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CPD: The Environmental Benefits of Rooflights

CPD Seminar

Article as published in Construction Manager - May 2013

This article looks at the case for daylight; rooflights and their influence on low carbon buildings and finally design of rooflights and the variety and options available.

Building regulations and rising energy costs are dictating a shift in the need for daylight in commercial buildings. Technical Director of Brett Martin Daylight Systems, Bill Hawker, casts a ray of light onto the energy saving benefits of rooflights and explains how daylight delivers environmental benefits in more ways than one.

Daylight has a crucial role to play in the environmental impact of buildings and their activities, not least of which by reducing demand for electric lighting and thereby massively lowering CO2 emissions and cost.

Rooflights can cleverly capture and utilise daylight which, even with our unpredictable weather, is free and abundantly available while adding a stylish design feature to almost any roofline. From schools and retail sites to warehousing and sporting facilities, the necessity of designing with rooflights should be an early consideration.

Daylight benefits

The infusion of daylight into any building will not only lessen the need for expensive, energy-hungry electric lighting, but will also help inhabitants feel good and work more efficiently.

Natural daylight provides active light which constantly changes colour, intensity and direction, stimulating the eye and mind. It has enormous physiological benefits, enabling the body to produce vitamin D and triggering the release of serotonin, the hormone which influences our feelings of wellbeing.

In schools, daylight has been scientifically proven to improve the attention spans of children. The Department for Education and Employment quote that: “The school designer should assume that daylight will be the prime means of lighting when it is available,” in Building Bulletin 90, Lighting Design for Schools.

In the workplace, higher daylight levels lead to better productivity and less absenteeism, while one American survey found that retail buildings with skylights sold 40% more product, partly due to shoppers lingering longer in daylight. Sporting facilities too benefit from rooflights which help us focus on the action in indoor arenas and let light onto the pitch at stadiums.

Lighting level is measured in ‘LUX’ and requirements will vary depending on a building’s use; 100-200 LUX for example would be sufficient where little perception of colour or detail is required, such as loading bays or boiler room areas, whilst a lighting level of 750–1,000 LUX is needed for difficult visual tasks and accurate colour judgement and is often specified for retail environments or inspection areas. Brett Martin’s technical expertise can help specify an appropriate rooflight to cater for every eventuality.

Simply put, by increasing daylight levels you will create an environment people want to spend time in.

The advantages of rooflights

Rooflights can be the only way of introducing natural daylight into many building types, including agricultural structures, warehousing, large retail properties and sporting venues.

While windows or vertical glazing are obvious ways of letting daylight in, natural light can only reach six metres from a window into a room. A rooflight will capture light no matter where the sun is and can fill even the largest structures with light.

Crucially, the introduction of natural daylight, when combined with modern lighting controls, allows electric lighting to be reduced or turned off whenever daylight is available. With electric lighting usually claiming the lion’s share of a building’s running costs, dramatic savings in energy and resulting CO2 emissions can be made by combining rooflights with a modern lighting control system. Rooflights can in fact positively contribute to the BREEAM sustainability ratings of new non-domestic buildings.

Independent research: Rooflights save energy

Independent research carried out by De Montfort University to assess the impact of rooflights on reducing buildings’ CO2 emissions proved conclusively that rooflights, when combined with appropriate lighting controls, save energy.

This is based on hour-by-hour analysis over a 12 month period of buildings with rooflights covering between 0% and 20% of the roof area. Increasing the rooflight area from zero to 10% significantly reduces emissions, which continue to reduce as rooflight area increases to 15%, and to 20% for higher illumination levels.

In summary, a well designed building with a good spread of natural light; typically 15-20% of the roof area in rooflights, will ensure sufficient daylight enters and reduce the need for artificial lighting. Working with a member of NARM, the National Association of Rooflight Manufacturers, at early specification stage will pay dividends in maximising energy savings and achieving regulatory compliance. Brett Martin Daylight Systems is a long-standing member of NARM and can undertake calculations to demonstrate the rooflight area required to meet a building’s lighting requirement.

Regulatory requirements

Reducing carbon emissions is paramount to achieving Part L Building Regulation compliance. This legislation, geared to save energy and power consumption in buildings, stipulates that major savings need to come from building services such as lighting and heating.

