Clearances for Wood Fire Doors

NFPA 80’s safety inspections of fire door assemblies, specifically swinging fire doors with builders hardware, have brought to light the issue of clearances between the door leaves and the frames and between the meeting stiles of paired doors.  Clearances in excess of the dimensions specified in Section Clearances in NFPA 80 are one of the most often cited deficiencies for swinging fire doors with builders hardware.

Remedial work to restore the clearances to within the specified dimensions includes shimming of the hinges (a technique used to make minor adjustments to the position of the door(s) in the door frame), replacing the door leaves with correctly sized (larger) doors, removing and reinstalling the entire existing door assembly, and replacing the existing door assembly with an entirely new assembly (e.g., door frame, door(s), and hardware).  Each of the remedial options progressively requires more time, labor, materials, disruption of the existing space around the door assembly, and cost.

In the case of hollow metal/steel fire doors and door frames, paragraph (see insert) allows an over-tolerance of 1/16-in. (1.59 mm) to the clearance dimension of 1/8-in. (3.18 mm), which is intended to accommodate the expansion of the super-heated hollow metal doors under fire conditions.  Even with the allowed over-tolerance a large percentage of hollow metal fire door assemblies are cited for excessive clearance dimensions that require corrective action work.  It should be noted that hollow metal fire doors are required to be installed in labeled hollow metal door frames or in channel iron door frames (the latter type of door frame is not labeled, but constructed of structural steel)—this is an important difference between hollow metal fire doors and wood fire doors to bear in mind as you read this article.

On the surface, the decision to allow an extra 1/16-in. (1.59 mm) of clearance between the door frame and the edges (and meeting stiles of pairs) of wood doors, high pressure decorative laminate faced (HPDL) doors, and stile and rail wood doors might appear to be a straightforward decision with few, if any, consequences.  Upon closer review, however, the issue of allowing an extra 1/16-in. (1.59) clearance identifies several areas of concern that need to be addressed before an allowance for a larger clearance dimension can be considered.

Unlike hollow metal fire doors, wood fire doors (which for the purposes of this article include flush wood, high pressure decorative laminate (HPDL), and stile and rail wood doors) are permitted to be installed in labeled door frames that are constructed from the following materials: hollow metal (aka, steel), pressed steel (not the same as hollow metal), wood, composite (veneer-wrapped high-density materials), and aluminum.  While each of these types of labeled door frames share common elements (e.g., door stops, door rabbets, and trim/casing of some form), there are notable differences in their design and construction that raise the concern as to how the larger clearance between the door(s) and frame might affect the performance of the door assembly under fire conditions.  For example, some of the door frames have integral door stops that are 1/2-in. (12.7 mm) in height, which is 1/8-in. (3.18 mm) less than the height of door stops of typical hollow metal door frames.  Some of these door frames have applied stops that fit into rabbets or groves—these stops range from 1/2-in. (12.7 mm) to 5/8-in. (15.88 mm) in height.  The standard fire door tests (e.g., NFPA 252, UL 10B, UL 10C, and UBC 7-2 1997) require test units to be installed with clearances between the doors and frames no greater than 1/8-in. (3.18 mm), which means that the current listings of these types of door frames do not permit larger clearance dimensions.

The height of the door stop on a labeled door frame might affect the maximum rating of the door assembly.  Generally, the door(s) close against the door stop of the frame, which prevents the door(s) from swinging in more than one direction.  The door stops of the frame overlap the top and vertical edges of the doors, forming a barrier that slows the passage of smoke, gases, and flames to the non-fire side of the door assembly.  Therefore, the height and configuration of the door stop portion of the labeled door frames is critical to the performance of the fire door assembly.  Its importance becomes more evident when the clearance dimension between the door and frame is larger than 1/8-in. (3.18 mm).

For instance, when the clearance between the door and frame is 1/8-in. (3.18 mm) and door frames have 5/8-in. (15.88 mm) high door stops, the door stops overlap the edges of the door by approximately 3/8-in. (9.53 mm) when the stiles have the standard 3-degree bevel and by approximately 1/2-in. (12.7 mm) at the top edge and at the vertical edges of unbeveled doors.  (See Figure 1.)  In either case, an additional 1/16-in. clearance reduces the overlap of the door stop by nearly 20 percent at the vertical edges when the doors are beveled. (See Figure 2.)  When the allowance for additional clearance is considered for frames with door stops that are only 1/2-in. (12.7 mm) high, the overlap of the door stop is reduced by nearly 33 percent—a significant reduction in overlap that might cause such a door assembly to fail prematurely under fire conditions.

