Effect of floor slab movement on system selection

Glazing and cladding systems need to be designed to allow for building movements without compromising the performance or safety of the system. Therefore, the effects of building movements on the glazing system selection needs to be considered at the early planning stage of a project to ensure that the correct glazing system is specified.

It is necessary to maintain a minimum clearance between the edge of a glass unit and the framework that it is installed into in order to avoid breakage of the glass. This edge clearance typically needs to accommodate the following movements: – slab deflection, sway of the building under wind load, long term settlement / shrinkage of concrete and thermal movements.

The image on the right shows the effect that slab defection has on glazing / cladding elements that are connected to it causing them to drop and adopt a rhomboid shape.

Different systems are capable of accommodating different movements for example a 60mm curtain wall system is able to tolerate greater structural movements that a 50mm system. Unitised facades can typically accept greater movements than curtain walling system whereas structurally glazed curtain walling can take very low levels of building movement.

The second image shows the effect where the building movements and the glazing system are not aligned. The glass is in danger of hitting the framework of the system which in turn increases the risk of glass unit fracture.

Detailed consideration is required in the planning stages as not only do the building movements have an effect on the system selection but also the configuration of the glazing. For example, a tall unit in portrait can take far less movement than a wide unit in landscape.  Therefore, a combination of storey height narrow panes of glass in portrait will need a very stiff structure in order to make it work.

If the desired glazing system selection and configuration planning is not aligned with the building structure at an early stage in the project, it can cause unforeseen delays and costs while it is aligned at a later stage.