CPD articles

CPD: Rooflights

1 March 2013

• How daylight can enhance work and leisure environments
• The role rooflights can play in reducing carbon emissions
• How to install them effectively

Click here to be taken to the online CPD test paper for the March 2013 issue

Building regulations and rising energy costs are dictating a shift in the need for daylight in commercial buildings. Bill Hawker explains how rooflights can help buildings deliver environmental benefits and regulatory compliance.

Daylight has a crucial role to play in the environmental impact of buildings, not least by reducing demand for electric lighting and thereby lowering carbon dioxide emissions and costs.

Rooflights can cleverly capture and utilise daylight which, even with our unpredictable weather, is free and abundantly available. They also add 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.

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 light 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.

Rooflights at Oakfield school, Wigan

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

In the workplace, higher daylight levels lead to better productivity and less absenteeism, while one survey conducted in the US found that retail buildings with skylights sold 40% more, partly due to shoppers lingering longer in daylight.

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.

Rooflights can be the only way of introducing natural daylight into many building types, such as 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.

Rooflights can, in fact, positively contribute to the BREEAM sustainability ratings of new non-domestic buildings.

Saving 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 an hour-by-hour analysis over a 12-month period of buildings with rooflights covering between 0% and 20% of the roof area. Graphs 1 and 2 show CO2 emissions through the roof structure for both 300 Lux and 600 Lux lighting levels.

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 the National Association of Rooflight Manufacturers (NARM), at early specification stage will pay dividends in maximising energy savings and achieving regulatory compliance.

Graphs 1 and 2: How rooflight area affects carbon emissions

Regulatory requirements

Reducing carbon emissions is paramount in complying with Part L of the Building Regulations. 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.

Simplified Building Energy Model (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 highest 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.

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

Data displayed in Graphs 3 and 4 is taken 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 as we’ve seen, 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.

Graphs 3 and 4: How lighting controls reduce emissions against a notional building

Rooflights: key facts

Heat loss 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.

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.

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. Seek manufacturer’s advice early to ensure that the appropriate rooflight size, glazing and ventilation options are specified.

Rooflight resilience 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 1,200mm 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.

Blue tinted glass reinforced plastic canopy glazing at Brighton & Hove Albion FC’s Amex Stadium

Rooflight varieties and options

There are many rooflight shapes, sizes, colours and glazing options to suit flat, pitched and curved roof applications.

For pitched roofs, suitable rooflights for ridge rooflighting include skylights, dual pitched skylights, panel 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 roofs, barrel vaults or dome rooflights are hugely popular while flat roofs can benefit from domes, skylights, barrel vaults or suntubes. Canopy rooflighting is also available for stadia and walkways.

Rooflight glazing material choices include polycarbonate; GRP (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.

Bill Hawker is technical director of Brett Martin Daylight Systems


Case study: Mardome units light up £5m community building

Hoe Valley Community Building where rooflights have been installed in the green roof and provide daylight for facilities including the boxing club (below)

The Hoe Valley Community Building in Woking is a new £5m facility providing a permanent home for nine local community groups, including the District Scouts, Air Training Corp and Army Cadet Force and Woking Boxing Club. It boasts 41 architecturally inspired Brett Martin Mardome Ultra rooflights, which not only provide the centre with a wealth of natural daylight, but also maximum security, high insulation and flexible ventilation.

The dome rooflights, which have been installed in both the planted and non-planted areas of the green roof, were specified because of their ability to significantly enhance the building’s aesthetic appeal, as well as contribute to its high performance qualities. The triple skin Mardome Ultra achieves a U-value of 1.8W/m2K, while the powered opening of the rooflights ensures there is a wealth of natural ventilation — both factors which helped contribute to the centre being awarded a BREEAM “very good” rating.

Timothy Passingham, associate at HLM Architects, said: “We initially approached Brett Martin when its rooflights were recommended by the manufacturer of the barrel-vaulted standing seam roof. We wanted an affordable, secure and highly insulating maintenance free solution to allow natural daylight into the heart of the deep plan spaces and the Mardome Ultra was the ideal choice.”

Ease of installation was a key consideration and the units were delivered directly to the centre complete and ready to fit. The domes were supplied with a direct fix adaptor kerb, allowing the installers to attach them directly onto the builders’ insulated metal upstand which was welded directly into the standing seam roof — a contributor to the project being completed on schedule.

Community centres often attract unwanted attention from burglars so security was also a primary consideration. Mardome Ultra rooflights feature a secret lock system which allows the domes to be installed and locked securely in place, offering complete peace of mind.

Five Brett Martin Mardome Sunlight tubular rooflights were also used to provide maximum light transmission into the centre’s ground floor level. The polycarbonate dome, which is designed to facilitate fast, hassle-free installation, sits on a roof plate to collect the maximum amount of daylight possible, which is then transmitted to the interior below through a rigid aluminum tube.

Rooflight installation

All reputable rooflight manufacturers not only design and manufacture rooflights carefully to offer the best levels of illumination, insulation, ventilation and non-fragility as well as resisting design loads, but also supply these with detailed installation instructions.

Rooflights will only perform properly if these installation instructions are followed fully and correctly, and are fitted with the recommended accessories (eg fasteners, sealants and fillers). This is essential, not only to ensure rooflights are fully secured to remain weathertight and resist all design loads correctly (including wind and snow), but also to maintain safety, to ensure that once installed with the surrounding roof, the intended non-fragility classification will be achieved, and retained for the intended period.

Failure to follow installation instructions correctly can result in rooflights that are fragile, or will leak, or be unable to resist wind or other loads, or which may deteriorate more rapidly over time.

Generally, rooflight installation is straightforward and can be carried out easily by trained and experienced roofing contractors. Installers should not only install rooflights fully in accordance with installation instructions, but should do this using the safe working practices required for all work at height.

Any risk assessment should include a full understanding of when a roof assembly incorporating rooflights can be regarded as non-fragile (which may allow secondary protection to be removed), and the safe method of work must also ensure that foot traffic will be avoided on any rooflight as this may result in damage, necessitating replacement. For any refurbishment work, old rooflights should always be regarded as fragile unless evidence is available to the contrary, and appropriate precautions taken.

Some particularly large or complex skylights may be installed by specialist glazing contractors or rooflight manufacturers’ own installation teams. Special consideration may be needed, including specialised access equipment, safe hoisting to the roof of rooflight materials, temporary protection of openings prior to rooflight installation, precautions for working over open areas, and/or the need for safe working platforms (with safe access/egress) in those areas, as well as the usual requirements such as perimeter edge protection, safety nets and secure access and egress from the roof.

Roofing contractors may provide safe access and all necessary precautions for specialised staff to install the rooflight itself, or the risk assessment and method of working may be part of the installation package. Responsibilities should be clear, but the same overall requirements always apply — the rooflights must be installed in accordance with the manufacturer’s recommendations, with installation work carried out in a safe manner, with all risks mitigated as far as possible.

Click here to be taken to the online CPD test paper for the March 2013 issue


Comments

Excellent article and roof lights have often appealed to me and been used.

There is however, one small point which could be mentioned; that is the need to make some provision for cleaning. True we have very good self cleansing glass these days, if it can be afforded and meets the requirements, but frames also need to be maintained and I have found also found that some flashings do not last for ever.

I appreciate that this CPD is intended to inspire as well as educate, so keep up the good work.

Rob Visser, 22 March 2013

Interesting to understand the benefits (wellbeing ) of roof lights . Also the development of the product in relation to the materials used allowing for larger spans.

Kevin Darnell, 8 October 2013

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