FAQs

Zenon GRP rooflights are a thermoset material, rather than thermo plastic, which means that they do not soften or melt in high temperatures. They are available in a range of fire classifications to suit different applications.

Generally, ‘rooflights’ or ‘skylights’ are components installed in roofs to let daylight into a building where windows cannot be installed or are insufficiently effective. Roof windows tend to be installed in pitched slated or tiled roofs. Usually the can be opened in the same way as a window, used primarily in dwellings.

They are basically the same thing, however smaller individual units with transparent apertures tend to be referred to more often as ‘skylights’.

No light transmitting materials allow 100% of the light to pass through due to surface reflectance and some absorption. However, with transparent materials there is usually no perceptible spreading of the light. Diffusing materials can vary in the degree in which light is scattered through them, and this gives the appearance of translucency when the image cannot be viewed in sharp focus.

You can find a comparison of the two materials in our GRP vs Polycarbonate sheet – to view, please click here.

‘CE’ is the abbreviation of French phrase “Conformité Européene” which literally means ‘European Conformity’. All construction products that are covered by a harmonised European Standard must be manufactured and assessed against the Standard and carry the CE mark to be sold in Europe. This is covered by the Declaration of Performance (DoP) for that product.

In a typical industrial shed building with high bay sodium lighting, the energy consumption of the artificial lighting is often around four times that of the energy lost through the reduced thermal performance of the rooflights compared to the well-insulated areas. Even with low energy LED lighting systems, this often only reduces to three times the cost. Therefore it is better to save money on lighting cost rather than heating costs. For more FAQs on design considerations, you can click here.

The test and classifications for non-fragility are detailed in a publication known as the ACR(M)001 ‘Red Book’. Broadly speaking, the highest classification for most roof assemblies will be Class B.  It is a classification for the whole roof assembly irrespective of the presence of a rooflight, so a rooflight cannot have a better classification than the roof it is fitted into.

Class A is only achievable if no element of the roof assembly is damaged during the ACR test – something that is generally only possible with roof constructions designed to resist high impact loadings such as those with concrete decks and rooflights designed for floor type loadings. For more information on this subject, check out the ‘Non-Fragility’ section of our technical manual.

Span capabilities vary by profile depth and weight of rooflight sheet.  Maximum span recommendations can be found on our product data sheets, which can be emailed to you via our Zenon sales team.

Zenon Arc is a factory-built panel barrel vault rooflight system available in double skin configuration manufactured using either the Zenon Pro or Zenon Evolution type materials and with the choice of two additional ‘Insulator’ upgrade options. It is manufactured to accommodate spans or 1.0m or 1.2m and is extremely quick to install on site.

Zenon Evolution might not always be the best choice for the project, however it brings many benefits. The glass reinforcement comprises continuous strands that run the length and width of the rooflight providing greater levels of tear resistance and greater safety without having to make the rooflight thicker. This means that it can be manufactured to a sharper profile shape to match the metal sheets better, under at the top and over at the bottom. This makes the sealing of the rooflight easier and more reliable.

Due to the increased glass content, the level of light transmission through the Evolution product is less, but the diffusion is greater. Lower levels of light transmission result in lower levels of solar heat gains, therefore greater areas of rooflighting can be used to improve the uniformity of light within the building and avoid areas of shadow.

The stronger thinner product uses less raw materials which reduces the amount of embodied carbon in the product and can also be more cost effective compared to thicker alternatives. Please see FAQs about design considerations, for more information on why specifying rooflights is an important component within building design.

Due to customer feedback, Zenon Archlight Barrel Vault Rooflight is now called Zenon Curve to avoid confusion with Zenon Arc Barrel Vault Rooflight.

As an insulant, yes it is, but for the marginal improvement in the heat that is retained by it, the extra layers that both absorb and reflect light mean that the light transmission losses are higher. For some designs, this would be a sound solution, but in many cases the light improvement and lower embodied carbon of the lighter product delivers a better result.

For the best of both worlds, consider the use of Zenon Insulator. This can deliver improved U-values with minimal impact on light transmission, so the best of both worlds.

