Do Rooflights Have Energy Ratings (WER)? Decoding the Labels

Energy efficiency has become a defining factor in modern building design. Whether for new homes, extensions, or refurbishments, glazing choices are scrutinised not only for aesthetics and daylight but also for their impact on heat loss, overheating, and long-term energy costs. Most people are familiar with energy labels on appliances and, increasingly, on windows and doors. However, when it comes to rooflights, confusion often arises. Do rooflights have energy ratings? Can they be compared like windows? And how meaningful are the labels that sometimes accompany them? 

These questions sit at the heart of understanding window energy ratings rooflights. While energy ratings are well established for vertical windows, their application to rooflights and skylights is less straightforward. Differences in orientation, solar gain, and heat loss mean that rooflights behave very differently from standard windows, even when constructed from similar materials. 

This article explores whether rooflights have Window Energy Ratings (WER), explains how the system works, unpacks the meaning behind labels, and clarifies key concepts such as solar factor vs U-value. Along the way, we will look at how schemes such as BFRC rating skylights are interpreted, provide a clear rainbow label windows explained overview, and help you understand how to make informed decisions when specifying rooflights for energy-efficient buildings. 

What Are Window Energy Ratings (WER)? 

Window Energy Ratings, often abbreviated as WER, are a system used to assess the overall energy performance of a window. In the UK, the scheme is administered by the British Fenestration Rating Council (BFRC) and is designed to give consumers a simple, comparable rating similar to those used for household appliances. 

WERs take into account multiple aspects of window performance rather than focusing on a single metric. Instead of just measuring heat loss, the system balances heat lost through the window against useful solar heat gained through the glass. The result is a single rating, usually expressed as a letter from A++ (most efficient) to G (least efficient). 

For vertical windows, WERs have proven to be an effective communication tool. They allow homeowners and specifiers to compare products quickly and understand how a window contributes to overall energy use. However, applying the same system to electric roof windows is more complex. 

Do Rooflights Have Window Energy Ratings? 

The short answer is that rooflights do not always carry a traditional Window Energy Rating in the same way as vertical windows. While it is technically possible to calculate an energy rating for a rooflight, the standard WER methodology was originally developed for vertical glazing installed in walls. 

Rooflights differ fundamentally in how they interact with heat and sunlight. Their horizontal or near-horizontal orientation changes heat loss behaviour and significantly increases solar gain. This means that a rooflight assessed using the same assumptions as a vertical window may appear more or less efficient than it actually is in real-world use. 

As a result, many rooflights are not marketed with a standard WER label. Instead, manufacturers tend to focus on U-values, solar control data, and whole-unit thermal performance rather than a single headline energy rating. 

Why Orientation Matters for Energy Ratings 

Orientation is one of the key reasons why energy ratings are harder to apply consistently to rooflights. Vertical windows lose heat primarily through conduction and convection, with solar gain depending on orientation and shading. Rooflights, by contrast, lose more heat due to their exposure and gain more solar energy because they receive direct sunlight for longer periods. 

This difference has a major impact on how energy performance should be assessed. A rooflight with excellent insulation may still allow significant solar gain, which can be beneficial in winter but problematic in summer. The balance between heat loss and heat gain is therefore more sensitive in rooflights than in vertical windows. 

Because the WER system relies on standard assumptions about orientation and climate, applying it directly to rooflights can be misleading without additional context. 

Understanding the Rainbow Label: Windows Explained 

The familiar rainbow label associated with window energy ratings is designed to provide an at-a-glance indication of performance. When people search for rainbow label windows explained, they are usually referring to this BFRC-style label that grades windows from A++ to G. 

For vertical windows, the label reflects a calculated energy balance based on heat loss through the frame and glass, solar gain through the glazing, and air leakage. The colour scale makes it easy to compare products and identify high-performing options. 

When similar labels appear in connection with rooflights, it is important to understand how they have been derived. In some cases, the rating may be based on adapted calculations or assumptions that do not fully reflect horizontal installation. This does not make the data useless, but it does mean it should be interpreted carefully. Learn more about energy performance in rooflight glazing materials. 

BFRC Rating Skylights: How Does It Work? 

The idea of a BFRC rating skylights raises understandable questions. The BFRC scheme itself does not prohibit rating rooflights, but its core methodology is geared towards vertical windows. To apply a rating to a skylight, assumptions must be made about orientation, angle, and exposure. 

