Introduction to Daylighting with Rooflights - National Association of Rooflight Manufacturers (NARM)

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Background

Welcome to an introduction to daylighting with rooflights. In this seminar will be looking at the benefits of natural daylight and explaining the basics of designing daylight into buildings with rooflights. The content of the seminar is relevant to stages 0,1 and 2 of the RIBA plan of work and is applicable to domestic and non-domestic projects.

By the end of the seminar:

  • You will have learned about how daylight affects human health and well-being and how rooflighting can play a role in supporting this requirement.
  • You'll gain an understanding of how rooflights can help to achieve the required light levels for specific building usage.
  • You’ll be made aware of the important role that rooflights can play in reducing energy usage and CO2 emissions.
  • And you'll learn about how to apply the knowledge you've gained when designing or specifying rooflights.

 

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Agenda

The seminar comprises five modules as listed here with a brief summing up at the end of the program. Please note that all the technical data contained within this program is freely available from NARM, references will be provided at the end of the program. Before we start, I'd like to give you a brief introduction to NARM the National Association of rooflight manufacturers.

 

What is NARM?

NARM is an active trade Association representing UK rooflight suppliers and associated businesses. Our membership includes manufacturers and installers of glass polycarbonate and GRP rooflights suitable for all kinds of buildings, as well as manufacturers of rooflighting materials. Our aims are to promote best practice in rooflighting and to provide impartial information to specifiers. Our technical committee has been directly involved in discussions with DC LG the department for communities and local government, which has responsibility for building regulations, with regard to amendments to Part A, Part B and Part L of the building regulations. For many years we've liaised directly with DC LG and BRE the contractors who developed the SBEM software to assist with the development of a SBEM to ensure that it correctly reflects the positive contribution of rooflights in achieving Part L compliance.

 

Daylight in the Built Environment

 

Daylight is Critical to Health and Wellbeing

Sunlight plays a vital role in human health and while in recent years there has been publicity about the potentially damaging effects of UV causing sunburn, the World Health Organization states that in fact a markedly larger global disease burden results from inadequate exposure to daylight. Exposure to sunlight enhances mood and energy through the release of endorphins. In fact, daylight is critical to mental well-being, as evidenced by the growing understanding of the condition known as SAD seasonal affective disorder, caused by inadequate exposure to daylight. Daylight is also recognised as contributing to healing processes and fighting infection.

 

Daylight and Health Through Human History

The beneficial effects of the sun and daylight to human health and well-being had been recognised for thousands of years. Ancient civilizations developed architectural and cultural traditions exploiting and celebrating daylight. During the Middle Ages or what had become known as the dark ages, this wisdom lost some momentum. However, in the Renaissance. Which followed daylighting became an aspirational feature in stately homes and public buildings as the beneficial effects were again highly valued.

 

By the mid-19th century the medicinal and healing properties of light started being appreciated again and understood by healthcare pioneers such as Florence Nightingale. In the 1920s a new architectural language exploiting the virtues of daylight was championed by architects such as Lucca Boozier. The advent of air conditioning and the introduction in the 1930s of fluorescent lighting enabled architects to design deep plan buildings with a reduced need to exploit daylight. However, by then the increased recognition of daylight as a basic necessity for healthy living with it an increase in rooflighting in these types of buildings. This raises an important point about the role that rooflights play in introducing daylight into buildings.

 

The Role of Rooflights in Daylighting

This and the following diagrams represent single storey buildings or the top storey if in a multi storey build. In smaller buildings vertical glazing may be adequate but only for areas within six metres of a window. With deeper plan building’s rooflighting or a combination of both roof and wall glazing are needed to achieve recommended daylight levels. We’ll get into more detail about daylight design with rooflights later in the program, but first let's take a look at how daylight affects today's building occupants.

 

Daylighting Benefits in Residential Buildings

High profile TV shows about home design and self-building, place lighting at the top of the priority list for domestic properties. Where it is now taken for granted but high levels of daylight make abroad contribution to health, well-being and general quality of life. More and more research into daylighting is revealing that daylight plays an important role in the success of buildings in all sectors. 