We have tooling to match the vast majority of fibre cement and metal roofing profiles. If we don’t have the profile you need, we can produce the necessary tooling  at a cost depending on the quantity required. Sheet lengths are generally manufactured from 1.2m to 7.5m but can be made them shorter or longer to meet specific requirements. There would usually be additional cost associated with this. Please contact us for more information.

Zenon rooflights are manufactured from translucent, naturally-diffusing GRP. The light levels passing through Zenon rooflights can be comparable to transparent materials, subject to weight and specification. Unless direct vision is required through a rooflight, then diffused light is a more appropriate option. The light is scattered over a wider area reducing the uncomfortable effects of hot spots, glare and gloom within the building.

In-plane GRP rooflights are not recommended for use in pitches below 4°, although some system manufacturers may allow this, subject to the limits of their system guarantee.  They can also be used as ‘wall lights’ in vertical cladding applications where required.  For roofs with a pitch below 4°, or for some specialised roof systems, kerb-mounted barrel vault rooflights are often the best option. We supply a GRP barrel vault rooflight system, Zenon Arc. Contact us for further information.

Yes. Rooflights must be tested for light, heat and solar transmission properties, together with fire performance. They’re are also tested for non-fragility in a representative assembly of the different construction details required for that system.

Zenon rooflights have either a 25 year or 30 year Service Life Guarantee dependent upon choice of material.  Project specific service life guarantees can be issued for inclusion in O&M manuals upon request. As manufacturers of components fitted into or onto roof assemblies by others, we cannot offer any guarantees on non-fragility as there are too many factors beyond our control.

We can supply certain rooflight profiles to match these metal roof profiles, however there are usually strong technical reasons where this is not the best approach, and ‘out-of-plane’ barrel vault systems mounted on kerbs such as Zenon Arc would be a more appropriate solution. Please contact us to discuss your requirements.

Some roof sheet profiles are more than 1 metre wide as standard and we have tooling to make many such products. Often the rooflight pattern of an installation can include two or more rooflights adjacent to one another, depending on the daylighting requirements within the building. For other roof types, Barrel Vault Rooflights, available for daylight opening widths of up to 4 metres, may be the best option. Please contact us to discuss your requirements.

This would depend on the use of the building and being able to strike the best balance of rooflight specification choice for that building. Insufficient rooflight areas can lead to areas of gloom and shadow that requires the use of artificial lighting to overcome poor or inadequate daylight distribution. Using rooflights with high levels of light transmission in only small areas can increase the risk of glare and visual discomfort making the space in the building unusable.

A rooflight area at a minimum of 10 to 12% floor area would often be a little too low with the optimum being around 16 to 18% floor area. If better light distribution is required further, then the rooflight area can be increased, but solar gains would need to be controlled by using solutions with lower levels of light transmission.

No, as this would be impossible due to different environments, cleaning regimes etc. When designing for the building’s energy performance, it is prudent to apply a ‘maintenance factor‘ depending on the location and environment of the building.

The ƒ-factor of a product or assembly is an internal surface temperature comparison against outside air temperatures to determine the risk of surface condensation. For a well-insulated wall or roof, the ƒ-factor would be close to 1 and condensation unlikely. A poorly insulated element or cold-bridge may have an ƒ-factor of 0.5 or less.

Rooflights, by their very nature, are unable to achieve the very low U-values of the opaque parts of the roof and still allow light transmission. Typically, a rooflight with a U-value of 1.8W/m²K would have an ƒ-factor of 0.82 and a rooflight with a U-value of 0.8W/m²K would have an ƒ-factor of 0.92.

For more information on this subject, please see the Thermal Transmission section in our Zenon Technical Manual.

Not many construction products can deliver something valuable that is entirely free.  Maximising the benefit of this natural resource, in conjunction with automated lighting controls, can save more energy in a building now that increased levels of insulation are delivering significantly reduced returns.

During the colder months, rooflights can still contribute to the heating of a building through solar gains. The use of a rooflight with good levels of light transmission and improved thermal performance to reduce heat loss can deliver significant savings.

No rooflight supplied for any roofing application should be walked on unless specifically designed to do so. Only glass rooflights designed to floor-loading type applications should be considered for this use. No rooflight suitable for use in lightweight metal clad buildings can be considered suitable.