Figure 1: Typical Hollow Metal Door Frame with Mineral Core Wood Door (with Beveled Lock Stile)

Figure 2: Same Door Frame with 3/16-in. Clearance—Notice the Position of the Corner of the Door in Relation to the Door Stop.

Another area of concern is the construction of specific models of wood doors.  While there are industry standards such as the Window and Door Manufacturers Association, WDMA I.S. 1A-13 Standard for Interior Architectural Wood Flush Doors and WDMA I.S. 6A-13 Standard for Interior Architectural Stile and Rail Doors that establish industry standards for performance (duty-level), construction, and aesthetics of wood fire doors, there is a great deal of variance in the internal components (e.g., materials, dimensions, composition, and construction) used in the construction of wood fire doors—even in a single manufacturer’s product line; especially, when you compare the construction of 1/3-hour rated doors to 3/4-, 1-, and 1-1/2-hour rated doors.

Consider the construction of 1/3-hour (20 minute) labeled wood doors.  1/3-hour doors might be constructed with one of the following core materials: particle board (PC), stave lumber core (SLC), structural composite lumber (SCL), or agrifiber (AF).  Depending on the selected core material, the doors might have internal stiles (the vertical members) that are constructed from solid wood or high density materials (e.g., Super Stile, Super Stile II) that are laminated to wood edge bands (the portion of the stile that is visible at the vertical edges of the doors).  Likewise, the internal top and bottom rails of wood doors vary in material and construction.  The actual dimensions of the internal components vary with the composition of the door, even in doors that are produced by the same manufacturer.  To compound the issue, most wood door manufacturers offer optional construction elements such as 5-in. (127 mm) high top and bottom rails, and in some cases vertical stiles. (Note: These larger stiles and rails are intended to accommodate the application of certain hardware devices and can be used to eliminate the need for using through-bolts to attach surface-mounted hardware to the doors.)  In addition, 1/3-hour wood doors that are rated for positive pressure applications are available in models that do not require integral (Category-A) or supplemental intumescent seals as well as models that do require some form of intumescent seal.

The internal construction of wood fire doors that are rated for 3/4-hour, 1-hour, and 1-1/2-hour varies greatly depending on the core material and the level of fire protection-rating needed for a specific application.  Like the 1/3-hour rated wood doors, the higher rated doors are constructed in accordance with the above mentioned WDMA standards, but the composition of the internal components vary between manufacturers and even within the same manufacturer’s product line depending on the level of fire protection-rating and the composition of the core.

Other Dynamics to be Factored into the Equation

Other dynamics that affect the clearance dimensions include the manufacturing tolerances for doors and frames, installation of the door frames in the field, and the skills and competencies of the door and hardware installers.  Most people are not aware that door openings in stock/standard hollow metal door frames are slightly oversized in width to accommodate square-edged hollow metal doors.  The head member of the door frame is typically minimally over-sized in length, which affects the actual width dimension of the installed door frame.  When hollow metal door frames (sidelight door frames) are assembled from blank stock (aka, stick built), the actual width dimension of the door opening the frames is subject to the accuracy of the persons assembling and welding the frames—the fabricators need to pay close attention to the dimensions of the door openings as they cut, notch, and weld the frames.  (Note: Door frames, other than stock/standard hollow metal frames, are designed with door openings that are not over-sized in width.)

Generally, wood door suppliers submit detailed engineering sheets (aka, machining sheets) for each order of wood fire doors that they place with the door manufacturers.  More experienced door suppliers tend to order the doors sized 3/16-in. (4.76 mm) less than the nominal door opening width dimension (e.g., the actual width of a door for a nominal 36-in. (914.4 mm) wide door opening is ordered as 35-13/16-in. (909.64 mm), which should result in clearance dimensions within NFPA 80’s current requirements; provided the door frame is properly installed.  Many door suppliers order the wood doors sized a full 1/4-in. (6.35 mm) less than the nominal door opening width, which requires the door frame to be installed nearly perfect in order for the clearances to comply with NFPA 80.  Frequently, the gap between meeting stiles of paired doors is much greater than 1/8-in. (3.18 mm) for the same reasons.

