Glass Flooring Cost Design Factors
The thickness of glass used in a glass floor has a major bearing on the cost of the installation, and where cost determines the size and/or viability of a project it is always wise to look carefully at the factors determining the thickness of the glass in the flooring before drawing up the finished design. Thickness has two major effects on cost. Firstly raw material costs are affected and this relationship is not linear. For example a PVB bonded triple laminate 46mm thick is typically 2.2 to 2.6 times more expensive than a 24mm triple laminate. Secondly, the large increase in weight of the glass – 115Kg/M2 compared to 55Kg/M2 means that transportation and installation costs will also rise.
For a given laminate system, there are four main factors which affect the thickness of the glass to be used in any glass flooring installation.
The higher the loading the glass floor is required to take, the thicker and more robust the glass floor will need to be. For installations in the UK, a guideline to minimum loading specification can be found in BS 6399: Part 1: 1984. However, this must be treated with caution and designers must take into account the specific need of the end user. For example, it may well be that for a typical supermarket floor one might expect the requirement of 4.0 KN/ M2 distributed loading and a concentrated load of 3.6 KN as stated in Table 9 of the British Standard for shop floors to be sufficient. Perhaps to be on the safe side one might think to specify to 5.0 KN/M2 and 4.5KN to cover “corridors, hallways etc subject to loads greater than from crowds, such as wheeled vehicles and the like.” But, what actually is the concentrated load imposed by the little wheels of those big shelf restocking cages when fully loaded with cases of wine, or the point load of a 1.5Litre bottle of wine hitting the floor corner on?
The amount of support given to the glass-flooring panel also has an effect on the thickness of glass required. For example, to support a distributed loading of 5KN/M2 a typical PVB bonded triple laminated square panel measuring 1000mm x 1000mm supported by a ledge 25mm wide would need to be 32mm thick if supported on all four sides. However, it would need to be 46mm thick if only supported by two sides.
Type of Glass used
As a rule of thumb heat strengthened glass is approximately twice as “strong” as annealed or ordinary float glass, and fully toughened glass is roughly four to five times as strong.
It would seem to follow that using fully toughened glass would dramatically reduce the thickness of the glass to be used in glass flooring laminates and should be used throughout. In some cases it may be that this option is the best, but in general this is not the solution adapted.
Toughened and heat-strengthened glass does have an on-cost over float glass but in the case of fully toughened glass this is not the reason why it is not always used as standard in glass flooring.
The problem is that the tensile stresses inside toughened glass not only give the glass added strength, but also give an increased vulnerability to short sharp shocks particularly at exposed edges. This can result in an explosive release of stress producing the fracture characteristics of small, relatively harmless fragments sometimes referred to as dice. In a laminated system, having glass shatter into these less harmful fragments has little extra safety benefit over the larger sharper fragments resulting from the breakage of float or heat strengthened glass since all the fragments are held safely in place by the lamination.