 

Daylight benefits in healthcare buildings

In healthcare environments the benefits of high levels of daylight are particularly significant and include:

  • improved post-operative recovery;
  • rates reductions in average inpatient stays;
  • less requirement for pain relief;
  • increased resistance to infections;
  • positive effects on mental health.

 

Studies show that even when patients are unconscious, they benefit from exposure to natural daylight.

 

Daylight Benefits in Educational Buildings

Studies carried out in educational establishments show that natural daylight contributes significantly to improved concentration among students. Well daylit classrooms were typically shown to provide a 21% improvement in learning rates and daylight has also been demonstrated to contribute to reduced absenteeism and improved behaviour.

 

Daylight Benefits in Retail and Commerce

In retail environments the concentration and performance of workers have been proven to be superior to those where only artificial light is present and there is compelling evidence that shoppers in retail environments generally stayed longer and spend more where there are high levels of natural daylight. In fact, there is a well-documented correlation between the presence of rooflights and retail sales. This can be attributed to a greater sense of well-being in these stores as well as improved presentation of products.

 

Daylight Benefits in Industrial Buildings

In factories and warehouses high daylight levels contribute to increased productivity; improved levels of safety; and reduced absenteeism. So, the benefits of daylighting in terms of health and well-being are now well documented across all sectors but there's another extremely important factor that's been the subject of significant research over the last two decades, and which plays an increasingly important role in building design today and will continue to do so in the future.

 

The role of rooflights in energy saving and emissions reductions

 

Rooflights Contribute to sustainability

Rooflights save energy and reduce CO2 emissions, making them a critical contributor to meeting Part L of the building regulations covering the conservation of fuel and power. NARM commissioned independent research which illustrated the energy savings offered by the effective use of daylight. These findings were subsequently referred to by the government and the BRE and reflected in Part L of the building regulations. NARM continues to play an advisory role in this respect.

 

Research Findings - Highlights

Independent research carried out by the De Montfort Universities institute of energy and sustainable development, proved conclusively that rooflights can save energy in many applications and generally speaking the greater the rooflight area greater potential savings. There is however a law of diminishing returns as the rooflight area increases and there is a limit before overheating may become an issue. So, an optimum area needs to be identified. It should also be noted that the building regulations Part L and the equivalent regional regulations specified minimum insulation values for different rooflighting applications. Consult your rooflight supplier regarding insulation values for specific products. When used in conjunction with automatic lighting controls to turn the electric lights down or off, rooflights can have a major impact on the overall energy consumption of a building, cutting energy costs by reducing the need for the use of electric lights.

 

Global impact of Artificial Lighting

Lighting represents nearly 20% of global energy consumption so, reducing this demand by introducing more daylight into buildings should be a priority for specifiers. The amount of energy needed to light a building artificially is often much greater than the amount of energy used to heat it, and maybe the greatest single energy use in operating the building.

 

How Rooflightarea Affects CO2

This graph shows how the total CO2 emissions vary with rooflight area. The graph has been created using SPEM software as specified by the building regulations for a building which is identical to the notional, except for the varying rooflight area. The redline shows emissions from heating energy, the yellow line shows emissions from lighting energy and the green line shows total emissions, which is the title of heating plus lighting energy. The dotted blue line shows the 100% value below which compliance is achieved.

 

The rooflight area of the notional building set by building regulations is 12%. So, because the results shown after a building where all other aspects are identical to the notional building, when the rooflight area is 12% emissions are exactly the same as the notional building and are exactly 100% with the green line intersecting with the dotted blue line. It can be seen that with no rooflights the total emissions are approximately 40% higher than a building with 12% rooflights. In fact, the emissions due to the lighting system alone are higher than the total emissions for the notional building. This demonstrates that for some buildings regulatory compliance is impossible without rooflights. For the same reason it may be impossible to achieve higher BREEAM ratings if rooflight area is not sufficient.

 

You can gain a deeper insight into rooflighting and energy efficiency by referencing the further reading documents listed here. NARM technical document NTD 6.2 is entitled designing with rooflights supporting Part L building regulations and NT D 10 is an independent report by Elmhurst energy on improving daylighting and lighting controls on existing nondomestic buildings.

