In this issue:
The purpose of the newsletter is to provide technical points of interest, and fabrication/installation issues that may be helpful to you in the future, either from a problem avoidance or solution perspective or just from a general interest point of view.
In this first issue, given the unexpectedly sunny weather, we thought we would kick off by tackling the issue of solar glare as a result of glazed roofs. We have invited one of our Glass Suppliers, to provide information from a new installation perspective, and another of our film suppliers to provide information of what can be done post installation.
Ask the Expert – John Pearson of Dual Seal Glass on Sun Glare
Glare is the difficulty of seeing in the presence of bright light, as occurs in direct sunlight passing through glazing. It can cause discomfort, resulting in an instinctive desire to look away from the bright light, perhaps when reading a book or newspaper, or difficulty in seeing an object, such as a computer screen. The solution is to restrict the amount of light entering the window by using a solar control glass, which reflects more visible light than clear glass and reduces glare inside the building to an acceptable level.
Insulating glass units for glazing typically include coatings that control the solar heat gain, by reducing the g value, and, in turn minimise glare by limiting the visible light transmission. For instance, typical roof glazing would have a light transmission of between 25% and 55%, combined with a g-value of between 15% and 30%. The final choice depending on the area of glazing and orientation of the building i.e. if it is South facing, or a glazed roof.
In residential conservatories or orangeries, the roof glazing may be specified from any point in the range of transmission data, being tinted or coated and in some cases both, depending on the desired performance and appearance from both inside and outside the building. Glass may be specified in either green, blue or grey body tinted, or Saint Gobain ST 150 combined with a low-e coating on the other pane, or one of the most recently developed coated products, Guardian SunGuard SNX 50/23. The vertical glass in residential conservatories often being a low-e coating and clear glass.
Reducing Solar Glare FAQ
How can glare be reduced in existing or older buildings? Many older office blocks are having to be adapted to cope with the requirements of modern technology and building regulations. A common problem which has to be solved, experienced by many companies, is when glare from the sun dazzles staff working at computers. To alleviate the problem in many cases a solar control film can be fitted, particularly to south-facing windows, which is a far more cost effective solution then replacing glazing in its entirety.
What are Solar control films? These are of particular use in combating severe solar heat gain and glare problems. They also alleviate the discomfort caused by glaring reflections off computers screens, assisting in compliance with the Workplace (Health, Safety and Welfare) Regulations.
What about roof glazing and conservatories? The most popular products in respect of roof glazing are the Reflective Silver type films, both the internal and the external grades. These typically come with a guarantee of 5 years and the lifespan would be dependent on the exact environment around the film. We would expect an internal film to perform for approximately 10 years and the external 5 to 7 years.
These films are of particular use where there is a need to control light levels for atmospheric effect, e.g. in museums, and for UV control in areas used for certain light sensitive manufacturing processes.
These films also offer glare reduction for staff comfort, whilst still making use of daylight as a source of illumination.
How do they work? Reflective films can cut out slightly better as the heat and glare is reflected away prior to it even getting to the glass.
When installed to internal glass faces, the light passes through the glass
hitting approximately ¾ of the suns energy from coming through the glass into a building. Applying this film externally works the film on the internal face and it is then reflected back through it and back out into the atmosphere.
Are there any precautions that should be taken? Please note, the film choice must be chosen carefully in order to avoid glass breakage due to thermal stress.
What is thermal stress? Thermally induced stress within a pane of glass results from a temperature differential between two areas of the pane. For instance, in hot weather, the centre of the glass warms up faster than the edge, because the edge is within the glazing rebate and shaded from direct solar radiation. Assuming the area of glass within the frame is insignificant compared with that exposed to solar radiation, as the centre of the pane expands due to the increase in temperature, the edge will be forced to expand by a similar amount inducing a tensile stress. This problem is common in retail environments, where stores adhere promotional information and films to the surface of glass (offer stickers, manifestations, corporate decals etc). Solar radiation is therefore more pronounced in these areas as they absorb the suns energy instead of allowing it to pass through the glass.
How can thermal stress fractures be avoided? For new glazing our recommendation is that the glass is, at the very least toughened during its production, which makes its characteristics more resilient to thermal stress? Ideally, the glass should be Heat Soak Toughened which is a more thorough manufacturing process that encourages the glass to break in the factory environment instead of on site.
How about if the glass has already been installed? Thermal stress fractures can be combatted using films with low solar gain absorption, external applications to cut the heat out at source and checking the glass compatibility with a specified product, with the glass manufacturer prior to the film application.
Are you having trouble with solar glare? Then Click Here for you solution!