18/05/2021
All insulated glass units that are used as part of a structurally glazed façade system must be manufactured with a silicone secondary sealant that conforms to EOTA ETAG 002 and EN 15434. Silicone sealants have excellent resistance to ultra-violet light, meaning the energy from sunlight is insufficient to significantly breakdown the silicone polymers.
Within domestic and commercial applications where the secondary sealant within an insulated glass unit is protected from ultra-violet light, such as conventional window systems and capped curtain wall systems, polysulphide and polyurethane secondary sealants are commonly seen.
Insulating Glazing | Components in IG Dual Seal System
Organic polymers are susceptible to ultra-violet degradation and therefore must not be used for structural glazing applications. The photographs below clearly show the degradation of organic sealants.
Insulated glazing units should be manufactured in accordance with BS EN 1279. If the insulated glazing unit is to be used in a structural glazing application, you should refer to EN 13022 which covers Insulated Glazing for Structural Glazing applications.
A silicone secondary sealant that meets the requirements of EOTA ETAG002 and EN 15434, is the prerequisite to achieve a safe and durable, structurally glazed facade.
Structural Sealant Glazing | Durability of Silicones
POLYURETHANE
POLYSULPHIDE
SILICONE
- Appearance- After 10 weeks UV exposure
- Consequence- Adhesion failure on glass
- UV resistance >40 years
- Temperature resistance up to 150 Degrees Celcius
- Oxidation resistance
- Fire resistance
- Only silicones approved for SG bonding and IG sealing in SG systems
On two-sided and four-sided structurally glazed façades, which can be supported or unsupported, the silicone secondary sealant also acts as a structural seal for the outer pane of glass as it bonds the outer glass to the inner pane of the insulated glass unit. If the glass is not supported, the structural sealant and the secondary sealant of the insulated glass unit’s must be calculated to accommodate the permanent static load resulting from the weight of the glass.
You can calculate the secondary sealant joint dimensions using Sika’s joint calculator for standard insulated glass units. The Sika joint calculator also takes into consideration the changes in barometric pressure within the insulated glass unit. In some situations, the change in barometric pressure can have a significant effect on the durability of the unit. This is particularly true for small insulated glass units and thicker glass panes, where the changes in barometric pressure have a greater impact on the secondary seal dimensions.
Insulating Glazing | Loads- Climatic Effects
Toggle Systems
In some structurally glazed designs, a toggle system is used. This entails the manufacture of insulated glass units with a U channel inserted into the secondary sealant. Once on site, the units are installed and then a toggle is rotated into place in the U channel mechanically fixing the inner glass to the façade frame. However, the outer pane of glass is still structural thanks to the silicone secondary seal of the unit. Specific calculations for the secondary sealant are required and are a part of the Sika Joint Calculator.
Glass Types
The insulated glass manufacturer will confirm the suitability of the units for the application and this includes the glass types.
Float glass does not require project-specific adhesion testing, but all other glass types will. Sika can support the insulated glass manufacturers with this.
The insulated glass manufacturer will carry out regular adhesion testing as part of their EN1279 factory production control system, and if the units are to be used in a structural glazed façade, it will be tested to EN 13022.
How do I access the online calculator?
The Joint calculator is easily accessible once registered through Sika Bonding Excellence Platform.
Sika can offer a one to one session on how to get the most out of the joint calculator and there are also online webinars that can be booked here, that will guide you through the process, with a useful question and answer session at the end.
To request an informative webinar on the Sika Bonding Excellence Platform please click the button below for further information.
As a Bonding Excellence Platinum Contractor, Sika will promote and support you in all your structural glazing projects.
Sika Here to Support You All the Way!
What if I have a non-standard application?
As part of Sika’s support for structurally glazed facades, any project-specific structural calculations can be done for you.
For non-standard applications, Sika have experienced Façade Structural Engineers who can provide you with expert help and advice.
For further information and advice please complete the below form to contact Andrew Hills | National Key Account Manager for Facades Fenestration Insulated Glass
On your request, Sika will send you a project information form, which we would ask you to return to us with all the relevant information required including glass data (especially the largest and smallest glass panel sizes, the glass configurations and wind loads, as previously mentioned). We also ask for drawing details for the project.