 

Rooflight systems and applications

A huge variety of rooflight designs are available to suit all different kinds of roof constructions from pitched, slate or tiled roofs, to flat roofs, profile metal roofs, as well as self-supporting glazed structures, of almost any shape or description.

 

Glass Rooflights

First let's have a look at glass rooflights. These are generally the preferred option for domestic commercial and retail applications where aesthetics high performance and long working life are key considerations. Glass rooflight designs range from single pane modular flat glazed rooflights to pitch structures and pyramids and multifaceted designs.

 

A number of rooflight suppliers are now able to offer specialist glass rooflights which are designed to floor loadings to accommodate deliberate and regular foot traffic, for applications such as roof terraces these are known as walk on traversable rooflights. There not to be confused with conventional rooflights, which may be classed as non-fragile. Glass is the only glazing material which can accommodate walk on rooflights.

 

Polycarbonate Rooflights

Polycarbonate glazing is available as solid profiled or multi world insulating sheets in a wide range of tints and options. It's suitable for a variety of applications across many sectors and offers extremely high impact resistance and durability over a service life of 20 years or more. Polycarbonate glazing can be specified for applications requiring nonfragile rooflights.

 

It can be installed as flat sheets or cold bent on site to produce curved barrel vault rooflights or other designs. Solid polycarbonate sheet can also be thermoformed to manufacture Dome or pyramid modular rooflights, or profile sheets.

 

GRP (Glass Reinforced Polyester) Rooflights

GRP or glass reinforced polyester is a tough and durable material manufactured by encapsulating glass fibres in a thermoset resin. It's tough and durable and has a long working life up to 25 years or more and can be specified for applications requiring nonfragile rooflights.

 

GRP rooflights are available in hundreds of profiles to match fibre cement and metal roofing profiles so they can be installed as part of the slope of the roof. They provide excellent light diffusion, avoiding hotspots or harsh shadows making them an ideal roof glazing material for industrial buildings and warehouses as well as agricultural buildings. GRP also offers excellent chemical resistance so may require fewer special precautions than other materials in industrial applications.

 

Glazng Materials Comparison

More detailed comparisons between the characteristics and suitable applications of different glazing materials are available in this technical document, which can be downloaded from the NARM website.

 

Rooflighting Design Basics.

In this section we will be looking at the factors that need to be considered when designing with rooflights.

 

Building Usage

The starting point for any roof ight specification is the usage of the space to be lit for example, in domestic buildings and for feature glazing and atria there may be a requirement for building occupants to be able to see the view beyond the rooflight, making clear glazing the obvious choice.

 

Clear Glazing = Direct Light

Clear glazing whether glass or polycarbonate delivers direct light which passes through windows or rooflights without disruption or interference, entering the structure as a straight beam. This can result in uneven distribution of light with unwanted glare or shadows and localised heat build-up. So, these factors must be considered if specifying clear glazing although in some applications direct light can be used creatively to highlight building features or to create effects.

 

Diffusing Glazing = Practical Daylighting

Diffused light is scattered as it passes through the rooflights giving a more even distribution of light into the area below and avoiding unwanted heat build-up, glare or strong shadows. A wide variety of light defusing glazing materials are available including tinted, etched or patterned glass and polycarbonate and as mentioned in previous section translucent GRP.

 

For the majority of rooflighting applications in which the quality of the light is more important than the view, diffuse daylight is the more likely choice. Commercial and industrial buildings educational establishments, retail premises, leisure centres and many other types of building, will benefit from high levels of diffused daylight. So, having determined the appropriate type of light. The next consideration is how much light is required?

 

How much light is required?

This table shows the recommended light levels in Lux required for different activities as listed in the CIBSE guide A. These values provide a guide by which we can determine the appropriate design and rooflight area for a given application. Typically, 200 Lux is the absolute minimum lighting requirement for occupied internal spaces, where there's no requirement for visual tasks requiring detail perception. For general retail and manufacturing areas 500 Lux is the recommended level.

 

Where accurate colour judgment or perception of movement are required the recommended level is 1000 Lux and for engineering, craft and design studios and other areas where perception of intricate detail is required, the recommended level is 2000 Lux. Achieving this level of illumination for close detailed work would usually require supplementary localised task lighting, In addition to the background lighting. It's worth noting that high light levels are also required for good colour perception, as well as detailed work and all types of rooflight can provide very good colour rendering index.

