Zenon Rooflights


In this section we have answered some of the most frequently asked questions associated with Rooflights and the Zenon product range.

If there are any questions that you feel are unanswered we are always happy to help, you can contact us here.

What is the difference between rooflight and roof window?

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.

What is the difference between a rooflight and a skylight?

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

What is the difference between transparent and translucent?

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.

What is the difference between GRP and polycarbonate rooflights?

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

What is CE Marking?

‘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.

What is cost balance light vs heat?

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.

What is the highest non-fragility rating for a rooflight?

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.

At what temperature do GRP rooflights melt in a fire?

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.

Do you offer bespoke rooflight manufacture?

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.

Why are Zenon Rooflights not clear and does that mean I don’t get as much natural light in my building?

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.

What roof pitches are your rooflights suitable for?

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 ArcContact us for further information.

Have all Zenon rooflights been tested?

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.

What guarantees do Zenon rooflights come with?

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.

What type of rooflight do I need to use in a low pitch/standing seam roof system?

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.

The rooflight needs to cover an opening more than a metre wide. What are my options?

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.

What span can we achieve with your in-plane rooflights?

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.

Why use Zenon Evolution in favour of Zenon Pro when the light transmission is worse?

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.

Why can I not find Zenon Archlight?

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

Is a 10mm 4-wall polycarbonate a better insulation layer than the 4mm twin-wall option?

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.

Design Considerations
The specification asks for ‘walkable’ rooflights. Will your rooflights meet this requirement?

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.

What percentage or area of rooflights should I use?

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.

What is the Daylight Factor for your rooflights?

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.

What is ‘diffused’ light and how can I be sure I’m getting what I need?

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.

How diffused is the daylight that your rooflights deliver?

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.

What is the uniformity factor for your rooflights?

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.

What does U-value mean?

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 mper temperature degree difference. It is an essential consideration of the building design under Building Regulations.

What is best, high levels of light transmission or better U-values?

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.

What is best, small areas of rooflight with high levels of light transmission or larger areas of rooflight with better U-values but lower levels of light transmission?

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.

Do your light transmission figures make an allowance for dirt and debris?

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.

What is the ƒ-factor for your rooflights?

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.

How can your rooflights reduce energy bills?

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.

Rooflight Installation
How is my rooflight delivered?

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

How do I safely handle my rooflight?

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.

How do you support rooflights?

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

Are there any special storage requirements for rooflights after delivery to site?

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

How do I install my site-assembled rooflight sheets?

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

How do I install my composite panel (FAIRs) rooflights?

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

What are the minimum end overlap lengths for in-plane Zenon rooflights?

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.

Do I need to use stainless steel fasteners to install GRP rooflights?

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.

Do I need to use saddle washers to install GRP rooflights?

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.

Do you need to drill oversized holes installing your rooflights?

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

I am using a walkable metal liner, can I drop the safety nets?

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.

Rooflight Maintenance
How should you clean rooflights?

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.

What happens if a rooflight gets damaged?

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.

How do I know if my roof is leaking or just condensation?

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.

How do I avoid condensation in large metal buildings?

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.

It’s too hot in my building, can I paint the rooflights to reduce the heat?

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.

Are your rooflights labelled so our maintenance engineers can see how old they are?

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.

How do I repair a rooflight that has been damaged?

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.

Rooflight Replacement and Refurbishment
Rooflight Maintenance and Damage Repair
We have a customer that complains of the building being too hot in the summer months. Can I paint over the rooflights?

Solar over-heating can be worsened by the inclusion of large areas of rooflights, however the heat from the sun is also likely to be passing through the rest of the roof and wall cladding and contributing to this and adding to any internal heat gains. For most of the year, the heat from the sun passing through the rooflights is a good thing and can significantly reduce the heating required.

Rooflights that have been covered over cannot usually be easily uncovered and recovered to suit the changes in weather, and any coating applied to the rooflight may only have a short effective period. The preparation and application also risks damage to the rooflights and foreshortening their service life. A better approach is to consider improving the ventilation provision to the building.

Is there any real benefit of replacing rooflights rather than just cleaning them?

This depends on the condition of the rooflights. GRP rooflights that are 30 to 40 years old or more will often have deep engrained dirt and staining in the surface and may have also have noticeably darkened. Rooflight replacement creates easily obtained benefits in the internal working environment of the building in addition to reducing the energy consumption used in both heating and lighting.

Is it not better to clean and coat the rooflights with a glaze rather than attempt to replace them?

This approach can extend the life of the rooflights and reduce the frequency of cleaning old rooflights to maintain good levels of light transmission. However the total cost associated with these works and the lack of any guarantee on the applied coating generally means that it is much more cost effective to replace them with a new product carrying a guarantee on service life.

How do I repair a rooflight that has been damaged?

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.

I have a newly installed composite panel rooflight that has been damaged by other trades or persons unknown. Removal and replacement of the whole panel is expensive and disruptive to the newly installed roof. What else can I do?

One consideration, depending on the extent and location of the damage, is to remove the fasteners, thoroughly clean the surface and install a new single layer of matching rooflight profile over the top. The fasteners should be inserted in a new location or over-sized options used in the same hole, and the full perimeter of the additional layer sealed to the existing rooflight to prevent the ingress of water and contaminants.

What is the highest non-fragility rating for a rooflight?

