How to design and specify Glass Roofs and Skylights

The definition of Daylighting is ‘lighting an indoor space with openings such as windows and skylights’.

Teams of experts from around the world have investigated a range of design factors, from indoor air quality and thermal comfort and daylighting, to acoustics, interior layout and views. Overwhelmingly, research clearly demonstrates that the design of an indoor space has a material impact on the health, well-being and productivity of its occupants. Evidence also suggests students with the most daylighting in their classrooms progressed 20% faster on math tests and 26% on reading tests in one year than those with the least. Similarly, Hershong Mahone’s also documented a link between daylight from skylights and improved Retail sales.

BS 8206-2:2008 Code of Practice for daylighting stipulates space with a mean daylight factor between 2% and 5% is considered well-lit and requires little or no additional lighting during daytime.

The next generation of building Codes and Regulations are expected to consider daylight holistically, including: building location, facade orientation, visual comfort, glare and aesthetic considerations together with the energy related implications.

Central atria are a common feature today in public buildings. They are used as multi-functional circulation spaces in the centre of large multi-storey buildings. A well-designed atrium can bring daylight into internal spaces. For sloped glazing the recommended minimum pitch is 15°. If designing any shallower, then insist on manufacturers watertight test results.

Many rooflighting products have weak points, so unless your glazing system comes with a thermal diagram which identifies the 10° isothermal line, you may have issues where condensation can occur causing mould and algae growth. Especially a problem when specifying rooflights to kitchens and humid bathrooms. Thermal models need to state the internal and external temperature conditions, otherwise they are meaningless.

For improved energy efficiency and much better control of the indoor environment, better airtightness standards are required than the acceptable limits set by the Building Regulations. If you are aiming for [email protected] for the whole build, then you will need to pay attention to elements such as windows and rooflights which could potentially jeopardise your building air tightness if the product interface is not robust or the results depend too much on the quality and experience of the installation team. The regulations allow for opening vents to be sealed up – consider specifying opening vents which are air tight tested and compliant when closed.

To avoid glare, it is important to co-ordinate your lighting strategy to balance any dark spots between rooflights. It is over brightness of daylight and sharp contrast between dark and light areas which cause the most glare.

Acoustic performance inside your building depends on outside noise levels and the frequency of that noise. An open window is modelled to provide a sound reduction of around 15dB, a typical rooflight – up to around 28-32dB Rw and a higher performing glass roof (when closed) approx. 36-45dB Rw.

For domes, watertight testing does not simulate extreme weather and do not take into account the effect of wind. Consider specifying rooflights which are watertight tested against driving rain.

Specify non-fragile assemblies for new and replacement roofs. Although Polycarbonate rooflight suppliers may claim the material on be non-fragile, for the purpose of safety, they will rarely be impact resistant against falls. If the rooflight assembly is not fall-through proof, it is a fragile roof. One additional safety feature is permanent fall-through protection grills.

There are a host of exciting materials to choose from when designing your atrium and rooflight solutions so consult with manufacturers to take advantages of their knowledge and experience as a ‘free partner in your design and development team. Getting their input on your specification prior to tender can save a lot of trouble later on in the process if things have been overlooked. Ask manufacturers for independent product test results including verification of their CE label declaration of conformity. The best way to get verification on product performance claims is to model products which are on BIM with all their performance characteristics.

Lamilux UK Ltd

Tel: 01284 749051