June 9, 2020

Structural Glass Facades vs Slim Façade Systems

Written by Carly Coren

Options for incorporating a glass façade in a commercial project

Often commercial buildings make an impact with a striking façade, when you are looking to create entire walls of glass as part of a design there are various options at your disposal. In most cases, when designing a wall of glass you want the glass to be the prominent feature of the façade. This means minimising the framing and using the largest glass panes feasible.

There are many façade systems available on the market, each varies greatly in terms of frame size, material and design. Structural glass can be used as a modern alternative to a traditional façade system and comes with fewer restrictions as well as a more minimal design. IQ has developed bespoke fixing details for structural glass to allow for entire elevations of glass with completely hidden frames and fixing details. This is achieved by a technique whereby the glass is stepped over each floor, creating a seamless finish.

But when it comes to specifying your glass elevation what is going to be the best solution for you and your project design? Here we explore the most identifiable differences between a structural glass façade and a glass elevation made with a slim framed façade system.

Framing

The key design element of structural glass is that there is no frame. The glass units are fixed to the building structure using channels or angles that are designed to be hidden, regardless of the design. This means that with IQ’s expertise and experience, a completely frameless aesthetic is achieved.

For the most minimal façade system opt for an aluminium frame. The most minimal façade system has framing sightlines of 35mm on the face. With a façade system, you will also have to consider the size of the ‘box’ behind the glass which gives it its strength. These box sections vary in depth depending on the height of the elevation and the wind load of the project.

As an example, the slim façade system from IQ has a frame of only 35mm however the transom depth depends on the weight of the glass unit. For glass units of 250kg or less the transoms is 70-155mm deep. Heavy Duty Transoms are used for glass units of up to 400kg and are 130-155mm deep.

Glass Sizes

The maximum glass size you can achieve with a façade system is determined by the weight of the glass. This means that if triple glazing is used, or thicker laminated glass units need to be integrated, the maximum size of the glass you can use will be reduced.

Structural glass is not governed by maximum glass size or weight restrictions. On commercial buildings using a structural glass façade, the only restriction on glass size will be dependent on budget and site access.

The biggest glass panes made in the UK are 6m x 3.2m. Use panes of glass this size as part of your façade design for a striking finish. This structural glass façade in London (Wigmore Street) used frameless structural glass panes of nearly 6m tall, to create the glass wall of the double-height lobby. The glass wall didn’t have to be dissected with any horizontal framing or mullions and the result is a clear and clean-cut glazed elevation. 

If you want to use glass units bigger than 6m x 3.2m to create your glass façade, the glass must be sourced from overseas. This will add cost and may increase the lead time of the glass but can be a great way to create high impact glass elevations.

When using a façade system to have a maximum glass weight of up to 250kg as standard. This can increase to 400kg using deeper or ‘heavy-duty’ transoms. Using a typical glass specification of a double glazed unit with 6mm toughened glass, you could get a maximum size of 8m2 for a standard transom depth or 12m2 for a deeper transom, up to 155mm.

Glass Specification

When considering structural glass there is great freedom with glass specification. You do not have to create glass units to a certain weight restriction or depth, you are free to include entirely bespoke glass units into the façade with little consequence to the design details.

This means that you can use multiple laminated layers of glass, triple glazing, electrical glass and decorative glass all within one pane of glazing if desired. Most projects wouldn’t require this but the freedom gained by removing the parameters of a façade system allows designers to be a lot more creative with the design process.

A façade system will have a set maximum and minimum thickness for your glass units. This range is broad to allow for most typical glass finishes or types. Flat coatings like low-e coatings, solar control coatings and tinted glasses are all possible. You could even integrate a technical glazing solution like Heated Glass or Privacy Glass for a fully responsive glass façade design.

Decorative finishes can be achieved by using a printed or coloured interlayer, or by applying a screen-printed pattern on the surface of the glass, to create a manifestation or logo. Laminated glass increases the weight of the glass unit, this could reduce the size of the glass units permittable within your elevation and is something to be considered at the specification stage of your project.

Shaped or Unusual Designs

Structural glass has many design benefits but when it comes to bespoke or unusual glass façade designs it really outshines the alternative options. As there are no framing systems involved with the creation of a structural glass façade you can engineer a structural glass wall to any specification. This could include simple alterations like angled or shaped facades to more complex 3D structures.

Some façade systems will allow some variation on the design for a more bespoke finish, this may include the ability to create shaped or angled glass installations. It is much easier to create bespoke designs using a structural glass installation as there are no limitations.

This may be of special importance on a listed building. Structural glass can be easily detailed and designed to be in keeping with all the requirements from English Heritage or the local authority.

Highline 

The Highline modern glass facade system combines large, fixed elements for structural glazing with ultra-slim profiles, making it ideal for large, uninterrupted glazing installations.  When specifying an aluminium and glass façade system, it is important to discuss the performance values of the system with your chosen glazier to ensure project requirements are met, and any limitations of the system. The Highline aluminium and glass façade system utilises high performance, thermally broken framing profiles and structural glazing to allow fully glazed facade designs to be realised. Flexibility in design is key to allow the system to be specified to achieve certain values, or achieve a certain aesthetic to blend in to the build of stand out to become a design feature.

Cost

As there is so much choice available for a structural glass installation, costs can vary dramatically. If you are using very large glass units, glass that has to be sourced from overseas, specialist electrical glass finishes or many layers of glass the cost of the glass package will increase. However, when looking at a structural glass facade you should normally look to budget for at least £1000 per m2.

The costs of a slim façade system will change depending on the system you choose. As an example, the Slim Façade System from IQ starts at £750 per m2 and structural glazing is approx. £1000 per m2.

If you are interested in comparing a structural glass façade to a slim framed façade package for your project, contact the experts at IQ Glass who will be happy to answer any questions. You can call us on 01494 722 880 or email hello@iqglassuk.com.