CPD 05 2021: Building considerations for commercial rooflight refurbishment

This CPD sponsored by VELUX Commercial gives an overview of the rooflight refurbishment process and the opportunities it offers to enhance daylighting and ventilation – as discussed in the company’s recent white paper

A good rooflight solution will improve ventilation and daylighting, benefiting building occupants


The provision of daylight has long been a part of commercial roof design. From small individual rooms to large open spaces, the benefits of bringing in natural light from above have long been recognised.

Providing illumination for work tasks, creating brighter and more pleasing indoor environments, or making an architectural statement – these reasons and more have informed the use of polycarbonate or glass rooflight solutions over the last few decades.

Shelter is the primary function of a roof, placing significant demands on the roof structure and its components. As part of a roof, any rooflight solution must be capable of withstanding the elements.

Even with regular maintenance and careful repair, roof coverings and rooflight systems eventually need replacing. Rooflight refurbishment can be carried out in isolation, or as part of a wider package of works involving other components such as waterproofing.

Because a roof must be considered as part of the whole building design, commercial rooflight refurbishment offers an opportunity to enhance the experience of using a building that may have stood for decades.

Growing refurbishment demand

It is expected that 75% of the buildings we use today will still be with us in 2050. The need for refurbishment design and specification solutions is therefore only likely to increase – a trend identified by VELUX Commercial in its recent white paper, Building Considerations for Commercial Rooflight Refurbishment.

Building owners and operators are faced with ensuring their assets remain functional and safe, while improving comfort for building users in the face of a changing climate.

Commercial rooflight refurbishment offers an opportunity to enhance the experience of building users

For the purposes of this CPD the term “refurbishment” is mainly focused on this adaptation of existing buildings. It can denote converting a disused manufacturing site into a new hotel, improving the performance of an existing office building, or making a retail space a more pleasing experience for visitors.

Many of the topics discussed can also relate to restoration, as in the preservation of the built environment.

Rather than adapting buildings to meet current expectations, restoration seeks to maintain buildings in a way that retains their character and historical importance. Many of the guiding principles of refurbishment may still apply, but the solutions specified could be different.

Starting out

Setting performance targets for rooflight refurbishment means first assessing and understanding the existing building, and establishing the scope of the works to be carried out.

Those constraints must then be balanced against the requirements of national building regulations and health and safety legislation, as well as any supplementary or voluntary standards that apply.

Metrics for comfort and wellbeing need to be considered, and how daylighting will be used to provide indoor environments that enhance the experience of building users. The way in which all of these different factors interact varies depending on the use of the building.

Despite presenting a variety of challenges, new life can be breathed into commercial buildings through the refurbishment of existing rooflights.

Factors influencing commercial building refurbishment

Selecting a new daylighting solution for an existing building first requires gaining an understanding of that building. Establishing the different factors that affect design and specification, and how they impact on one another, is an important first step.

The level to which the building needs to be refurbished influences which solutions are appropriate. Refurbishment ranges from the like-for-like replacement of existing rooflights to a whole-building refurbishment. From an early stage, the practicality of carrying out refurbishment works is balanced with the cost and available budget.

Take the conversion of an old production facility into a new hotel. Refurbishment on this scale means a complete upgrade of the building fabric, and a remodelling of the building’s interior to suit its proposed use. This type of work might also be driven by the need to repair an ageing building or to rectify fire damage.

New rooflight solutions might need to fit existing openings, or could be specified as part of a completely rebuilt roof. Assessing the potential solutions in the initial design can help with subsequent planning, especially through the use of modelling to assess daylight distribution and illumination, as well as building fabric performance.

There is also the building’s architectural style to consider, whether seeking to retain an existing style or create a modern aesthetic. For historical buildings, certain features or appearance might need to be replicated. Assessing the different types of rooflight material available – glass, polycarbonate, fibreglass – can help to shape early proposals.

