CPD 10 2020: Daylight design for commercial buildings using structural glazing

This CPD, sponsored by VELUX Commercial, explains how the maximising of daylight through bespoke structural glazing can improve wellbeing and productivity of a building’s occupants as well as cutting energy costs, and sets out the specification considerations

Introduction

This CPD will explain the importance of structural glazing, examine the role of natural light in building design in terms of productivity, health and wellbeing, and consider how bespoke glazing can inform the design process.

People benefit from daylight. Clearly there is a need for electricity to illuminate places of work, but if a building is able to use specialist glazing to maximise daylighting as part of its fabric then its occupants stand to gain on a number of fronts.

Commercial and industrial buildings used daylight as a free light source for centuries. But over time, methods to bring light into interior space changed with advances in materials, technologies and construction. As industries rapidly grew, the requirements for building envelopes changed and the use of daylight for illumination was pushed aside with the emergence of electrically powered artificial lighting.

That is changing again, with a return to greater use of daylight, although we may never eradicate the need for artificial energy to illuminate and heat or cool our indoor spaces. Designing daylight into the fabric of our buildings is now considered a key component of good commercial building design.

Structural glazing represents a flexible solution that can balance an architect’s freedom in design against the need to support a commercial building’s energy and lighting strategy as well as its overall performance.

The importance of light in architecture
In simple terms, light enables us to see. It stimulates our visual system to process and interpret images. In this context illumination is a sufficient supply of light to allow us to experience space, objects, textures and colours.

The visual qualities of daylight are exploited in architecture for the aesthetic dimensions they add to the exterior of the building or the internal space. Natural light can be amplified to harmonise or contrast exterior and interior spaces, to create shadows, manipulate the space, and highlight or understate texture or colour. Designers use daylight to explore aesthetics and to evoke a mood or a sensual response.

Non-visual stimulation is the effect of light on our other physiological and psychological functions. Since humans first took shelter indoors, our predecessors have instinctively preferred daylight over the artificial light of a fire, for example. We seek daylight because our biological responses evolved upon changes in light quality caused by weather or the changes of the seasons.

Although some of the characteristics of daylight can be mimicked by artificial light, the visual and non-visual benefits of daylight cannot be reproduced artificially. Applying daylight-focused thinking is key to achieving truly human-focused building design.

The importance of daylight design within the commercial sector
The design of commercial spaces is often influenced by commercial pressures and the need to fulfil a building’s intended function as efficiently as possible. Case studies show that improved daylight design increases individual productivity by as much as 23%, reduces sick building syndrome (SBS) symptoms as well as absenteeism, and reduces annual energy loads by between 27% and 88% (Herschong et al, 2002).

Most architects and designers are familiar with the best practice of designing for daylight provision in commercial spaces. Improving illumination levels, however, is only a part of the daylight design concept, and the new European Standard EN 17037 has extended its scope to target multiple aims in respect of daylighting and occupant comfort.

EN 17037 addresses four key areas: daylight provision, assessment of views from windows, access to sunlight and prevention of glare. The minimum performance level is set out, but a medium or high level can be targeted, depending on the specific requirements of the project.

A study by Romm and Browning (1998) reported that companies in buildings where daylight was prioritised reported lower absenteeism, increased productivity and fewer mistakes. Providing a healthy environment has a positive effect on business growth. Returns on the initial investment in appropriate glazing solutions that offer improved daylighting, thermal comfort, acoustic balancing, air quality and exterior views will be seen continually over a building’s lifetime.

A study conducted by Imperial College London three years ago found that addressing all these areas would mean a productivity improvement of between 5% and 8% of business turnover. The college’s report also suggested that the payback period for initial investment into the design or an upgrade of a building was as little as 24 months.

The flexibility of EN 17037, with its wide scope that targets multiple aims in respect of daylighting and its different performance levels, is particularly helpful in commercial design. While many aspects of daylighting strategy will be identical across industries, there are considerations that vary according to building type, leading to differences in emphasis.

For instance, in warehouses, airports and other buildings where optimum visibility is essential for workplace safety and workforce efficiency, rooflighting is called for because of its ability to provide twice as much daylight as vertical glazing. Combining roof glazing with facade glazing can help to reduce glare and provide high illumination levels, which is useful in sports venues and leisure facilities where excellent visibility is important for customer experience and retention. The views of the sky that rooflights offer can provide a sense of connection with nature that enhances this effect further.

