NEVER TO BE SEEN


They cut through floors, walls and ceilings and are critical to managing structural building movement, but expansion joints can be challenging to integrate aesthetically in the overall building’s design. Andy Moul, European Director of Technical Services at Construction Specialties (CS) looks at how to ensure the expansion joint covers meet all functional requirements, while blending in with their surroundings.


An expansion joint, or movement joint, is essential to a building as it provides a structural gap between adjoining parts of a building that allows for safe and negligible relative movement of those parts, caused by temperature variations, ground settlement or other conditions. The joints are designed to accommodate building movement in a controlled manner, preventing damage to internal and external finishes. They go through the entire structure of the building from top- to-bottom and front-to-back of floors, interior walls, ceilings, exterior walls and roofs, and often become wider as the building gets higher.


Expansion joint covers (EJCs) are systems designed to provide a safe transition across an expansion joint opening and, when specified correctly, remain unaffected by the movement of the two surfaces either side of the joint.


RIGHT COVER, RIGHT APPLICATION Detailing and selecting EJCs for a project can be seen as a complex task. However, by taking a logical approach when considering various specification factors, the process is much simplified. The starting point is always the expansion or movement joint size and anticipated movement range. This relates to the width of the structural expansion gap under normal operating temperatures and will typically be established by the structural engineer. Minimum joint width is the narrowest (linear) gap that the joint is expected to close to, whilst maximum joint width is the widest gap the joint is expected to open to. Most expansion joint cover models are designed to suit a specific nominal joint width, with some models able to accommodate a range of joint widths.


A building’s anticipated movement range, which takes into account the impact of thermal movement, wind sway, lateral


shear or multi-directional movement on the structure, is crucial to EJC specification. The movement range can be presented as an overall movement, or as a percentage of the expansion joint width. For example, a 50mm nominal expansion joint with an anticipated expansion and contraction of 25mm could be expressed as 50mm +/-25mm; 50mm with a total movement of 50mm, or 50mm +/- 50%.


EJC selection will also be dependent upon what the building is used for and where within the building movement joints are located. For example, if the expansion joint is in a hospital or other type of building where hygiene and infection control are critical, then a smooth gasketed model may be the best option, as it will be flush fitting, wheel friendly and watertight. In a heavily-trafficked area where infection control is not an issue, such as light industrial, leisure or retail environments, an all-metal model that is hardwearing, easily assembled and tamper-proof may be the optimum solution. In all floor applications, the level of traffic and associated load requirements should always be considered. Finally, exterior wall and roof joints require specialist solutions, which are designed to withstand weathering and moisture ingress.


When it comes to aesthetics, it’s important to ensure that the selected EJC model is compatible with adjacent floor and wall finishes. Surface mounted products will generally work with most finish options, but their visible surface will be greater than in the case of recess mounted solutions. When minimal visual impact is important, some models allow for floor or wall finishes to be incorporated within them, to further reduce their exposed surface, or make them barely distinguishable from their surroundings.


Another benefit of recess mounted models is that they can be fitted flush with adjacent surfaces, which is often a


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