Working with existing roof and roof openings

Where wider building refurbishment works are limited or not needed, focus turns to the roof alone. In these cases, the age, condition and make-up of the existing roof structure, roof covering and rooflight solutions will direct the extent of refurbishment that is undertaken.

Thorough surveys of existing roofs are therefore essential to identify all possible issues.

Existing rooflights could have been subject to unplanned alterations, adapted to accommodate building services (including cables, pipes and extractor fans) that they were never designed to accommodate. These adaptations need to be identified and factored into the planning of the refurbishment.

Most urgently, existing rooflights that are old or failing can present a health and safety risk to building occupants as well as a risk to the building fabric. If water ingress is presenting a slip hazard on the floor below, or reaching other parts of the construction and damaging materials and components, then prompt replacement is necessary.

Setting performance targets for rooflight refurbishment means first assessing and understanding the existing building

If the roof covering is also at the end of its service life, the focus turns to a more extensive refurbishment of the roof. The cost of erecting scaffolding and setting up the site puts an emphasis on carrying out all necessary roof works in a single programme.

The load-bearing capability of the roof also influences the weight of new solutions that can be installed. It might be necessary to mix and match products; for example, using lighter polycarbonate solutions to achieve some performance requirements but heavier glass products to achieve others.

Building operations and maintenance

For some buildings, achieving the best result from a refurbishment means allowing the building to operate as normally as possible while the work is carried out.

After the refurbishment, normal operations can include accessing the roof. Regular maintenance and repair extend the service life of roof components, and it may be that one of the goals of the refurbishment is to provide better access to the rooflights than was available before. The roof may also feature plant and services that need regular maintenance.

As well as protecting the building occupants below, new daylight solutions improve safety for maintenance operatives who access the roof. Non-fragile rooflights that meet all current manufacturing standards provide impact resistance and fall-through protection, through the use of either laminated glass or integrated netting systems.

Building regulations and other standards

When thinking about the impact of new daylighting solutions on the building in use, building regulations and standards must be considered.

Refurbishment projects can present unique challenges. The existing building – whether due to its age, condition, construction type or architectural style – can make it difficult to apply regulations fully. Regulations tend to recognise this, but it is recommended to seek professional advice regarding the proposed scope of refurbishment works and how regulatory requirements will be met.

A refurbishment solution potentially represents a significant increase in performance standards compared with the existing rooflights. That will affect the performance of the roof in which it is installed, and more widely the rest of the building fabric, which only serves to emphasise the need to think about buildings holistically.

It is equally important to recognise the limitations of building regulations. Regulations have to cover a wide range of building types and is impractical for them to provide specific guidance for every type. To meet the needs of specific buildings and end users, building regulations often reference supplementary standards.

Building regulations are often written for the short term rather than the long term. In the context of climate change, installing new daylighting and ventilation solutions provides an opportunity to think about the building performance and occupant comfort not just today, but 30 or 50 years in the future.

Rooflight refurbishment can be done alone or as part of a wider package of works

For that reason, the client and design team might choose to adopt a voluntary standard. It could be performance-based or comfort-based, and it might also seek to improve the environmental impact of the project. Examples include BREEAM, LEED, DGNB and the WELL Building Standard.

New daylight and ventilation solutions contribute to the overall rating achieved. Applying these schemes fully can be difficult when working with an existing building, but many of them include refurbishment-specific guidance.

Other areas of regulation

As part of achieving a functional, comfortable building that complies with regulations, there are other performance aspects to consider when specifying new daylighting and ventilation solutions.

Building regulations include acoustic performance targets. At roof level, this means limiting the effect of both airborne sound (including air traffic and road noise) and impact sound (rainfall or hail). And while opening windows provide ventilation, they can also increase noise levels inside.

Ventilation solutions should also not allow the ingress of rainwater, while rainfall onto a roof must be directed to a roof drainage system.

Daylight solutions also need to be watertight, and the compatibility with the surrounding roof construction is essential for a quality installation. The detailing of the junction between the roof and the rooflight solution is also a factor in thermal bridging calculations.