It is important to understand the difference between ‘walkable’ and ‘non-fragile’. For further guidance see the ‘Non-Fragility’ section of our Technical Manual.

That would depend on the operational requirements for that building and the specification of the rooflight because there are several options to suit different requirements. The provision of natural daylight rather than artificial light has been demonstrated to deliver more energy savings than can now be achieved through increasing insulation levels.

Studies have demonstrated that the optimum rooflight area is usually in the region of 12 to 18%. At higher rooflight levels, consideration should be given to the risk of solar over-heating at the hottest times of the year, and the ventilation strategy for the building.

The Daylight Factor cannot be stated for any stand-alone product. It is a comparison of the light levels experienced throughout a building as a percentage of the daylight that is available outside the building.

A room or building with a daylight factor of less than 2% will generally appear gloomy and artificial lighting will be required for most tasks, compared to a daylight factor of more than 5% where it will appear strongly lit and minimise the requirement for artificial lighting providing that the light is uniformly distributed.

For more information on this subject, please see our ‘Estimating for Daylight Factors’ guidance document.

Diffused light is a soft light with neither the intensity nor the glare of direct light. The light is scattered when passing through diffusers and naturally diffusing materials such as GRP and avoids glare and harsh shadows giving a more even spread of light throughout the building. Diffused daylight is always recommended as the best option for rooflighting unless there is a requirement for a clear uninterrupted view through the rooflight. Diffused light can be anything from quite lightly diffused delivering an identifiable amount of light spread, up to heavily diffused where the light distribution is so widely scattered that its limits are difficult define.

The diffusion in GRP materials is created by the refraction of light passing through the resin and glass. The more changes that the light passes through, the more diffused the light becomes. Where diffusion may be stated as 100%, this has no useful meaning as it ignores any reference to how widely and evenly the light is diffused.

Uniform lighting, whether by natural daylight or by artificial lighting, is important where there is a requirement to operate in an environment with significant differences in lighting levels.

Changes between well and poorly lit areas, especially where glare occurs, can cause significant eye discomfort, leading to stress and tiredness and therefore potentially jeopardizing safety as the human eye takes its time to adapt to changing lighting conditions.

The uniformity factor can be expressed as a ratio of the highest to lowest illuminated area in a given room or space. The closer it is to one, the more uniformly lit the space is. It is therefore the design of the daylighting rather than a function of the rooflight itself. Increased rooflight areas with high diffusion and lower light transmission levels provide the most uniform lighting, or highest uniformity factors.

It’s a measure of the rate of heat flow through the building fabric or a building component; the lower the U-value or rate of flow, the better the insulating ability.  Thermal performance is expressed in units of energy (Watts) per m² per temperature degree difference. It is an essential consideration of the building design under Building Regulations.

Generally, more energy is saved by reducing the energy consumed by artificial lighting than is used for heating purposes. Low U-value rooflights are not always the best solution for a building if the light transmission is reduced. The more layers added into a rooflight, the more the light transmission is affected. The Zenon Insulator® core can be used to overcome this issue.

The material and performance of the fastener is not something that we would generally specify or make any specific recommendations on other than following recognised good industry practice.

It is generally now accepted that for cladding systems and rooflights incorporated into them to meet their long-term non-fragile expectations of up to 20 years and longer, then good quality stainless steel product should be used.

For further guidance on fasteners, sealing washers etc, and their suitability for the application, please refer to the appropriate fastener manufacturers.

Saddle washers are not required with Zenon rooflights.  The recommendation on all GRP trapezoidal profiles is to fix in the trough of the sheet, using a self-drilling, self-tapping fastener with a minimum 29mm diameter washer.  Saddle washers are only required where an oversized hole should be drilled prior to installation in products such as polycarbonate where there are large differences between the contraction and expansion of the materials in use.

No, it is not necessary with GRP rooflights but may be a requirement with other rooflight materials.

As a component manufacturer, we are not in the position to advise on risk assessments and method statements for construction for site works. Please remember that rooflight panels installed in ‘walkable’ liner systems should still not be walked on.

They usually arrive palletised on a truck. Any access limitations on vehicle size or delivery times should be advised at the time of order.