 

Calculating the correct rooflight area to achieve the desired light level is the next stage to consider. Generally speaking, the larger the rooflight area, the more hours each year, the required light level will be reached. However too large a rooflight area, can result in unwanted overheating so there needs to be a balance. 

 

Recommended Roolight Areas

This graph shows how rooflight areas will affect illumination levels. In this example for a single storey building located in London between the hours of 6:00 AM and 6:00 PM daily with rooflights providing 50% light transmission, you can see that as the rooflight area along the bottom of the graph increases the length of time a given illumination level is achieved is extended. So if you're designing for 500 Lux looking at the yellow line you can see that with 10% rooflights 500 Lux would be achieved for approximately 2000 hours or 46% of the working year, and if that rooflight area is increased 15%, 500 Lux is then available for just over 2500 hours or 58% of the working year. So, 15% rooflight area provides 500 Lux for 26% longer than a 10% rooflight area.

 

Integration with Artificial Lighting

Rooflights can never provide all the illumination required so it's important to consider how they will form part of an integrated strategy. Rooflights only save energy when electric lights are switched off, so to achieve the optimum savings and automatic lighting control system actuated by light sensors should be employed so lights are only switched on when light levels drop below the desired level.

 

Rooflighting legislation and standards

 

Building Regulations

Rooflights are subject to mandatory legislation and standards covering the key performance factors, and care should be taken to ensure their specified accordingly.

 

These requirements include:

  • minimum insulation values,
  • safety,
  • fire performance
  • security.

 

Minimum Insulation Values

Minimum insulation values for rooflights are specified in the relevant regional Part L building regulations or section 6 Reckitt regulations in Scotland, for example for new build non domestic applications in England and Wales, the minimum U-value must be 2.2 watts per square metre kelvin which, will necessitate triple skin plastic rooflights or high performance double glazed glass units.

 

Safety

To comply with CDM regulations and other safety legislation rooflights should usually be specified to be non-fragile in accordance, with the ACR red book test. In addition, glass rooflights should comply with the requirements of the scattering CWCT technical note 92, which is cross referenced from the ACR red book.

 

Fire Performance

Fire performance should be specified to comply with Part B building regulations usually necessitating a class 1 inner skin and SAB outer skin in accordance with BS476.

 

Security

Rooflights on new build domestic properties are now also subject to legislation covering security as outlined in the relevant regional Part Q building regulations.

 

Quality Standards

With an increasing number of construction products coming into the UK from all over the world, it's important to recognise the appropriate UK quality standards for rooflights. Your rooflight suppliers should be an ISO 9001 accredited company or be working towards this accreditation. Rooflights should be CE marked where the appropriate standard exists for the specific rooflight type. Rooflights should not be CE marked where there is no appropriate standard. Clarification on which rooflights should carry CE marking is available on the NARM website. Independent accreditation schemes such as the British Board of Agrement and the British Standards Institution also provide evidence of quality standards compliance. Although these are only appropriate to high volume standard products not bespoke designed items as many rooflights are.

 

Summary

So that brings us to the end of our introduction to rooflight specification. Before we finish, I just like to quickly recap on the subject we've covered today:

  • In module one - we talked about the benefits of natural daylight in terms of health and well-being, and the practical benefits of reduced energy consumption and emissions, as well as other things like improved aesthetics and building immunity.
  • In module two - we explained how rooflights can play an important role in reducing energy requirements and emissions and, we looked at how rooflights can therefore make a positive contribution to regulatory compliance in this respect.
  • In module three - we looked at the different types of rooflights available, in particular the glazing materials used, how they differ and suitability for specific applications. In module four we outlined the basic factors affecting rooflight design and specification, with details of light levels required, recommended rooflight areas and other considerations including control of artificial lighting.
  • And finally, in module five - we took a brief look at the regulations and standards pertaining to rooflights in the UK.

 

We hope you found this presentation interesting and informative. For more information on any aspect of rooflight specification, please direct your enquiries to admin@narm.org.uk and a representative of NARM's technical committee will contact you. It's also worth noting that many NARM member companies have CPD seminars for which they should be contacted directly.

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