Keep an eye on the sky

With climate change at the forefront of everyone’s mind, Natalie Goodridge of Lamilux UK looks at how buildings and their components – such as skylights – need to be futureproofed and designed to withstand extreme weather events

Residential, industrial and commercial buildings must all adapt to an increasing change in weather conditions. Due to climate change, extreme weather conditions such as heat waves, stronger storms and colder winters are becoming more frequent. It is also important to remember that although solar gains may be considered desirable during winter, this can result in overheating of the building during the warmer periods and a subsequent increase in the building’s energy usage to cool the internal space.

The use of skylights within the overall building design enable greater use of natural daylight and are becoming increasingly important in architecture. On flat roofs, skylights such as rooflight domes, barrel vault rooflights and flat glass skylights are specified to introduce both natural daylight and ventilation into buildings. The benefits of well-designed daylight and ventilation levels to the internal environment of a building are well documented and include improved productivity and performance within education and workplace settings.

In order to futureproof against climate change, water tightness, air tightness, resistance to wind loads and thermal performance are all important factors to consider when specifying rooflights or roof glazing for your project.

Water & driving rain

Water and driving rain tightness is an important criteria to consider when specifying rooflights for the future. Tests confirming this requirement are described in EN 12208. This standard classifies windows and facades according to their resistance to pressure, the method and the duration of the test. In addition to the application of water on all sides and at different angles, the pressure difference inside/outside is also tested in order to simulate the impact of wind. To simulate possible scenarios with storms and heavy rain as realistically as possible, standing water is sucked in on weather seals or on profiles deformed under wind load.

Air tightness

High performing thermal insulation within the exterior walls is of no use to the building if the skylights or other building components and their connections are extremely permeable to air. There are special test standards for individual building elements such as windows to determine and classify their air tightness. EN 12207 describes a test procedure in which the air volumes related to the area and perimeter of the product are determined in various positive and negative pressure stages. The products are then categorised into Classes 1 to 4, with Class 4 representing the highest air tightness. The standard does not apply exclusively to glass skylights, however rooflight companies such as Lamilux choose to prove the achieved airtightness, and therefore test the glass skylights following the window standard. The same applies to glass roofs which are tested using the facade standard.

Wind load

Strong winds will introduce stresses to the components of buildings, and can cause them to weaken over time. In addition to the geographical location, building shape and height, other influences such as the type and distance of surrounding buildings also play a major role. Skylights and their fastenings must therefore be sufficiently resistant to wind loads with performance testing to EN 12210 and EN 12211. For this testing, wind deflection results are grouped into Classes of A, B and C, with A being the lowest standard. Pressure, meanwhile, is grouped into 5 Classes: again, Class 1 is the lowest level of performance.

Thermal protection

Another relevant property of skylights regarding environmental impacts is thermal protection. The total energy transmittance, or g-value for short, is used as a measure of the energy transmittance of components such as glazing. This common value expresses what percentage of the energy striking a glazing unit reaches the inside. Simply put: How much of the heat radiation reaches the inside of the building.

The g-value is a number between 0 and 1 – the lower the total energy transmittance, the lower the heat input. There is a difference between summer and winter thermal insulation. This is because in summer the heat should be kept outside, whereas in winter the heat radiation of the sun should be let in. That’s why it is desirable to have the lowest possible figure in summer, whereas in winter, the opposite is necessary. In addition to the possibility of using special sun protection glass, interior and exterior shading can also be considered.


The benefits of well-designed ventilation levels to the internal environment of a building are well documented. Due to the variety of skylight designs and combined opening options now available to use within an overall building construction, skylights are an extremely efficient method of introducing adequate ventilation to an internal space. Natural ventilation improves the quality of air within a building. Good levels of ventilation impact directly on individuals’ performance and health and well-being. This is particularly beneficial during hot summers. Both natural ventilation, and smoke ventilation can be implemented in any type of building with vented roof lights such as modular skylights, glass atria or barrel vault rooflights.

With climate change increasing the chance of extreme weather events, architects should ensure that specified building components are both durable and function in a way to protect against such environmental impacts by conforming to relevant standards.

Natalie Goodridge is marketing manager at Lamilux UK