Joinery methods of Z-shaped girts can play a major role in the structural integrity of a building. There are several different joinery methods that can be used with advantages and disadvantages to all.
Sub-framing Z-girts are typically manufactured in limited lengths, such as 8’. This is necessary for installation purposes, as one person can typically install an 8’ girt alone. This can affect project plans, as most wall lengths are more than 8’ in length.
The ends of girts must be joined to create continuity along the wall. Some critical engineering metrics that need to be considered for these end conditions are:
- Structural stress and deformation analysis
- Attachment detail to the substrate
- Allowance for thermal expansion along the length of the girt
The most common wall configuration includes the horizontal installation of Z-shaped girts over vertical studs. The lateral joinery detail is required for structural calculations for the horizontal installation of Z-shaped girts over vertical studs. The following covers the most common joinery techniques for girts.
Lap Joints with Traditional Metal Z-Girts
Traditionally, steel Z-girts are made of relatively thin metal (i.e., 0.062”) with a high value of elasticity and stiffness. This allows them to easily lap and stitch together with a lap joint method. The basic lap joint consists of two overlapping members that are connected with screws or rivets.
This type of joinery is often used for metal z-girts due to the relatively thin material. The overlapping members create an interlocking connection that helps to distribute forces over a larger area than a single fastener could. This helps to reduce the risk of failure or buckling of the joint under high load-bearing applications.
When using metal z-girts, it is important to ensure that the lap joint is properly installed. Caution must be made not to fasten at all lap joints in order to allow for thermal expansion. It is also important to check that the overlapping pieces are properly aligned, as misalignment can lead to weak points in the joint.
Due to the increased relative thickness of composite or fiber-reinforced polymer (FRP) girts compared to steel girts, lap joint methods are not easily accomplished. When attempted with thicker girts, it creates out-of-plane offsets in the wall’s vertical plane.
Lap Joint Method for Steel Z-Girts
Butt Joints with Standard Fiber-Reinforced Polymer (FRP) Z-Girts
A butt joint is a type of joint that is formed when two pieces of material are joined together end-to-end with no overlap. Butt joints place each Z-girt end on half of a stud. This joinery method is unacceptable on a single stud for best practice considerations due to a minimum required margin space of 2.5 fastener diameters at the end of girt for FRP (0.25” fastener diameter x 2.5 required margin space + 0.25 “fastener + 0.1875” metal edge margin x 2 sides = minimum flange width of 2.125”).
To effectively use butt joints with FRP girts, double studs are needed at every FRP girt joint, leading to increased material and labor costs.
Butt Joint Method for Fiber-Reinforced Polymer (FRP) Z-Girts
Cantilever Joints with Standard Fiber-Reinforced Polymer (FRP) Z-Girts
The cantilever joinery method involves installing girts horizontally with a cantilever over the studs on both ends. While cantilevering Z-girts can provide a quick and easy joint, it does not provide the same level of security or integrity that other joinery methods provide. When cantilevering Z-girts, part of the girt is left unsupported, which can cause them to sag or become misaligned over time. This can cause problems with the structure’s overall integrity and can be dangerous if the girts are not properly secured.
While cantilevering Z-girts may be an option in certain situations, it is not best practice and should be avoided whenever possible.
For structural calculations, the maximum possible cantilever for the worst typical case should be used (15” for a 16” O.C. stud, etc.).
Cantilever Joint Method for FRP Z-Shaped Girt
Interlocking Joints with Composite Metal Hybrid (CMH™) Z-Girts
Interlocking joints with composite metal hybrid (CMH™) Z-girts is best practice for providing a reliable connection between two Z-girts. The GreenGirt® composite metal hybrid (CMH™) Z-shaped girt has an integral interlocking system that enables one end of a girt to connect into the adjacent girt. This type of joint eliminates the need for Z-girt ends to align and fasten at studs, which can reduce construction time and cost.
Interlocking joints are also structurally sound and provide greater strength compared to lap joints, butt joints, and cantilevers. The patented interlocking design of the GreenGirt® CMH™ Z-girt allows for ease of connection and installation of the Z-shaped girt while providing best practice structural integrity.
Importance of Joinery Methods
With different joinery methods possible using varying Z-shaped girt materials, it is important to consider real-life installation and application of the joint type. Proper joinery methods for Z-girts ensure that the structure is safe and secure and that the connection between the girts and the framing members is strong. If appropriate joinery methods are not used, the structural integrity of the building could be at risk of failure.
Advanced Architectural Products, creators of GreenGirt® CMH™ Z-girt sub-framing and SMARTci® systems, provide best practice solutions for building envelopes and continuous insulation systems. GreenGirt CMH provides a thermal break and structural mounting platform for applications creating an insulated building envelope with universal compatibility for any substrate, insulation, or cladding.
Specially designed to eliminate thermal gaps that other systems neglect, the SMARTci continuous insulation systems leverage the thermally insulated composite metal hybrid (CMH) GreenGirt CMH Z-girt technology for a best practice continuous insulation solution. Superior to steel structurally and thermally, GreenGirt provides the same loading capabilities of a steel Z-girt of equivalent depth. Additionally, GreenGirt is corrosion resistant.
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