CPD articles

CPD: Understanding daylighting and new standard EN 17037

4 September 2019

The role of glazing in building design is changing thanks to a new European standard for daylighting. This CPD, in partnership with Velux Commercial, looks at what EN 17037 is, why it matters and how modular skylight solutions can be used to meet the standard.

A new European Standard for daylighting in buildings is helping change the focus of building design, and the role of glazing in those designs, to improve occupant comfort and overall energy efficiency. The need to provide glazed openings and well-distributed daylight to interior spaces, while reducing artificial lighting use, has to be considered alongside the balance between heat loss and solar gains.

EN 17037 covers four areas of daylighting: daylight provision, assessment of the view out of windows, access to sunlight, and the prevention of glare. Although written for new buildings, its provisions can also be applied to works to existing buildings.

Designing buildings to provide healthy, comfortable living and working spaces is more critical than ever. The provision of daylight is one such area where design can be improved.

What is EN 17037?

Published at the end of 2018, EN 17037 is the first Europe-wide standard to deal exclusively with the design for, and provision of, daylight in buildings. It replaces a patchwork of standards across different European countries.

The UK had BS 8206-2:2008, the code of practice for daylighting, giving recommendations for daylight design in buildings – including electric lighting design when used in conjunction with daylight. By contrast, EN 17037 deals exclusively with daylight. It includes methods of calculation for design parameters that do not feature in BS 8206-2.

The benefits of modular skylights

Larger projects require more than a series of well-placed individual roof-lights. That is where modular skylights come in.

Ideally factored into the design at an early stage, Velux Modular Skylights can be linked together in combinations to suit the building shape and roof design. They are factory-made, to tight tolerances, meaning they offer consistent, repeatable and dependable performance.

All accessories, such as blinds and actuators, are installed in the factory too, so the units are delivered to site ready to be fitted.

There is no limit to the number of skylights that can be installed next to each other in a row or run – the only constraint is the building structure itself, and the effect of any movement or expansion joints. Modules of different widths are easily accommodated, though the length must be consistent in a run.

Some existing European Standards include daylight as a factor – for example, EN 12464-1 and EN 15193. However, both of these also look at it in the context of electric lighting provision, and so EN 17037 is unique in focusing on the quantity and quality of daylight for building users.

The exact date of adoption for EN 17037 depends on when it is incorporated into national standard frameworks. Standards bodies in each country must produce a national annex (NA), detailing local information that helps with applying the recommendations of the standard in the specific country.

In the UK, the full BS EN 17037 is now effective. Those parts of BS 8206-2 that conflict with EN 17037 are expected to be withdrawn.

What does the standard cover?

To achieve its multiple aims in respect of daylighting and occupant comfort, EN 17037 covers four different areas: 

Daylight provision Daylight provision, or illuminance levels, allow users to carry out tasks and play a part in determining the likelihood of artificial lighting being switched on. Assessment can be via either climate-based modelling or daylight factor calculations.

Assessment of window views Building users should have a large, clear view of the outside. EN 17037 considers the width and outside distance of the view, as well as landscape “layers” (sky, landscape and ground). The view should be perceived to be clear, undistorted and neutrally coloured.

Access to sunlight Calculating access – or exposure – to sunlight is a comfort and health factor for users of dwellings, nurseries and hospital wards. Daily sunlight exposure can be established through detailed calculation or table values. 

Prevention of glare Prevention of glare is concerned with removing the probability of glare for building users, especially those who do not choose where they sit. It uses a detailed calculation of daylight glare probability (DGP), or a standard table of values for sun-screening materials.

What performance levels does the standard set?

EN 17037 sets a minimum level of performance that must be achieved for each of these four areas. On top of that, there are two further performance levels: medium and high.

Users of the standard are free to select the performance level that best relates to the building design and proposed building use. A simplified and detailed method is available with which to assess each design area.

Roof windows deliver at least twice as much daylight as facade windows of the same size

How are local conditions accounted for?

As a standard covering all of Europe, the potential differences between one site and another are considerable. Daylight hours and angle of the sun vary for two sites within the same country, so calculation results for any of the four aspects of daylighting will be unique on every project.

