Please note that this article aims to offer general information only and is not a replacement for expert guidance from a contractor or builder concerning your specific project. Further, building code standards are subject to change, and any references to such requirements in the article should be verified with local professionals.
Why Do You Need Deflection Clips?
Through the use of slots, deflection clips or slide clips allow for isolating vertical movement in building structures. This is particularly useful in exterior curtain wall or “bypass” framing to allow for flooring or roofing to deflect without transferring loads to walls.
Exterior Curtain Walls (Bypass Framing):
In many cases, exterior curtain walls are not integral to the primary building structure, but they usually depend on the primary structural framing for support. It may be advantageous in many scenarios to isolate the vertical movement of the primary building structure from the curtain walls. Many of the clips designed for bypass framing restrict lateral movement, but allow vertical building movement.
The primary structure can be expected to move up and down due to live-load occupancy as it is loaded and unloaded. If the exterior curtain wall collects compressive load or load from gravity that it is not designed to withstand, it can result in deformation or other failures of the stud framing.
An additional concern related to gravity, concrete structures typically undergo shrink and creep over time, and there may be additional movement due to settling in the foundation. These might also cause improper loading without proper allotment for relative movement between the curtain wall system and the primary structure.
One final example of why managing vertical movement is important for the success of your project can be found in the seasonal or temporary displacement caused by expanding and contracting of different material types due to temperature difference. Cladding materials installed on curtain wall systems are often a significant expense to the overall construction project and directly affect the look and feel of the finished structure. Isolating these materials from the primary structure can prevent cracking or damage that might result in cosmetic defects or weather intrusion.
Image: Curtain Wall Bypass Framing
How to Install Deflection Clips:
Depending on your specific application, clip geometry, and structural requirements, there are several different installation methods for deflection clips and slip clips. Hardware connections to the building can be made with framing screws, powder-actuated fasteners or drill-in concrete anchors. Call to inquire if you have specific hardware needs for framing. In some cases, one side of a deflection clip can be directly welded to the primary building structure. On the exterior side of the clip that enables vertical movement of the curtain wall system, clips are installed with specialized fasteners such as the proprietary ClarkDietrich FastClip screw that has been specifically designed to provide friction-free deflection. In many cases, proprietary screws are included in your purchase of clips, but they are also available for individual purchase in both FastClip Screw 55 piece bags and FastClip Screw 80 piece bags.
See the images below for several of the styles of deflection clips that we have for sale in our online store:
Image: Installation of Flat Tail Side Clip (FTSC) available in multiple configurations
Image: Installation of Fastclip Slide Clip - HD
Image: Installation of a Fixed Universal Slip Clip (FUS) available in multiple configurations
Image: Installation of Fast Top Clip (FTC) available in multiple configurations
Image: Installation of a FastClip Slide Clip (FCSC) available in multiple configurations
Image: Installation of Extended FastClip (FCEC) for large standoff conditions available in multiple configurations
Drift FastClip Slide Clips provide for both vertical and lateral movement and are available in multiple configurations
Why Do You Need Drift Clips such as Head-of-Wall Clips?
Head-of-wall clips are used in deflection conditions for in-fill curtain wall assemblies and/or interior non load-bearing partitions to provide for both vertical (deflection) and lateral (drift) movement. Similar to deflection clips, head of wall clips also enable vertical deflection, but in head-of-wall clips this goal is sometimes achieved by encapsulating the end of the stud in a sliding channel rather than additional bolts sliding in slots. These clips are used in place of, or in combination with, deflection track. The clips can be attached to the underside of structural members, concrete decks, or flooring assemblies. Studs must be cut less than full height to enable vertical movement.
Interior (Infill) Curtain Walls:
Another standard curtain wall framing practice is infill framing. This is typified by studs running from the top deck of one floor to the underside of the floor above. Curtain walls can serve many potential purposes, from purely aesthetic to highly functional. For example, curtain walls can be tailored to suit various styles and can accommodate curves, angles, and irregular shapes. Moreover, these walls can be covered with various materials and finishes for even greater customization. From a functional view, adding infill curtain walls to your project can improve sound isolation, provide opportunities for natural lighting to penetrate building interiors, and improve efficiency by creating insulated thermal zones.
From a purely structural perspective, the purpose of these walls is based solely on interior building organization and function. There are no structural load bearing requirements. Due to live-load deflection that varies between the various floors of the building and potential seismic loads in high seismic areas it is often advantageous to allow for both vertical and lateral movement relative to the primary structure.
Image: Interior Infill Curtain Wall
How to Install Drift Clips:
For drift clips in interior applications such as head-of-wall clips, attachment to the primary structure can be made with 1/4-14 screws, or concrete anchors and should be driven through the slotted holes and positioned in the center of the slot to allow building drift. To ensure slip, back-out the fasteners about 1/2 turn. The "C" shaped end of the clip is slid inside of the structural stud and is not fastened, which allows for vertical deflection.
Installation of drift clips for exterior applications is similar to installation of deflection clips (see last example in previous section), but can also make use of 2-piece systems such as the ClarkDietrich Drift Rail and Drift Rail Clip system shown below.
Image: Head-of-Wall Clip Used to Fasten Curtain Wall Stud available in multiple configurations
Image: Two-piece Drift Rail and Drift Rail Clip system available in multiple configurations
Heavy Wind and Seismic Concerns:
It is not possible to completely mitigate risk of damage in the case of an earthquake or heavy winds, but various protection strategies absorb the energy of an earthquake or winds and reduce damage to buildings and structures. Different size buildings often employ vastly different strategies to protect from damage. For example, a simple residential project might make use of shear walls and multiple hold down connections to create a highly rigid structure resistant to horizontal racking. By contrast, a skyscraper might make use of sophisticated foundation dampeners or vertically configured counterbalances to counteract the swaying of the tall structure.
Seismic forces attack and reveal the weakest link of the building system. Failure of structural beams or columns could result in building collapse. Lateral loads from both seismic events and heavy wind can result in torsional displacement throughout a building structure. Planned failure points such as highly ductile bracing and strategic frame connections allow for damage to the building to be isolated while preserving the integrity of the overall structure. This strategy prevents the building from immediately falling down so that occupants have the time needed to safely evacuate.
Learn more about deflection and drift clips on Clark Dietrich's website.