The test and classification for non-fragility is detailed in a 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.

When refurbishing a roof, do I have to use the strongest and safest rooflights possible?

No. There are different options of weights and types of rooflight available that will all be safe, but if the roof might already be fragile, especially in the case of fibre cement sheeting, the classification of the rooflight can be regarded as no better or safer than the worst part of the roof.

How can I tell when a rooflight has become fragile?

For over 20 years now rooflights supplied by members of the National Association of Rooflight Manufacturers (NARM) have been designed and tested for long periods of non-fragility, subject to specification, but many other factors can impact on this.

It is often likely to be the case that this is not possible to identify by means of inspection only how strong and non-fragile a rooflight might be, and if in doubt, the whole of the roof including the rooflights should be treated with caution. It is possible that an old rooflight can still be structurally very strong, but deterioration of sealants and the corrosion and/ or loosening of fasteners in the metal or fibre cement sheeting together with the corrosion of unseen internal components can result in unsafe roof assemblies.

Is it better to fit protective safety systems over the top of old rooflights?

There may be in some cases where roof access is not limited to those properly trained and knowledgeable about roofs, but generally not. These systems can significantly reduce that very important free resource of daylight and make effective cleaning difficult or impossible.

Rooflight Replacement – Design Considerations
Will increasing the rooflight area not increase the cost of heating the building?

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 insulation values caused by the increased rooflight area. Even with low energy LED lighting systems, this often only reduces to three times the cost. It is usually more cost effective to save on lighting cost rather than heating costs.

What options are there to reduce the heat loss through the rooflights without noticeably reducing the light transmission?

Most solutions involve increasing the layers within the rooflight cavity, but every layer reduces the light transmission. The Zenon Insulator product works in a different way and traps air in small transparent cells. This significantly reduces the convection currents carrying heat through the rooflight without adding more and more layers.

When the rooflights need to comply with Building Regulations, what should the minimum U-value be?

Building Regulations Approved Document L2B that covers existing buildings other than dwellings requires rooflights to have a minimum U-value of 1.8W/m²K when assessed in the horizontal plane. The guidance given in BR443 provides for a 0.3W/m²K adjustment to a triple skin rooflight giving a 2.1W/ m²K minimum value. Hambleside Danelaw quote all U-values in the horizontal plane unless otherwise required.

Do I need to improve the thermal performance of new rooflights compared to the existing ones?

As a general rule, rooflights that are being replaced due to damage need only be replaced to the same standard of the damaged rooflight.

Where a series of rooflights are being refurbished to improve their performance and the daylighting within the building, then they should be upgraded to comply with current Building Regulations minimum standards wherever practicable. The requirement should also take into account the cost of the actual work and expected payback period and whole project cost.

Dependent upon the scale of the work, the cost involved and the expected payback period. In many cases, some improvement to the thermal performance can be quite simple, straightforward and cost effective to be of benefit the building anyway.

The customer would like the rooflight area to be increased. Is this possible?

Where the building may only contain small areas of rooflights, such as the old ‘rule of thumb’ 10%, in most situations increasing the rooflight area can reduce the need for artificial lighting, particularly if there are areas that are gloomy and not well lit.

Is it a good solution for single skin rooflight applications to install specially manufactured rooflights with double or triple skin panels that fit between purlins?

This method can certainly improve light transmission and reduce heat loss and condensation, however there will still be significant cold-bridging on the purlin where the rooflight remains single skin. The localised condensation may, at certain times of the year and depending upon building use, lead to dripping of the condensate.

Can I just replace the outer skin of composite panel rooflights?

No. These rooflights are supplied as a pre-assembled panel. To remove the outer skin, the whole panel would require removal.

Rooflight Replacement – Specification
Can Hambleside Danelaw provide me with the correct specification of rooflights for my rooflight replacement project?

There are many permutations and combinations of rooflight specification available to suit all needs and different criteria. The Hambleside Danelaw Technical Manual provides comprehensive guidance on the performance expectations for different combinations of rooflights. However, we are not building designers and so the final decision on rooflight specification must be decided by the contractor carrying out the work.

How can we identify what the metal profile is?

Sheet profiles can be identified by measuring key dimensions – cover width, pitch (distance from one corrugation to the next), depth of profile, crown and trough widths etc. Because many profiles have a similar shape and appearance to others, the dimensions should be measured accurately and to the nearest 1mm as possible. We carry over 600 profiles in our range and can assist with profile identification.

What information do you require for a rooflight replacement order?

For in-plane rooflights to match new metal sheeting or composite panels, or where the profile is known, you need only state the manufacturer, profile and lengths needed, plus box depths and filler positions for composite panels. Don’t forget to allow for the minimum recommended end lap distances.

Post Refurbishment
We have refurbished the cladding of a building and now the occupier is experiencing more condensation in the rooflights. Why is this?

It is possible that when an over-cladding system has been installed and significant improvements to the insulation made, the internal air temperatures become significantly higher and for much longer. These higher temperatures allow the air to contain much higher levels of moisture which in turn may pass through the tiniest of holes or breaks in the sealant between sheets and then condense in the roof build up where it can only be seen in the rooflight cavity.

Sometimes when a building changes its use from one function to another, and the occupants are using processes or equipment that give off more heat than the original building use, condensation issue may arise that were previously not present.