Finally, building regulations include structural requirements to guard against collapse and protect people in and around buildings.

When undertaking the structural design of the refurbishment, in accordance with the Eurocode and using the different parts of EN 1991, daylighting and ventilation solutions need to be capable of resisting loads such as wind uplift forces and snow loads.

Heat loss, energy efficiency and ventilation

A roof, and any rooflight solution within it, is part of a building’s thermal envelope. Global efforts to reduce emissions of greenhouse gases mean that energy efficiency standards are one of the most significant drivers of rooflight specification.

From a performance point of view, regulations require daylighting solutions to meet a specific thermal transmittance value. The scale of the refurbishment might also require that the overall energy use and carbon emissions of the building are modelled.

An adequate supply of fresh air must be maintained while minimising heat loss

Beyond that, a wider range of factors must be balanced to achieve a comfortable building. Well-designed daylighting can play a significant role in passive building design. The overall area of rooflights and their heat loss is important but solar gain can help to reduce heating demand and save energy, especially in winter.

A significant aspect of the energy performance of buildings is ventilation. An adequate supply of fresh air must be maintained while minimising the loss of heat energy overall. A successful refurbishment looks to achieve better rates of controlled ventilation without a corresponding decrease in energy efficiency.

From a comfort perspective, a controlled supply of fresh air provides connection with the outside. Comfort ventilation goes beyond simply providing a certain number of air changes per hour. Automatic operation and demand control mean building performance and comfort can be balanced without the need for user control.

Fire safety

New daylight solutions must work in combination with the roof to meet fire safety requirements, which are detailed in both building regulations and supplementary standards. The building fabric must resist external spread of flame across the roof, penetration of fire through the roof, and fire spread internally.

In the event of a fire, smoke can be the deadliest risk to building users. Smoke and heat exhaust ventilation (SHEV), provided by automatic opening vents (AOVs) that have been designed, tested and CE-marked in accordance with EN 12101-2:2003, is a critical area of rooflight refurbishment specification.

All architects and contractors are aware of the importance of fire safety regulations and standards. Working with a trusted manufacturer who can provide expert advice on how their tested components help to meet fire performance requirements of a SHEV system gives confidence that the building will perform as intended should the worst happen.

Benefits of daylighting

An improvement in daylighting is one of the biggest potential benefits of rooflight refurbishment. Better daylighting can have a positive impact on building performance as well as on occupant comfort and wellbeing.

In addition to the benefits of controlled passive solar heat gain, high levels of daylight reduce artificial lighting use and, as part of a controlled lighting scheme, the corresponding energy consumption as well. Rooflight solutions also help to balance glare from vertical windows, meaning better all-round illumination and comfort.

From a human perspective, internal environments that work with our circadian rhythms, rather than against them, are better for our health, while high levels of natural light promote alertness and concentration, which can improve learning and productivity.

Workers in an industrial setting with improved daylighting can concentrate better and be more productive

Good daylighting helps to provide a connection with the outside even though we spend around 90% of our time indoors. In the right situation, roof glazing can also provide views to the outside, enhancing the overall benefit.

Although the daylighting standard EN 17037focuses on new buildings, its metrics for daylight provision, assessment of view, access to sunlight and prevention of glare can be applied to existing buildings. For professionals less familiar with daylighting design, the standard is an excellent place to start for understanding a new way of thinking about indoor environments.


Commercial roof refurbishment generally, and rooflight refurbishment specifically, has the potential to transform buildings.

At a basic level, there is the need to achieve compliance with current regulations and standards, both mandatory and voluntary. On top of that, there is the opportunity to improve levels of comfort and safety for building users.

A good rooflight solution can mean children learn better at school, office workers are more productive, and industrial workers concentrate better throughout the day. Retail and leisure environments can become more pleasant places to spend time, and heritage buildings can be better preserved for everyone’s benefit.

Perhaps most importantly, a thoughtful refurbishment carried out now can contribute to long-term climate change goals – and mitigate some of the impacts of climate change on building users.

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