Balancing views, solar control & daylighting

John Godwin of Vena looks at the need to achieve a tricky balance when considering architectural glazing.

When it comes to specifying the glazing for a project, all too often the need to achieve good views out can override the importance of solar control and regulating glare. In addition, the longer term maintenance requirements that secondary shading devices require can be overlooked, as well as the additional costs of their installation.

While maintaining a visual link with the outside is an important consideration, the daylighting of the internal space is equally important. Focusing less on the views out and more on how the internal space is protected from the glare and contrast in lighting levels from bright sun light helps to create a more user friendly environment, promoting greater productivity and wellbeing.

Selection of the right solar coating on a glass to achieve desired lighting levels and control heat gain is part of the consideration when selecting glazing, however this also need to be coupled with the external appearance required and most suitable shading method to best meet a project’s individual requirements.

Direct sunlight through clear solar control glass creates intense areas of light which are distracting and often result in blinds being used. These in turn can result in artificial lighting being turned on to overcome the loss of the natural light.

To avoid this, light diffusing interlayers or finishes can be incorporated in the glazing or, if better diffusion is required, a three-dimensional interlayer can be incorporated within the cavity. This form of capillary insert, when hit with direct

sunlight, bounces the light within the small tubes inside, resulting in the light that enters the space travelling in many different directions and creating an evenly distributed natural light.

There are a number of different ways in which the important visual link to the outside can be achieved, such as using external blinds or brise soleil, as well as internal blinds that can be operated to suit changing daylight. These provide low heat gain in summer months by blocking out the sun and in winter allowing more low level light into the space which in turn helps to reduce the heating loads. A TSET (g value) as low as 8 per cent can be achieved for a 60 degree sun angle, with the view out being constantly visible.

This type of system, while having a more solid appearance during the day, can come alive at night as artificial lights are switched on, revealing the interior space.

Metal louvres are another device that can be incorporated within insulated glass units and, depending on the design of the louvre, can offer basic shading as well as enhanced performance features such as re-directing light up onto the ceiling, or blocking views in a particular direction where privacy is an important factor or where planning restrictions insist views in a particular direction are prevented.

Louvres of various types are available to go into glazing units in both moveable and fixed configurations and, as with all the various shading solutions, the ease and accessibility for maintenance should be considered carefully alongside other aspects such as performance.

SOLAR CONTROL

Diffusing light to create an evenly and naturally lit space using Okawood integral timber blinds

Direct sunlight through clear solar control glass creates intense areas of light which are distracting

Fixed louvres, for both facades and roof glazing, avoid the maintenance issue and, by carrying out a solar assessment specific to a building’s layout and orientation early on, the louvre type can be selected to offer the best shading with minimal direct light coming into the space.

For spaces where the consistency of the lighting level is more critical this can be achieved by using a rooflight louvre that completely blocks all direct sunlight from the south while allowing the naturally diffused northern light into the space.

Where the appearance of metal louvres is not visually appropriate, you can use timber louvres. Being less reflective they are ideal in high-density areas, and the light that is emitted into the building is softer and more natural.

By considering early on in the design of a project what the key requirements that the glazing has to meet are, a finished project of high architectural merit and user comfort can be created, tailored to suit planner, designer and end users needs in a way that is easily maintained, and which will look and function well for many years to come.

John Godwin is director at Vena