Adrian Lowenstein, P.E., MBA’s Post

Almost all European façade systems do not provide for bonding on the construction site. Bonding on the façade is problematic both from the point of view of application technology and from the side of product quality control according to the European norm for structural glazing. Therefore, these systems are more expensive than conventional ones. The use of toggled systems allows you to use a standard system and visually get a similar look to the structural façade. In Europe, these similar systems are used quite often and have been for more than 25 years. Systems of design and calculation of IGU for toggled façade systems are quite well developed and tested by many years of experience. For example this is the third generation of Schueco's toggled system. Therefore, it is not a concept for us. By the way, a façade with cold-bent IGU windows is currently being installed in this system. This is the most complex variant of toggled systems both from the calculation side and from the technological side. But this is a real concept.

The only thing Im not a fan of is the outter lite is unsupported, causing the secondary seal to be under constant shear. Or the dead load of the outter lite is taken up by the weather seal which will cause bulging and continue transferring load down the wall.

Just to add to this: The reason we like to do this in Europe is because it removes the structural element being completed on site. If the glass is just bonded back to the barwork on site then you are relying on good workmanship. Building sites are also dusty. If the barwork is not prepared properly or the silicone is not applied to the correct bite size. Then you have a risk of glass falling from the building. Any reasonable option to mitigate this should be taken. Hence the toggles.

The only thing Im not a fan of is the outter lite is unsupported, causing the secondary seal to be under constant shear. Or the dead load of the outter lite is taken up by the weather seal which will cause bulging and continue transferring load down the wall.

Europe do structural calculation on IGU secondary sealant and IGU manufacturer take on and are paid for that additional responsibility. In US not.

I recall a 3 1/2” thick glass unit in a US system with a spacer toggle by a Company called Hordis Brothers… we did a few in a ribbon application back in the 80’s but it never really caught on….

The toggle system is very obsolete and the main problem is that under wind load (mostly the negative pressure) the IGU resistance is limited to the one of the inner glass panel. So, unless the inner glass is sufficient enought to structurally perform I would never recommend the toggle solution.

Very interesting topic, which I discussed in the past few days in breaks with other façade industry professionals during Challenging Glass Conference in a visit at Octatube. By what I heard, US regulations don't fully trust the secondary sealant strength of the IGUs. Sometimes municipalities in Europe are also skeptical about that and demand mechanical fixation systems all the way to the outer layers. Elevated temperature and extended load durations indeed pose a risk depending on the project, but it's gaining trust as it has been working pretty well for a while in many projects. I am particularly fond of the toggles or butterflies as it gives more transparency overall, but of course it's a project dependant decision. Cheers!

Agreed that the outer lite at least half of the glass should be supported by the glazing block for deadload, as most people have noticed in the detail. When we think about toggle glazing, we should keep in mind the roles of the primary and secondary sealants. The primary seal (at the spacer) acts as a barrier to keep air or gases in and to stop moisture vapours from entering the cavity. The secondary seal is the structural component that maintains the integrity of the IGU. The question should be does the IGU still maintain structural integrity and whether there are any decreases in the performance values on the building envelope. It is about what is best suited for the building where it is being used. A cool toggle system is WICONA from Germany https://www.youtube.com/watch?v=dwZvEJAo8Fs

This is a good option without a pressure plate and cover cap. However, maintaining the position of the channel within the DGU can be challenging. If not done correctly, it can lead to issues such as air leakage and a wobbling sound from the glass due to improper toggle fixing.