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TECHNICAL PAPERS
Fire Rated Head-of-Wall
Deflection Joints
Adventures in Solving a Non Existent Problem Duane Jonlin, Technical Architect, NBBJ Seattle Introduction Fire-Rated Head-of-Wall Deflection Joints Adventures in Solving a Non-Existent Problem Duane Jonlin, Technical Architect, NBBJ Design/Seattle This paper considers the selection of head-of-wall joint systems for fire-rated partitions intended to accommodate structural deflection. Applicable regulations and test standards are reviewed, and the extent of floor system deflection is discussed. The paper concludes with comparisons of the available systems and recommendations for their selection and detailing. .  Floor
systems deflect under live load. If the floor above a full-height
partition deflects sufficiently, the wall and the smoke/fire seal
at the top could be damaged. If the floor below the partition deflects,
a gap could open at the top allowing passage of smoke and fire.
With this concern in mind, our vigilant code writing community has introduced standards in the past few years to guard against this threat. Under the 1997 UBC, the joint between the top of a partition and the floor structure above it must be sealed with an assembly that meets stringent testing standards. The Rationale For Use of Deflection Joints Where does the code require these joints? Section 706 (Fire-Resistive Joint Systems) of the 1997 UBC requires that deflection joints between fire-resistive floor and wall systems be fire tested in accordance with UBC Standard 7-1. ICBO also publishes an "Acceptance Criteria" document for testing of joint systems. This document, ICBO-AC30, recognizes UL Standard 2079 as an acceptable alternate testing standard. UL 2079 is very similar to UBC Standard 7-1, but allows small-scale testing in place of full-height wall testing. Most manufacturers use the UL 2079 standard. One manufacturer has sent out literature lately claiming to have the only code-compliant system available on the market, because they are the only ones whose testing conforms to UBC Standard 7-1. However, the use of alternative systems is allowed by UBC Section 105, and therefore assemblies tested under either UBC Standard 7-1 or UL Standard 2079 are acceptable. How are head-of-wall joints tested? Under UL 2079, the lower portion of the joint assembly is cycled up and down through its full range of motion 500 times, after which the joint is checked to see if it's still intact. It is then cycled to its most wide-open position and moved into a fire-testing furnace. After an hour of the fire test under positive pressure, the temperature on the furnace side of the wall will have reached 1,700 degrees F. Meanwhile, the temperature sensors on the cool side have to remain below about 320 degrees and the wall can't leak any hot smoke or gasses. While the wall is still hot, they blast the joint with a fire hose stream to see if the impact or temperature shock of the pressurized water will damage it. Any excess temperature rise, hot gas leakage or hose stream water penetration will cause the assembly to fail the test. How much do floor systems deflect?  The
typical standard for structural deflection design in floor assemblies
is L/360. Thus, a 30-foot beam is designed to deflect up to one
inch under its design load. In a 30 X 30-foot structural bay, the
main beams could deflect an inch and the intermediate purlins could
deflect an additional inch, for a 2-inch total in the center of
the bay. Keep in mind, however, that a floor system is almost never
loaded to full design capacity, the beams are rarely designed to
their maximum allowable deflection, and various safety factors and
structural interactions serve to limit deflection even further.
