Shedding light on the case for rooflights

Rooflights are now an essential element to consider in modern designs, says John Godley of Hambleside Danelaw Building Products, explaining the reasons why

Rooflights play a vital role in the modern building, but are often overlooked. They are the common link to many aspects of building design and can help the designer, the building owner and the occupier achieve a more sustainable, energy efficient and enjoyable place to work and to live in. Well considered rooflight design, done at the outset of the building concept can have dramatic effects on all aspects of the building from the owner’s potential asset value to the well-being and productivity of the occupants. Buildings that provide high levels of natural light are more positive working environments than those which are dependent upon artificial light. It is known that people respond better to working in natural light conditions, as the eye and brain functions work better, resulting in improved concentration and overall performance. Plus, of course, less dependency on artificial light significantly reduces energy consumption and running costs as well as impacting positively on a building’s overall carbon footprint. In new buildings, where high levels of insulation are now being installed, the most significant savings in energy can be realised through the utilisation of the free resource that is natural daylight. The energy consumed by artificial lighting far exceeds the relatively small amounts of heat energy that are lost through increasing the rooflight area, which is a small part of the whole building fabric. The amount of energy required to light a well-insulated building is far greater than the amount of energy required to heat it, and can be the greatest single energy use in the operating the building. Of course, artificial lighting will always be essential in most occupied buildings subject to requirements, particularly in the winter months or in areas where localised specific or constant lighting levels are required, but even low energy lighting systems can create relatively high energy demands. This is even more likely when the lighting is turned on and left on throughout the daylight hours irrespective of need, and where automated lighting controls have not been incorporated into the design. Thermally efficient insulated rooflights can further reduce heat loss and energy consumption. The effectiveness of rooflights as a contributor to energy efficiency are acknowledged in the Building Regulations Approved Document Part L. It recommends that industrial and commercial building structures should have a rooflight area of 10 per cent to 20 per cent, subject to limiting solar gains. Research by De Montfort University and published by the National Association of Rooflight Manufacturers (NARM) demonstrates the savings that can be made by increasing rooflight areas.

The graph below demonstrates the reduction in CO2 emissions of a typical notional building as the rooflight area is increased to the optimum 16 per cent to 18 per cent, and used in conjunction with a fully automated lighting control system.

Rooflights are a simple and cost-effective choice to introduce a more even and useable distribution of natural light, particularly in large structures where light is required deep into the building or in enclosed areas that cannot be lit through an external wall. Increased areas of light-diffusing rooflights, often with lower light transmission or improved thermal performance, can optimise the energy performance of the building, and there are many permutations of performance to choose from. Reduced areas of rooflights with high light transmission levels and poor diffusion that create glare and hotspots, while still leaving areas of shadow and gloom that must be overcome with localised artificial lighting, only demonstrate poor consideration to the daylight design.

Another element to consider is a BREEAM assessment. Many local authorities now insist on this before they will give planning permission, therefor it is vital to optimise the rooflight design, distribution and product type. Using rooflights with low or reduced embodied carbon is a further example of good product selection that can have a significant effect on the BREEAM assessment. Ultimately, the key considerations for specifiers are as follows:

  • Clients need buildings to meet stringent regulatory requirements that will continue to tighten – or even exceed them.
  • Achieving a BREEAM rating of ‘Excellent’ as opposed to ‘Very Good’ can make a significant difference to the developer who is looking to let a large industrial or warehouse building to a prospective client.
  • Having a building that is lit by natural daylight will improve the efficiency, productivity, mental alertness and the general health of the occupants that work in the building.
  • In combination with good air-tightness and low fabric U-values, a reduction in the use of artificial lighting is the best way the building occupier can lower the energy cost of running the building.

When considering the design of a building it is now vital that rooflights, rather than being an afterthought, are treated as an essential design element right from the start.

John Godley is technical manager at Hambleside Danelaw Building Products