Understanding roof glazing specifications

20 May 2021

pure glass flat rooflight specified by Exact

Each and every piece of architectural glass is meticulously designed and specified by our team of specialists, to ensure it meets the necessary performance and safety standards.

Of particular importance is the glass specification featured within roof glazing due to the inherent issues surrounding glass installed at height. Read on to find out more about glass specifications and the importance of working with glazing specialists for your project.

What factors determine glass specification?

During the Initial Project Consultation, we will discuss the full details and requirements of the architectural glazing required. The key to achieving the optimum glass specification for roof glazing is understanding the location and size of the installation. Every project requires meticulous planning to ensure the safety, security and durability of the installation.

What is heat-soaked or strengthened glass?

Glass that has been heat-soaked or strengthened undergoes a strengthening process during manufacturing to expose nickel sulphide (NiS) inclusions in tempered glass.

During this process, glass is exposed to extreme temperatures in the region of 290oC for approximately 2 hours within a heat-soaking oven. Panes that contain nickel sulphide shatter, therefore reducing the likelihood of breakage in situ.

Following the strengthening, the risk of spontaneous breakage for heat-soaked glass drops dramatically from 1m2 in every 10,000m2 to just 1m2 in every 1 million m2.

What is toughened glass?

Toughened glass, which meets the definition of ‘safety glass’, is also created via a heating and cooling process, with additional compressive stress. To meet the definition of safety glass, additional safety features are required to make it less likely to break or less likely to cause harm upon breaking. Toughened glass tends to break into ‘dice’ – or small rounded fragments, which are less likely to cause injury. Risks still remain that the dice clump together, creating a large section of glass.

Specifying glass for roof glazing is critical to achieving a safe installation and ongoing performance. The associated risks of breakage can be further reduced by specifying heat-soaked toughened glass.

What is heat-soak toughened glass?

As the name suggests, this is glass that has been through both heat-soaking and toughening processes. Following the toughening process, the glass is then heat-soaked to eliminate any sheets of glass that are liable to spontaneous breakage, due to the nickel sulphide inclusions. During the treatment process, there is a risk of breakage which can increase manufacturing times, however, the glass units which are produced via the heat-soaked toughened method should have greater resilience and longevity.

What is laminated glass?

Laminated glass refers to two or more sheets of glass that are bonded together with a strengthening interlayer. The interlayer is specifically designed to bond the glass sheets together should breakage occur. Without lamination, a spontaneous breakage of toughed glass has the ability to cause significant damage or injury.

Whilst British Standards recommend this for glazing above 5m or above water (such as a swimming pool), our commitment to achieve the safest, optimum performance for all of our bespoke roof glazing means that we always specify a laminated inner pane. In the unlikely event of breakage, broken glass is held in place by the interlayer and doesn’t fall.

Pure glass flat roof light by Exact

What are warm edge spacer bars?

Used to frame and separate the double or triple glazed unit, we specify warm edge spacer bars as standard within our roof glazing units. Made of a thermally non-conductive material, rather than a standard spacer bar, warm edge spacer bars reduce the risk of condensation and improve energy efficiency.

Preventing condensation and heat transfer

Comfort, safety and thermal efficiency are important factors in specifying glass for roof glazing. Our double-glazed units are filled with argon and hermetically sealed to provide a significantly more effective barrier against heat transfer, keeping the temperature variation in your home to a minimum and reducing any draughts.

Adding a low E coating provides enhanced protection against heat loss, with centre pane ‘U’ values of up to 1.1 Wm2/oK. 

What is SN70/35 solar control glass?

In years gone by, large glass installations were associated with poor thermal performance making the home too cold during winter and too hot during the summer months. Advances in glass technology mean modern glass installations specified with SN70/35 solar control glass provide excellent thermal and solar performance, as well as high light transmission.

What is self-cleaning glass?

When specifying glass for a roof installation, we always recommend a self-cleaning coating. The unique coating works at a microscopic level to continually break down organic dirt. Rather than rain/water running down the glazing in the usual rivulets, the coating causes the water to spread over the glass into a sheet – wiping away the dirt as it runs off. Glass remains cleaner year-round, while the coating also allows the glass to dry more quickly to create a streak-free view.

Find out more about self-cleaning glass  

The importance of frame design for roof glazing

In specifying roof glazing, the glass and frame are designed as one to achieve optimum performance. Our range of roof glazing includes Pure Glass Roof Lantern, Flat Roof Light, Aluminium Roof Lantern and Pure Glass Bespoke.

As well as a thermally broken frame, the Pure Glass Roof Lantern and Pure Glass Flat Rooflight also feature a drip detail. This drip detail ensures the unit is completely watertight as soon as the installation is complete onto the upstand.

Without a frame and drip detail specified, water will easily trackback on the underside of the glass and cause leaks, as the seal between upstand and glazing weathers over time.

Pure Glass roof Lantern Frame by Exact

Arrange a consultation to initiate your project with Exact

We aim to start our projects with an Initial Project Consultation to discuss your project in detail and understand the vision. During your consultation, we’ll discuss your specific needs and explain our full range of glazing systems as well as our approach and expertise. This ensures we can provide you with the products, service and expertise you need.

Book your Initial Project Consultation






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