Some manufacturers choose to obtain BFRC-style ratings for rooflights to provide a familiar benchmark for consumers. Others avoid doing so, preferring to present detailed thermal and solar performance data instead. 

Where BFRC-style ratings are provided for skylights, they should be viewed as indicative rather than definitive. They can help compare similar products but should not be the sole basis for specification. 

Solar Factor vs U-Value: Understanding the Difference 

One of the most important concepts in rooflight energy performance is the relationship between solar factor vs U-value. These two metrics describe different aspects of how glazing behaves, and both are critical when assessing rooflights. 

The U-value measures heat loss. It indicates how quickly heat passes through the rooflight when there is a temperature difference between inside and outside. Lower U-values mean better insulation and reduced heat loss. 

The solar factor, often referred to as the g-value, measures how much solar energy passes through the glazing into the building. A higher solar factor means more solar heat gain. 

In vertical windows, balancing U-value and solar factor is relatively straightforward. In rooflights, the balance becomes more complex because solar exposure is greater. A rooflight with a low U-value but high solar factor may perform well in winter but contribute to overheating in summer. 

Energy ratings attempt to combine these effects into a single score, but this simplification can mask important details. Understanding both metrics individually is essential when specifying rooflights. 

Why Rooflights Are Often Specified by U-Value Alone 

Given the complexity of combining heat loss and solar gain, many rooflight manufacturers and specifiers focus primarily on U-values. This approach reflects regulatory requirements, which often set maximum allowable U-values for rooflights without requiring a full energy rating. 

While U-values do not tell the whole story, they provide a clear and consistent measure of insulation performance. For compliance and comparison purposes, this simplicity is often preferred. 

However, relying solely on U-values can overlook issues such as overheating risk and seasonal performance variation. This is why understanding the broader context of energy ratings remains valuable. 

Comparing Energy Metrics for Rooflights 

The table below illustrates how different energy performance metrics apply to rooflights and windows. 

This comparison highlights why no single number can fully describe rooflight performance. 

Interpreting Energy Labels as a Specifier or Homeowner 

For homeowners, energy labels are designed to simplify complex data. When dealing with rooflights, however, it is important to go beyond the headline rating. Asking how the rating was calculated, what assumptions were used, and how the rooflight will perform in your specific building context can prevent disappointment later. 

Specifiers and designers should treat energy ratings as one tool among many. Detailed thermal modelling, consideration of shading and ventilation, and an understanding of building use are all essential for effective rooflight specification. 

Regulations and the Role of Energy Ratings 

Building regulations in many regions focus on limiting heat loss through building elements. This is why U-values feature so prominently in compliance documentation. Energy ratings, while useful for consumer choice, are often secondary to regulatory metrics. 

That said, as energy standards tighten and whole-building performance becomes more important, there may be greater interest in more holistic ratings for rooflights in the future. 

Common Misconceptions About Rooflight Energy Ratings 

One common misconception is that a higher energy rating always means better performance. In the context of rooflights, this is not necessarily true. A rooflight that gains a lot of solar heat may score well in an energy balance calculation but still cause overheating. 

Another misconception is that the absence of a WER label means poor performance. Many high-quality rooflights do not carry a traditional energy rating simply because the metric is not ideally suited to their application. 

Choosing Energy-Efficient Rooflights 

Selecting an energy-efficient rooflight involves balancing insulation, solar control, and daylight requirements. Understanding how different metrics interact allows for more informed decisions. 

Rather than relying on a single label, consider how U-values, solar factor, orientation, and ventilation strategy work together in your specific project. 

Conclusion 

So, do rooflights have energy ratings? In some cases, yes, but not always in the same way as vertical windows. Understanding window energy ratings rooflights requires recognising the limitations of standard WER systems when applied to horizontal glazing. 

By decoding labels, understanding how the rainbow rating system works, and appreciating the balance between solar factor vs U-value, it becomes clear that energy performance in rooflights cannot be reduced to a single number. Concepts such as BFRC rating skylights can provide useful guidance, but they should be interpreted with care. 

Ultimately, energy-efficient rooflight specification depends on understanding how a product will perform in real-world conditions. Armed with the right knowledge, labels become a helpful reference rather than a source of confusion. 

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