The standard provides common methods of calculation for evaluating daylight. Those calculations, however, take into account national and local conditions through climate-based modelling so solutions are appropriate and specific to each project.

Daylight’s impact on building performance

While daylighting is undoubtedly a complex subject – especially when accounting for four different areas of daylight design, as covered in EN 17037 – seeking advice at an early stage and getting the benefit of daylight modelling calculations will smooth the process considerably.

Above: Glazing design is central to occupant comfort. Below: Assessment methods take into account glazing area and orientation

Getting it right at the start improves certainty. Glazing products can be specified to the right dimensions and performance level and priced accordingly. The alternative is to avoid the cost of calculations and modelling exercises, because it seems like a saving. But if late changes have to be made to a design the knock-on effects can prove even more expensive.

Daylight design for building performance

Good building design requires a balance to ensure all functions can be met together and to a reasonable standard.

In terms of glazing and energy efficiency, that balance means complementing thermally efficient, airtight building fabric with the right area of glazed openings. The result is reduced electric lighting use and avoiding excessive solar gains  – as well as giving occupants a connection to the outside.

This holistic approach is supported by whole-building assessment methods like the Standard Assessment Procedure (SAP), the Simplified Building Energy Model (SBEM), and the Passivhaus Planning Package (PHPP). All take into account glazing area and orientation as part of predicting the energy use of buildings.

SAP and SBEM form the basis for calculations in national building regulations. They are intended to be a reasonable approximation of building performance. PHPP is the foundation for the Passivhaus standard (which, contrary to the name, can be used to assess all types of buildings; a number of schools have been built to the Passivhaus standard with good results).

A natural view to the outside can impact positively on a building user’s wellbeing

Since maximising solar gains in winter, while avoiding summer overheating, is a key tenet of Passivhaus methodology, it should come as no surprise that the thermal performance of glazed openings, their size and orientation, and any shading, are key metrics in PHPP assessments.

When it comes to well-designed glazing, roof windows deliver at least twice as much daylight as facade (vertical) windows of the same size, so can help achieve required illuminance levels with a smaller total area of glazing.

Using daylight modelling to help refine the client’s brief means the balance of facade windows and roof windows can be part of initial design concepts, addressing any overheating concerns and keeping electric lighting demand to a minimum.

Daylight design for occupant health and comfort

Many aspects of human health, including the length and quality of our sleep, are linked to the light signals we receive during the day. We perceive spaces with a high level of daylight to be “better”; they enhance our mood and morale, as well as reducing fatigue.

Spaces with a high level of daylight enhance mood and morale, as well as reducing fatigue

There is no measurable universal target for the “right” light dose – but it is clear people need a greater level of interior light than is prescribed in standards for electric lighting. Daylight varies in intensity, colour and direction, and is more stimulating than artificial lighting.

In terms of a view to the outside – one of the four measures covered by EN 17037 – a number of generalisations can be made: a natural view can impact positively on a building user’s wellbeing; a wide, distant view is superior to a narrow, near view; and a diverse, dynamic view is more interesting than a monotonous view. The positive impact of daylight on building occupants is recognised by assessment methodologies like the WELL Standard and BREEAM.

Light transmittance is a key measure for glazing, but how that light is distributed is a key measure of comfort. A space is better illuminated by diffused light, whereas occupants are more likely to experience discomfort from direct light, which causes glare.

Using daylight to cut electricity demand

Using daylight to its full potential can reduce, or even eliminate, the electricity demand for artificial lighting during the day, Velux has found after investigating the effect of daylight on energy use.

A scenario was modelled where a house had no windows and light levels had to be achieved with electric lighting only. Using electric lighting influences heating and cooling demand, so the energy use for lighting, cooling and heating was evaluated together.

The results showed that relying on electric lighting to provide lux levels equivalent to daylight resulted in an energy demand some five times greater than an equivalent house with well-designed glazing and no electric lighting. Studies of office buildings have demonstrated similarly positive results, with energy savings of 20 to 60%.

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