What is structural glazing?
Structural glazing systems are streamlined systems that are fixed and installed in various ways that ultimately suggest they are part of the fabric of the building. These systems allow commercial buildings to have windows as walls and roofs, and walls and roofs as windows, while holding structural elements together to create a strong and secure building envelope. The level of design customisation means such systems can provide the exterior of the building with a more homogeneous finish, one that reduces as much as possible any visual separation between the facade and the roof.

The flexibility of structural glazing offers an ever-expanding array of opportunities for innovative architectural design. Various options are available that provide the flexibility many architects desire when looking to specify a system that fits the design and performance requirements of the brief.

Bespoke structural glazing – the imagination knows no bounds
Bespoke structural glazing systems give architects the ability to choose the ideal span, size and shape of the opening. The location of the opening is flexible in relation to the building envelope, and the glazing can be customised to fit the desired surface curvature or roof pitch. By eliminating the need to finalise the glazing solution at the conception stage, the designer is given the freedom to remain faithful to their vision.

Such a bespoke approach to structural facade glazing changes the sheet of glazing that envelops the building to open up exciting design possibilities. Curved or radiused external glazing – or even multiple curvatures – can be deployed, and non-rectangular or more irregular shapes can be used for multifaceted facades. This allows an attention-commanding look that adds dimension to the building.

Being able to use a wide variety of shapes increases the ways in which daylight can be used internally for asymmetrical light distribution to increase visual comfort. In roof applications, asymmetrical light can help with the transition from light to dark. It also softens shadows and makes for a better experience, for example in a large stadium, a theatre or a museum.

The freedom to create non-standard shapes and sizes also allows the glazing to fit better to the building’s function and design concept. For example, the far-reaching light used in the atriums or walkways of commercial spaces can create a feeling of synergy and connection between the occupants and nature.

Structural glazing – more than enhancing lighting
Maximising available daylight is just one of the advantages of structural glazing. A major factor behind the growing use of structural glazing in modern architecture is its loadbearing capacity. At the conception stage it is vital to take a holistic approach, with structural glazing considered as part of the building’s fabric. The loadbearing capacity of a system can be used to reduce the use of steel structures that would be needed to support a glazing solution.

Depending on the rafter depth used and fragility rating required for the design, the span and size of each glazing unit can be considerably larger than with standard glazing products. Using such systems across commercial buildings results in improved daylight quality, as well as reducing obstructions to external views, enhancing occupants’ connection with nature.

The choice of glazing material will be guided by the functionality of the building and its design specification. Various materials have different fragility classifications, and guidelines issued by the National Association of Rooflight Manufacturers set out the fragility tests. CWCT TN66/67 relates to glass and ACR [M] 001-2019 to polycarbonate. These determine the maximum size of the glazing pane, whether glass or polycarbonate, to support the intended roof function.

The non-fragility classifications for roofs are:

• Class 0: Rooflights are effectively walk-on solutions.
• Class 1: Rooflights allow walk-on for maintenance purposes only, with full safety kit to be worn.
• Class 2: Rooflights are not designed to be walked on, but they are able to take impact in the event of maintenance personnel falling upon them – in this case the outer toughened pane of the glazed unit may break, but the inner laminated pane is designed to prevent a fall for 30 minutes.
• Class 3: Under no circumstances should these rooflights be walked upon. These solutions should also have a barrier around them or be on an upstand sufficiently high enough to ensure they cannot be walked or fallen upon.

In the case of polycarbonate glazing the Class B Non-Fragile to ACR[M]001:2019 Test for Non-Fragility of Large Element Roofing Assemblies should also be used.

Safety considerations should always be at the forefront of glazing specification, but this is a small price to pay for the limitless design possibilities that various glazing options can offer for the external visual appeal of a commercial structure.

Conclusion
It has long been accepted that people benefit from natural light. It brings us closer to nature – outdoor space – and this improves our wellbeing. When we are disconnected from the outdoors we suffer from the lack of daylight, which brings disruptions to our natural cycles of sleep and alertness.

In addition, it is worth considering that daylight is free energy. It makes sense commercially to build spaces where the use of daylight can improve energy usage, which allows buildings to be more environmentally resilient and future-proof.

Bespoke structural glazing can offer levels of customisation that give the designer carte blanche to achieve their vision, regardless of how unusual or complex such a vision may be.

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