Rooflights should usually be carried on their edge and in accordance with the pallet labelling. Rooflight sheets and panels are relatively lightweight for their size and therefore special care is required in windy conditions, especially on the roof.

All Zenon rooflights should be handled, stored off the ground and adequately supported in accordance with the pallet labelling until installed.

All rooflights should be stored off the ground and under cover to protect from UV and weathering prior to installation.

Click here for installation guidelines and drawings for Zenon site-assembled rooflights.

Click here for installation guidelines and drawings for Zenon composite panel rooflights (FAIRs).

In accordance with recommended industry practice, and to ensure that the expected non-fragile rating is achieved, sufficient overlap should be allowed for on-site tolerances so that the fasteners can be installed a minimum of 50mm from the sheet end. For site assembled rooflights, we normally recommend that the sheets be ordered to provide a 150mm minimum overlap to the outer sheets and 100mm minimum for the liners.

Composite panel rooflights, or FAIRS, are best ordered with provision for a 150mm overlap, and purlin spreader plates or ledger angles provided to ensure adequate support of the panel ends. Please see fitting instructions for site-assembled and composite panel rooflights.

Generally, and to maintain the non-fragility status of a rooflight, any damaged rooflights should be replaced. The need to ensure that the non-fragile status is maintained means that repair kits can no longer be used effectively. Hambleside Danelaw publish separate guidance on assessing and dealing with rooflight damage.

Zenon rooflights can be cleaned with a mild detergent or soap solution and a soft bristled brush.  Care must be taken to prevent any damage to the surface film protection. Separate details are available upon request. Pressure washing should not be used on metal cladding systems or rooflights used in metal cladding systems due to the risk of damage to surfaces and seals.

To preserve the non-fragility classification and service life guarantee, in most instances rooflights would require replacement. Small areas of damage that appear slightly cloudy or as a ‘bloom’ where the structure of the rooflight sheet has not been compromised, and the surface film is undamaged, do not generally require any remediation. Any more serious areas of damage where the rooflight appears to be white or crystalline in appearance, or where the surface film is damaged normally require replacement.

Suitable repair systems that might be available or offered on the market do no carry any guarantees of value and their application may cause further detriment to the product.

Rooflights should ideally be inspected on delivery and should not be installed wherever any damage exists. For further information, please refer to the Zenon document covering this subject.

This is not always obvious, as cooling due to rainfall can cause condensation. If a rooflight is leaking, it will generally correlate regularly with certain weather conditions, even if not immediately obvious. Condensation is more likely to occur during colder weather and damper conditions irrespective of rainfall. The appearance of green algae in a rooflight assembly is more likely to indicate a leak from the outside.

There are several factors that can cause condensation, and low levels that occur at the coldest times of the year are sometimes unavoidable. Condensation can be due to the internal humidity levels, the use and activity of the building, a lack of ventilation, poorly insulated building elements, cold bridging in the construction or high temperature differences between inside and out.

The risk of condensation can be significantly reduced by using well insulated metal roof and cladding systems and by ensuring that the rooflights in these systems deliver the required thermal performance.  In situations where there is risk of condensation, rooflights that are better insulated than the minimum regulation requirements will reduce the risk and amount of condensation likely to occur. We offer a comprehensive range of rooflight thermal performance options. Click here to contact our technical team to discuss.

Painting or coatings may be applied, but the effectiveness of these solutions may be very short term with little or no guarantee and could result in insufficient daylight at other times of the year when it is required. The only effective way of reducing heat transfer through rooflights is by reducing the light passing through the rooflight.

Consideration should also be given to the internal heat gains and ventilation strategy of the building, and it should also be considered that lightweight clad buildings are at a greater risk of overheating from the sun irrespective of the presence of rooflights.

Any coating applied may not adhere adequately to the surface, or may require to surface of the rooflight to be damaged as part of the preparation process and therefore invalidate both the manufacturers service life guarantee and degrade the non-fragile performance.

This kind of information should be contained in the building records or building maintenance manual. Our rooflights are printed along their edge with identification marks, relating to the manufacture and specification of the product.

This can only be applied to the outer surface of the sheet, and where it will remain visible after installation, will also be exposed to UV attack and weathering and therefore may become illegible long before the rooflight becomes unserviceable.

No. Please see Q&A below.