Need help?


The sky’s the limit! If you can dream it, we can build it!

Call US:0800 999 7774

What Is a Rooflight U-Value


A U-Value is a commonly thrown around term in the glazing world, but often our customers don't understand what this it means. This blog is here to help, as it will answer what a U-value is, what to look for when evaluating U-values and how Rooflight Solutions rooflights have high-quality glazing to meet your U-value needs!


A U-value, also known as thermal transmittance, is the rate of transfer of heat through a material (or in this case, glass), divided by the difference in temperature either side of that material. Or, as described Wikipedia, "the transfer of heat (in watts) through 1 square metre of glass divided by the difference in temperature across the structure."

Meaning, it is a measure of how good a material is at preventing heat from travelling through it, so the lower the U-value, the better.

Many different materials and coatings have different U-values, meaning when it comes to designing a structure, you want to utilise the potential of these materials to best reach your desired needs and thermal goals.

The U-value is, therefore, a great place to start when comparing different rooflight products, as it is a basic indication of how well a material insulates a space.

Don't be fooled, as just because a product has a lower U-value, it might not be better, as a high-quality double-glazed product might have a higher U-value than a low-quality triple-glazed product!


A common question that we get asked about Rooflight Solutions rooflights is whether the U-value changes. Often, manufacturers will measure the U-value of a rooflight in controlled conditions within a factory, however, post-construction measurements are much more useful as they have the advantage of accounting for workmanship.

This means that actual U-values may be lower on sight that advertised, due to poor workmanship in installing the rooflight into your roof. To counteract this, Rooflight Solutions recommends you use our qualified and highly trained workmen who can guarantee the closest to the theoretical U-value as possible.

In general, the U-value will slightly decrease over time due to degradation of the connections within the rooflight and connections, but this is natural and with our 10-year Rooflight Solutions Warranty on all of our products, you have absolutely nothing to worry about!


When it comes to getting the best value out of both your rooflight and installation quality, you want to be looking for whole-unit U-values instead of just centre pane U-values. As mentioned above, when installed on-site, there are many considerations such as around edge seals and installation quality which might impact the centre pan U-value, so having that whole-unit value will give you that holistic view of the product.

All of Rooflight Solutions centre pane U-values can be found on the product descriptions of each product. To find out the centre pane U-values of our products for your specific fitting requirement, feel free to get in touch using 0800 999 7774 or sales@rooflightsolutions.co.uk.

Whole-unit U-values are often much better at painting the picture of how efficient a rooflight is at keeping your house insulated when installed. Don't be fooled when suppliers quote a centre pane value and claim it is higher performing than a Rooflight Solutions product as:

  1. This is not in compliance with building regulations
  2. Like-for-like products from other suppliers will not beat Rooflight solutions cost or quality

Over time, a lower U-value will give you the best value for money typically, as you will save money through being more energy efficient and losing less heat through your glazing.


If this blog hasn't answered all of the burning questions you had about U-values, then the Rooflight Solutions team has put together a resource list for you to use to learn more!

We hope you enjoy learning more about U-values! Fancy learning more about rooflight trends in 2020? Check out this blog to find out more!


The U-value of a rooflight is one of the most important properties to consider when choosing a supplier and rooflight that fits your needs. Custom bespoke designs from Rooflight Solutions allows the exact needs of your building to be met.

Working with Rooflight Solutions for your rooflight needs gives you:

  • Nationwide delivery
  • Unbeatable prices
  • Domestic and commercial supply options
  • 24-hour service
  • In-house UK manufacturing

Improve the life and look of your space by working through Rooflight Solutions for your rooflight needs.

Have any more questions about U-values or Rooflight Solutions products? Feel free to get in touch with one of our friendly team through 0800 999 7774 or sales@rooflightsolutions.co.uk and we will do our best to answer any burning questions you may have!

Reset your password