Curiously, our structural engineers seem unanimous in advising us
to provide for 1û2-inch or 3û4-inch deflection for almost any structural
system or bay size. Perhaps the most significant aspect of this test is not specified by the test standard. The actual distance that these head-of-wall joints are designed to deflect is left up to one's engineering judgement. Architects typically call upon structural engineers to specify that distance. The movement capabilities of tested assemblies in the UL Directory range from 1/8-inch up to 3 inches in each direction. As mentioned below, there is almost no record of interior partition damage due to deflection, except in severe earthquakes. It seems likely that the calculated extent of floor deflection is greatly overstated in most cases. Varying Deflection Terminology Manufacturers typically list the total (fully compressed to fully extended) movement capability of their joint systems, whereas structural engineers state requirements in terms of the simple deflection of each floor system separately. If your engineer requires 1û2-inch deflection capability for each floor, you need to choose a system that has a 1-inch total movement capability. The UL Directory lists the "Nominal Joint Width" for each deflection joint plus its "Movement Capabilities" as a percentage of the joint width. Thus, a 3û4-inch nominal joint width with 33% movement capability in both compression and extension would allow 1û4-inch movement each direction, or 1û2-inch total. What Happens If You Don't Provide Enough Deflection Capacity? If you were to look back in time to the early 1980's, you might have a hard time remembering how architects solved this deflection problem. This would be because the profession typically either ignored the issue entirely or utilized some homemade solution. During the following decade, more awareness about the issue developed, and many architects began using nested track assemblies or V-grooved "deflection track" for their head-of-wall joints. At the same time, concern was growing about the best practices for sealing all kinds of joints and penetrations in fire barriers. It had been noted, appropriately enough, that just stuffing some mineral wool around a pipe where it passed through a floor slab did not create a permanent barrier to the spread of fires. In addition, the 1994 Northridge earthquake spurred a wave of reforms for working more effectively with seismic and other building movements. Earlier this year, I began a review of this problem in order to select a design standard that could economically and effectively seal rated head-of-wall joints. Using the 1û2-inch minimum deflection standard provided by my engineer, I found just a handful of rated assemblies that would qualify. However, a contractor had been lobbying a client of mine to approve one of the elastomeric spray fire sealants on the market that had only 3/8-inch movement capacity. In response, I began investigating what would happen if the assembly did not accommodate sufficient deflection. I first called the Northwest Wall and Ceiling Bureau (http://www.nwcb.org/ncbright.html). In case you haven't met them, the people at the NWWCB are a great resource for plaster and drywall questions. After thinking it over for a while, they couldn't remember even a single incidence of a partition failure due to deflection. This observation came from two specialists who have investigated every imaginable type of interior wall failure. Thinking there must be some mistake, I talked to Al Andrew, the layout chief for Vertecs Company, a major wall finish contractor. He said that he had once seen some minor crushing at the top edge of some drywall in California, but that was it. Next was Anita Washko of Wiss, Janney, Elstner Associates, a forensic engineering firm that investigates building failures nationwide. After conferring with other experts at WJE, she reported back that there were no such failures showing up in any of their databases. Unwilling to give up, I posted the question in three different on-line discussion groups. My only response was from Jason Fell, Technical Director of the Drywall Information Trust Fund in California, who replied that he had heard of some failures of the V-groove type of deflection tracks during the Northridge earthquake but had not seen bowing or other deformations of partitions due to deflection. (Later, I did uncover one instance of deflection damage locally. In that case, a tall lightweight partition had been built tight to the long-span structure above in a conference facility. The metal studs took on the whole structural load and bowed out noticeably.) If Deflection Is Not a Problem, Why Bother? The answer to my earlier question "What happens when you don't provide enough deflection capacity?" seems to be "Generally, nothing." I called Bob Anderson, a principal and senior structural engineer with Skilling Ward Magnusen Barkshire, to get an explanation. "Bob," I said, "you keep telling us that we have to accommodate a half-inch of deflection, but even the most knowledgeable experts in the region have never seen any deflection damage to interior partitions. Partitions erected thirty years ago with no deflection control at all are still completely intact. What is going on?" (Finally, I thought, I've got him cornered.) "Metal stud partitions have a certain amount of 'give' in them, Duane," he answered. "There is generally a little gap between the stud and the track, and the connections are rather soft. This will allow a modest amount of deflection to take place without loading up the studs. If deflection progresses beyond that point, the studs will carry the load down to the floor below. Since these loads tend to be applied axially, even light gauge studs will perform quite well, and the gypsum board screwed to each side will constrain them from bowing or twisting." "So how much deflection do we have to accommodate now?" I asked. "Sorry, Duane. You still have to accommodate the full half inch," he replied, "but maybe your partition assembly itself absorbs some of that movement." Three Categories of Head-of-Wall Joint Assemblies: Mechanical, Sealant & Membrane Systems The various fire-rated head-of-wall joint systems can be divided into three categories: mechanical, sealant bead and sprayed membrane. (For this article, only metal stud partitions with drywall faces are considered, but most of these systems also offer variations for masonry partitions as well.) Mechanical  The
"mechanical" assemblies include some familiar brand names such as
Fire Trak, Slip Track and Metal-Lite. Each of these systems has
a head assembly fixed to the structure above that allows the main
wall assembly to slide up and down within it. Deflection movements
are accommodated by allowing one component to slide past another.