Installation of the door frames is the most important dynamic of all.  When the door frames are not properly squared, leveled, plumbed, and aligned, during the installation process, the door leaves will not fit the door frames correctly.  Bearing in mind how critical the installation of door frames is for fire door assemblies, consider when and how they are installed on a typical project.  Door frames that are set in masonry walls are erected before the walls are constructed—usually these frames are installed by the mason contractors very early in the project schedule.  Frames installed in stud partitions (wood or metal) are frequently set in place as the partitions are constructed—these frames are installed by the rough carpenters or mechanics.  Door frames that are designed to be installed after the wall board and other materials are in place (e.g., slip-on drywall frames, pressed-steel frames, aluminum frames, and wood/composite frames) might be installed by the drywall contractor or by the installers of the doors and hardware. The latter installers, generally, are able to more accurately install the door frames, which significantly improves the installations of door assemblies.

Call for Industry Action

I think it is a fair statement to say that the prevailing opinion in the architectural/commercial door industry is that wood fire doors should be allowed to have the same over-tolerance clearance dimension as hollow metal fire door assemblies.  As pointed out at the beginning of this article, the issue appears to be straightforward.  However, as you have learned the issue is not that simple.  I have been unable to discover any substantive documentation that addresses the installation of wood fire doors that were tested by nationally recognized testing laboratories (NTRLs) with a maximum clearance of 3/16-in. (4.76 mm).  Most likely, the absence of this data is due to the fact that the actual fire door test standards do not allow test assemblies with clearances over 1/8-in. (3.18 mm).  Consequently, very few, if any, fire door tests with over-sized clearances without supplemental equipment/devices to mitigate the larger clearances have been conducted.  Another reason for the apparent lack of existing data is that the majority of fire door testing is proprietary to the respective manufacturers and not is not available for public review, which is entirely understandable.

It is my opinion that the industry needs to work together to complete this research and answer the question, once and for all time, of how a clearance dimension of 3/16-in. (4.76 mm) affects the performance of wood fire doors.  Door and hardware suppliers, fire and egress door assembly inspectors, door and frame manufacturers, NTRLs, industry associations (e.g., AWI, BHMA, DHI, HMMA, SDI, and WDMA), contractors/installers, and all other interested parties need to pool their resources to accomplish this task.

On behalf of the NFPA technical committee (FDW-AAA), the committee responsible for the development of NFPA 80 and NFPA 105, I am researching this issue and gathering support for conducting generic testing of fire door assemblies with wood doors that are installed with the over-sized clearance dimensions—no gasketing or other mitigating hardware appliances/devices will be used in these tests.  Several model test assemblies (complete with door frame, door(s), and hardware) are needed for this project.  In addition, financial support is needed to fund the administrative, engineering, fire door testing, evaluation reporting, and related expenses of this project.  Just how much funding will be needed is unknown at this time as the total costs will be predicated on the actual fire door testing that is conducted.  In some cases, formal engineering evaluations by the NTRLs that are based on existing fire door tests might yield useful data, which could reduce the number of actual fire door tests that need to be performed.  It is not unrealistic to expect these expenses to approach or exceed $100,000 for this research project.

Regardless of the outcome of this research project, I think that the door opening industry and ultimately the general public at large will benefit from this project.  If the fire door testing results show that the increased clearance dimension does not compromise the integrity of fire door assemblies, more existing fire door assemblies will be in compliance with NFPA 80 requirements for periodic safety inspections—at least, in regards to the clearance requirements.  Conversely, if the fire door test results show that the increased clearance dimension does compromise the integrity of fire door assemblies, then NFPA 80’s current clearance requirements will have been verified and other changes in the industry might be necessary to improve the installation and maintenance of fire door assemblies.  Either way, the questions regarding the maximum allowable clearance for fire door assemblies will have been answered.

Please forward this article to persons who are in positions to make decisions to support this important industry research.  For more information regarding this topic and the research project, contact me through my LinkedIn account or email me directly.

Thank you for taking the time to read this article.

PS:  You might be interested in joining the new LinkedIn discussion group: Fire Door Safety.  Enter “Fire Door Safety” in the search field at the top of the page and choose the “group” filter.

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