SBEM software is used to accurately calculate and set a building’s CO2 emissions targets based on a Notional Building – Part L specifies a Target Emissions Rate (TER), which all new non-domestic new builds must perform at least as well as. The Notional Building uses a rooflight area of 12% and a rooflight U-value of 1.8W/m2K. Crucially, it also includes lighting controls to minimise the use of artificial lighting.

(A U-value is a measure of heat loss – the higher the U-value the worse the thermal performance. The worst acceptable rooflight U-value permissible in Part L is 2.2W/m2K.)

It is worth noting though that if all elements specified in Part L operated to their worst acceptable standard, a building would not meet its overall performance requirements. Specifying larger areas of rooflights or rooflights with lower U-values (provided this does not compromise light transmission) will therefore boost efforts to meet a building’s TER and achieve compliance. NARM’s guidance when designing with rooflights is to consider 15-20% rooflight coverage.

Complementing systems

The interdependency of building systems, especially lighting controls, is of paramount importance in maximising the benefits of rooflights.

Data from SBEM ‘With Lighting Controls’ shows a building achieving its TER with 12% rooflight area. As rooflight area is reduced to 0%, CO2 emissions increase, with emissions from the lighting system alone over twice as high as they are with 12% rooflights.

In the ‘No Lighting Controls’ comparison, CO2 emissions remain high even with an increase in rooflight area, as manual controls result in electric lighting being forgotten and left on for most of the day, whether required or not.

Rooflight misconceptions corrected!

Rooflights don’t leak heat

The dramatic reduction in electric lighting achieved by incorporating rooflights more than offsets any smaller increases in heating requirements, while solar gain during daylight hours can in fact contribute to a reduction in heating costs.

Regulations dictate the thermal performance of rooflights and Brett Martin rooflight options provide features to satisfy and exceed minimum U-values, including thermally broken kerbs, multiwall kerbs, double glazed glass and triple and quad skin plastic glazing.

Large glazing doesn’t have to cause overheating

While solar gain can be a benefit, it is important to avoid excessive glazed areas which could cause overheating and increase loads on cooling systems. Take early manufacturer’s advice to ensure the appropriate rooflight size, glazing, and ventilation options are specified.

Rooflights are sturdy

Brett Martin Daylight Systems was instrumental in developing the ACR[M]001:2005 drop test which defines three classes of non-fragility; A, B or C. Class C is achieved when a 45kg weight is dropped from 1200mm height and the rooflight remains intact after five minutes. Class B is when it remains intact after a second drop, while Class A records absolutely no damage. While no rooflights are classified as Class A, neither are most roof constructions without rooflights.

There’s plenty of daylight

While we may sometimes struggle to see the sun, there’s still plenty of daylight. A rooflight will capture light whether the sun is shining or not, though it is fair to point out that windows are equally acceptable if exterior walls are within six metres and can sometimes offer a better view.

Rooflight varieties and options

There are an infinite variety of rooflight shapes, sizes, colours and glazing options to suit flat, pitched and curved roof applications.

There is no definitive rule as to which rooflight fits which application best but, as the only European manufacturer of all the main plastic glazing materials (polycarbonate, GRP, PVC), Brett Martin offers unbiased advice on rooflight styles and glazing choice.

For pitched roofs, suitable rooflights for ridge rooflighting include skylights, dual pitched skylightspanel glazing systems and barrel vaults. Alternatively, rooflights for the roof slope could include mono pitch skylights, panel glazing systems, barrel vaults, suntubes, or factory or site-assembled profiled rooflights.

For curved roofsbarrel vaults or dome rooflights are hugely popular while flat roofs can benefit from domes, skylightsbarrel vaults or suntubes.

Canopy rooflighting is also available for stadia and walkways.

Rooflight glazing material choices include polycarbonateGRP (glass-reinforced plastic); or glass. Each offers differing properties in regard to durability, light transmission level, solar control, thermal and acoustic performance, ventilation options and aesthetic appeal. Brett Martin’s technical experts are at hand to give impartial guidance from specification, to installation, and beyond.

Avoid the pitfalls

As we’ve seen, there are many design and performance factors to consider when specifying rooflights. Working with a reputable, NARM registered manufacturer at an early stage will pay dividends in ensuring regulatory compliance and peace of mind over performance, installation and guarantees.

RIBA CPD seminar from Brett Martin, entitled Specifying Rooflights to Meet the Demands of the Next Generation, further supports the case for rooflights and is available to book click here