fire doors with glass lights must have metal frames and glazing beads.
11. The glass must be labeled wire glass not less than 1/4″ thick or as permitted by the labeling agency.
12. Certain vents may be installed in 1¾“doors with a 1 ½ hour or a ¾ hour rating. Maximum vent size is 24” x 24”.
13. Vents may not be combined with glass lights, and are not permitted in doors with fire exit hardware or in stairwells.
14. Use the NFPA 80 as your instruction guide.

“We disclaim any and all liability in regard to the accuracy of the information contained in this article. Please consult a trained technician for your fire rating details and information. Please also note that different cities and counties have their own fire rating rules and requirements and that rules change. You should consult your local fire department for the latest information for your location”.



Automatic Door Doctors is a commercial door company, based in the Denver Metropolitan area, that repairs and installs automatic and manual doors.

Contact us