Home > Zenon Rooflights > FAQs > Rooflight Refurbishment

Rooflight Refurbishment

Maintenance and Damage Repair

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.

Do you supply a GRP rooflight repair kit?

No. Please see Q&A below.

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.

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.

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. Replacing the rooflights 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.

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 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.

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.

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.

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.

Replacement – Design Considerations

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.

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.

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.

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.

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.

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 small transparent cells. This significantly reduces the convection currents carrying heat through the rooflight without adding more and more layers.

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.

Replacement – Specification

What information do you require for a rooflights 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.

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.

Can Hambleside Danelaw provide me with the correct specification of rooflights for my refurbishment 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.

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.

Download a brochure

Download the Zenon Brochure or our comprehensive Technical Manual

Discuss spec requirements

You can contact our dedicated technical team who’ll be glad to help

Want to book a CPD seminar?

You can fill out our online booking form and select the appropriate seminar for you

Share this page on your social networks

Main Hambleside Danelaw logo
Hambleside Danelaw Limited
Long March, Daventry, Northamptonshire, NN11 4NR, UK
+44 (0) 1327 701 900   |   +44 (0) 1327 701 909

© Hambleside Danelaw Limited