The appeal of a glass wall, giving the full width and breadth of the outside world, is undeniable.  

Walls&Roofs spoke to Nick Wright of Nick Wright Consulting, president of the South African Glass Institute and Competent Person (glazing), to learn more about using glass in buildings and more specifically, about solar control glass. 

Why glass? 

Glass connects an interior space with its exterior environment. It also maintains a barrier against wind, rain, draughts, heat and cold. It basically keeps the unwanted outside! But it can also let the winter sun in and keep the warmth there. 

However, increasing temperatures due to climate change drive the need for managing heating and cooling through passive means.  

According to the South African government’s National Climate Change Information System (NCCIS), the country is plausibly committed to relatively large (compared to the global average) increases in near-surface temperatures, even under high-mitigation futures. 

The region can expect to experience an increase in mean, maximum and minimum temperatures.1 

Solar radiation 

Many people are familiar with the extreme temperature variations caused by the summer sun shining in through a large pane of glass or the chill from that same glass in the winter.  

The most obvious way to protect against summer solar radiation is by shading, including: 

• Shading devices. 
• Glass tinting and coating. 
• Fenestration types and design. 
• Size of the areas of glazing per elevation.

Insulation of the space can be increased, through a reduced U-value, by: 

• Double glazing. 
• Low E coatings. 
• Insulated frames including thermally broken, timber and PVCu. 
• Replacing window with insulation material, such as bricks – but really? Where’s the view? 

Energy-efficiency standards 

SANS 10400 XA describes controls for shading, insulation and air leaks to fenestration for glazed windows, doors and rooflights, and it has now been published as a second edition.  

To meet minimum standards, fit-for-purpose windows and doors are required, rather than the poorly performing products that are common on the market. Wright warns that inferior windows create excessive heat losses and gains, condensation, and hot and cold air leaks. 

Solar control glass 

Solar control glass is ordinary glass with coatings that reflect solar radiation, while allowing daylight in – essentially, less heat and maximum light. 

The cost of heating and cooling is also reduced when solar control glass is installed, delivering better energy efficiency to the building and lower ac bills. 

Specifying the correct glass and window is therefore key for a building’s fenestration. The biggest concern around solar control glass solutions, is the cost. 

Double glazing – the solution? 

Double glazing adds insulation, reducing heat transfer to a quarter of a single glass. It also reduces solar heat gain but keeps light transmission. Furthermore, it can help with sound control and reduces condensation. 

The question is, is it a cost-effective intervention?  

Wright’s calculations at 500m2 of fenestration, with the following assumptions: 

• An average summer temperature of 35oC outside aiming at 25oC inside,10 hours per day, 120 days per year. 
• An average winter temperature of 5oC outside, aiming at 20oC inside,12 hours per day, 80 days per year. 
• The coefficient of performance (COP) for air-conditioning = 2,5 for cooling and COP 1 for heating (electrical resistance heating). 
• Electricity = R4.13/kWhr, Benoni estimated July 2025. 
• Solar radiation is 500 watts/m2 for 120 days per year, for 10 hours per day. 

Efficiency vs payback 

Prices as of February 2025

Wright maintains that using solar control glass has its place, even in the face of climate change. He also says that considering the product’s long lifecycle, up to 30 years, it is not as costly as people may think. 

Specifying for success 

“Include a glass or facade specialist in the professional team, rather than relying on a glazier to complete the design alone,” says Wright.  

He further advises providing the following Bill of Quantity (BOQ) requirements for the glazing contractor: 

• Certification for the window system to be used to SANS 613 (to prevent air and water penetration) and meet SANS 10400N. 
• U value and SHGC certification to meet SANS 10400 XA. 
• Reference projects. 

The result: It is unlikely that new houses will be built without photovoltaic panels. Well, with energy-efficient glazing, you can also power your EV from your PV instead of your AC!  

In the face of climate change, is glass a viable option for buildings, both as a passive design measure or a cost-effective one? 

Reference: 

1. https://nccis.environment.gov.za/climate-services/climate-projections. Accessed 4 February 2025. 

For more information, please contact Nick Wright:  

Tel/WhatsApp: 082 808 1452 

Email: nicholasrw@mweb.co.za