At Whitesales, we pride ourselves on delivering high-performance rooflight solutions that not only maximise natural daylight but also contribute to energy efficiency and building performance. One of the most critical factors in evaluating a rooflight’s thermal efficiency is its U-value, but what exactly does this mean, and why does it matter?

In this guide, we’ll explain U-values, their importance in modern building regulations, and how we ensure our products meet and exceed industry standards.

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What is a U-value?

A U-value measures how effectively a building component, such as a rooflight, conducts heat. It is expressed in watts per square metre per degree Kelvin (W/m²K). In simple terms, the lower the U-value, the better the insulation – meaning less heat escapes from inside a building.

For example, an uninsulated cavity wall can have a U-value of around 1.5 W/m²K, whereas a well-insulated rooflight can achieve values as low as 0.65 W/m²K. The lower the number, the greater the energy efficiency and the lower the heating and cooling costs.

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Why do U-values matter for rooflights?

Rooflights are an essential feature in many buildings, providing valuable daylight and reducing the need for artificial lighting. However, they also represent a potential point of heat loss if not properly designed and manufactured. Choosing rooflights with low U-values ensures that buildings remain energy efficient and comply with stringent building regulations.

Building regulations in the UK set specific maximum U-values for different elements of a building. According to Approved Document L(England), the maximum permissible U-value for rooflights in new and existing buildings is 2.2 W/m²K. However, at Whitesales, we aim to provide products that significantly outperform these minimum requirements, helping our clients create more sustainable and energy-efficient spaces.

How are rooflight U-values calculated?

The thermal performance of a rooflight isn’t measured in the same way as walls or windows. Instead, it is calculated based on the “developed area” of the rooflight, also known as the Ur-value (for rooflights only) or Urc-value (for rooflight and upstand assemblies).

This developed area includes the entire external surface area of the rooflight, as opposed to just the glazing or the opening it covers. This approach aligns with British and European standards, ensuring that U-values reflect real-world performance.

Key factors affecting rooflight U-values include:

·       Glazing type – Double, triple, or insulated glazing can significantly impact thermal performance.

·       Frame material – Thermally broken aluminium frames help minimise heat transfer.

·       Upstand insulation – The upstand (curb) supporting the rooflight can influence overall heat loss, which is why we ensure our assemblies are optimised for insulation.

The Whitesales approach to energy efficiency

At Whitesales, our commitment to quality ensures that all our rooflights are designed to deliver exceptional thermal performance. We carefully engineer our products to achieve the best possible balance between insulation, daylight transmission, and durability.

Our rooflights are available with a variety of glazing options, including:

·       Double or triple glazing for enhanced insulation

·       Low-emissivity (Low-E) coatings to reduce heat loss

·       Argon-filled cavities between glazing layers to improve thermal efficiency

As mentioned, the upstand plays a crucial role in the overall thermal performance of a rooflight. At Whitesales, we supply factory-insulated upstands that meet the highest industry standards, ensuring that the entire assembly delivers the lowest possible U-values.

We also ensure that all our products comply with or exceed the latest regulations, including:

·       Approved Document L (England & Wales)

·       Section 6 (Scotland)

·       Part F (Northern Ireland)

By consistently testing and refining our designs, we provide solutions that not only meet compliance requirements but also contribute to lower energy costs for our customers.

Making the right choice for your project

Selecting the right rooflight for your project involves balancing aesthetics, daylighting, and thermal performance. At Whitesales, we make this decision easier by offering expert guidance and high-quality solutions tailored to your specific needs.

If you're looking for rooflights that provide superior insulation and energy efficiency, our team is ready to help. Contact us today to learn more about how our products can enhance your building’s performance while meeting the highest industry standards.