The head assembly includes an apron or valance made of drywall or
metal angles, and the decking flutes above are sealed with fire-resistant
material. These systems offer movement capability from 1û2-inch
up to as much as three inches in each direction, and are generally
the most expensive options. Sealant Bead  The
second category of assemblies accommodates deflection by stretching
and compressing a bead of fire sealant. With these systems, and
there are dozens, a thick bead of resilient fire sealant is applied
between the top of the drywall and the decking above. The allowable
movement is typically in the range of 1û4-inch in each direction
(1/2-inch total). Where the wall runs perpendicular to the decking
ribs, these systems typically require the top edge of the drywall
to be "castle cut" to the profile of the metal decking above, or
else they are tested for compression force only and not extension.
The "castle cut" is an expensive and time-consuming drywall detail
that should be avoided where possible. Note that many of the "sealant bead" assemblies rely upon a seal with the top cut edge of drywall. It would seem that any movement in extension would pull a layer of gypsum dust off the top of the panel and leave a gap. Another problem is that, without a bond-breaker membrane along the side, the sealant could bond to the adjacent top track, greatly limiting its actual movement capability. Sprayed Elastomeric Membrane  The
third category, elastomeric sprayed membrane systems, includes products
by Hilti Construction Products, Specified Technologies, Rectorseal,
3-M and others. They are typically spray-applied in a layer 1/8-inch
thick, overlapping the drywall face below and the metal decking
above. Some of them have also been tested to adhere to structural
steel fireproofing such as Cafco 300 or Grace Monocoat MK-6. The
decking flutes above the wall are typically filled with compressed
mineral wool, which acts as a form for application of the sprayed
membrane. The products are so similar in application and tested
capabilities that they are virtually interchangeable. Each one,
however, must be installed according to the details specified in
its own UL tested assembly. These sprayed products are considerably less expensive and faster to install than the mechanical systems and have greater movement capability than the sealant systems. Earlier versions of these products allowed only 3/16 to 3/8 inch of compression or extension (3/8-inch to 3û4-inch total). However, Hilti, Rectorseal and Specified Technologies now have listed systems that will accommodate 1/2-inch of movement in each direction (1-inch total). This solves the deflection problem neatly, in that the most economical system type now meets all of our performance standards. Considering that deflection damage has never been much of a real-world problem in the first place, these products provide an ideal solution. Some of these UL approved systems are new enough that their most current version does not appear in the year 2000 UL Directory. UL now has its listed head-of-wall systems available online at http://www.ul.com/database/index.htm. Since these systems are continually being replaced and updated, this will make it easier to check on the latest approvals, and perhaps you can finally toss your ancient copy of the UL Directory. (Intertek Testing Services is the testing lab for Sliptrack Systems, but there does not seem to be any online listing of tested assemblies at Intertek.) CONCLUSIONS AND RECOMMENDATIONS Here, then, are my conclusions and recommendations. Some of the salespeople and manufacturer's I've spoken with may feel their products have been slighted. However, different conclusions could be warranted where the structural system, partition type or markets for labor and materials differ from the assumptions in this analysis. (This is also an appropriate moment to clarify that this recommendation is my opinion alone and does not necessarily represent the viewpoint of my employer or of the Puget Sound Chapter of CSI.) General Recommendation In general, specify and detail elastomeric spray-applied membrane systemsÖ Where a one-hour or two-hour rated head-of-wall deflection joint is required for an interior metal stud partition, specify one of the elastomeric spray-applied membrane systems that has been tested for 1û2-inch of movement each direction (one inch total movement). This currently includes: …
Recommendations for Special Conditions  Conflict
With Pipes and Conduit Close to Decking One condition under which
the mechanical joint systems should definitely not be allowed is
in tight construction situations where pipes, conduit or ductwork
need to run within a few inches of the decking above. Almost all
of the mechanical systems include an attached strip of drywall that
extends down several inches and must be free to slide up and down.
Therefore, the top of any pipe or conduit penetrating the wall would
have to be positioned several inches below the decking, wasting
valuable ceiling cavity space. Keep in mind that the fire-rated
pipe or duct penetration assembly itself often requires a flange
at the wall, which would further lower the penetration. Joints Exposed to View In most situations, the head-of-wall joint will be concealed in a ceiling cavity. In an exposed structure condition, consider the finished appearance of the joint and the method of filling the decking flutes above. This may warrant use of one of the more expensive mechanical configurations. Latex paint can be applied to some of the sprayed membrane systems, but will crack if the joint experiences movement. Deep Deflection Conditions If a fire-rated head-of-wall deflection joint is expected to experience substantially more than 1û2-inch of movement in each direction, as sometimes occurs in long span structures such as convention centers and warehouses, use one of the mechanical systems that has been tested for more extensive deflection. Fire Trak has systems tested to 3 inches of movement in each direction. (If you're expecting more than 3 inches of deflection, maybe you should find a new structural engineer.) "Secure Attachment" of Studs Sprayed elastomeric membrane assemblies typically allow the studs to slide up and down within the top track, so that the studs are held in line vertically only by the drywall panels on each side. Select a system that uses slotted top track or nested deflection track where one of the following conditions exists: (1) local code interpretations require "secure attachment" between the studs and the top track, (2) drywall is applied only to one side of a partition, or (3) imbalanced loads might be expected from heavy shelving or other wall-mounted elements. Check with the specifics of the test report from UL or Intertek for allowable configurations. The Specified Technologies (STI) elastomeric systems are tested both with and without a nested deflection track. SlipTrak slotted top track can be substituted for standard top track with most assemblies, and Firetrack offers an optional clip system to hold the studs in alignment. (On the other hand, I haven't yet heard of studs falling out of partitions that lack "secure attachment".) Where secure attachment is not provided, many systems call for a long-leg top track to provide a secure sleeve within which the stud slides. Support of Track Parallel To Decking Flutes  Where
the partition runs parallel to the flutes of the metal decking above,
provide adequate anchorage for the top track where one or both edges
of the track are unsupported. Some systems require 2-inch wide metal
straps or a continuous plate spanning between the decking ribs.
This condition has not been clearly addressed by all of the manufacturers.
Where only one side of the top track is secured to the decking rib,
my recommendation (not specifically tested by the manufacturers)
is to provide sections of J-furring or Z-furring in the decking
flute above to stabilize the unsupported side of the track. Remember
to fill the flute above with compressed mineral wool. Application Over Structural Steel Fireproofing Many of these elastomeric fireproofing membranes can be applied directly onto cementitious or fibrous sprayed fireproofing (such as Grace Monokote or Cafco 300) on the metal decking. Generally this requires the elastomeric sprayed fireproofing to overlap 2 inches onto the structural steel fireproofing instead of the 1û2-inch overlap that is required for application to metal decking. RECOMMENDATIONS FOR ALL PROJECTS Pre-Application Inspection For Sprayed Membrane Systems The specification should require that the entire system, including the compressed mineral wool in the decking flutes, be inspected just prior to the application of the spray. The studs and drywall should be checked to be sure that they have not been inadvertently fastened to the top track. (Installation crews, trying to do a good job, will often screw the studs to the track, or use temporary screws to hold the studs in place during drywall application and then forget to remove them.) The spray itself should be randomly tested after application to assure that the required thickness, usually 1/8-inch, has been applied. This 1/8-inch wet thickness will dry to approximately 1/16-inch. Use Only the Listed Brand-Name Components Each of the tested assemblies listed by UL or Intertek requires certain brand-name components, and substitutions are not generally allowed. A drywall contractor on one of our projects decided to save some money recently by fabricating his own track to match the proprietary system we specified. When the manufacturer of the specified track discovered this, a patent infringement lawsuit was promptly filed which became quite painful for the subcontractor. Details  Details
in the drawing set should illustrate conditions where the partition
runs parallel to the decking flutes, perpendicular to the decking
flutes, directly below beams, adjacent to beams, and perpendicular
to beams. They should be customized to show whether structural sprayed
fireproofing will be applied to beams and/or decking. Note that most of these systems are tested only for one or two typical conditions, leaving the architect or contractor to improvise at conditions for which no detail has been tested. Sloping rooflines, irregularly shaped penetrations, and radiused walls would each require special consideration and some extrapolation of the tested assembly performance. Another approach to detailing is to draw no details at all, but rather to rely upon a carefully-worded specification and the shop drawing review procedure. The risk taken with this approach is that the bidders, while perhaps legally obligated to provide the desired system, may not have been fully educated about the nature and extent of the details they are to provide. Specifications At my firm, the specifications for head-of-wall joint systems are contained in Section 07840, Firestopping, and Section 09100, Metal Support Systems. AIA Masterspec puts fire-rated, proprietary head of wall deflection assemblies in Sexction 09260 - Gypsum Board Assemblies. The firestopping section, which also specifies systems for rated wall penetrations and perimeter gaps, requires that the head-of-wall joint be a tested assembly which meets the fire rating requirements of the partition as well as the stated deflection requirements. The required compression and extension distance for the joints should be stated in this section, or else a specific reference should be made to another location in the contract documents. The section should specify a spray-applied elastomeric membrane system and also allow, at the contractor's option, one of the mechanical systems specified in the Metal Support Systems section. Product Evaluation Summary Consider the following product characteristics when evaluating proposed assemblies:
Although deflection at head-of-wall joints has rarely caused damage to partitions in practice, current building codes require that we provide tested assemblies at all fire rated wall heads. The available systems vary widely in cost and movement capabilities, and new or modified systems are constantly being introduced. Therefore, the specifier would be well advised to keep an open mind and write specifications to allow the least expensive solution that meets the stated criteria. (Just remember to state the criteria somewhere!) The answer to the earlier question "Why Bother?" is this; Properly installed, the head-of-wall joints will work in concert with rated penetrations, protected openings and slab edge assemblies to provide a complete fire containment envelope. Years from now, a potentially disastrous fire might be restricted to a minor one-room incident due to the diligent detailing of each of these fire-rated assemblies. Your efforts would be a small price to pay to protect the lives and wellbeing of your future building users. Appendix CSI Member Comments, Corrections and Experiences Please contribute your thoughts to this article mailto:djonlin@nbbj.com. Comments and experiences from CSI members would be most welcome and will be posted periodically. (We will remove your name if you'd like to remain anonymous.) Comments From the Manufacturers The product manufacturers mentioned in this article are invited to post responses so that they can offer their own viewpoints djonlin@nbbj.com. Further responses and dialogue will be included on this site as requested. Acknowledgements Editorial comments on earlier drafts of this report were generously provided by the following: Dace Campbell, AIA, Ed Storer, CSI, Anita Washko, CSI, Chris Dixon, CSI, Fred Novota, CSI, Don Breiner, AIA, John Jeffcot, CSI, Carroll Bryan, CSI, and Rob Lyons, CSI. The substance and style of this paper were greatly improved by their efforts. Chris Dixon, CSI, did the final editing, the layout design and conversion to HTML. The Technical Committee of the Puget Sound Chapter of CSI provides this research in the pursuit of technical excellence for its members. Reproduction of any portion of the text or images in this report for other than personal use is subject to permission of the author. Mechanical System Manufacturers
Assembly: UL Assembly listing number, except Intertek listing number for Sliptrack Systems Movement: First figure is allowable joint movement in one direction only. Second figure (in parentheses) is total movement for extension and compression. Assemblies are tested perpendicular to decking flute direction except where noted otherwise in Notes column. General Note: This listing is not comprehensive. "Sealant Bead" systems were omitted, as were most systems that were tested only for small movement capabilities. In addition, none of the concrete or masonry assemblies is listed or discussed here. Many more systems can be viewed online at www.ul.com/database/index.htm. |
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