Natural Light - Rooflights

Roof lights explained

Natural light is one of the most desirable and valued qualities in the home. When embarking on a building project, increasing the amount of natural light in the home is often top of the list for BTL customers for several reasons:

  • Natural light helps transform darker areas of a property and creates an illusion of space that optimises any living space.
  • Allowing more natural light into the home means less reliance on gas/electricity, reducing the cost of energy bills and saving the home owner money as a result.
  • Research shows that there are a number of health benefits associated with exposure to natural light including: an increase in serotonin levels, vitamin D and regulation of the body's natural cycles.

One of the most effective ways of getting more natural light into the home can be achieved by installing of roof lights. Studies conclude that roof lights can be up to three times more effective than vertical windows at emitting light.

This design feature has increased in popularity over the years and manufacturers are providing a number of options for those wanting flat roof extensions, side returns and loft conversions. Here at BTL there are several things that we must consider when specifying our customers with the most appropriate roof light for their project.

There are several different types of roof light to choose from and most manufacturers will cater to the needs of any project. However, the number of options available can often make finding the right roof light a confusing task.


Fixed, opening and walk-on are the 3 most common types of roof light that we specify here at BTL.

Fixed roof lights cannot be opened and serve the sole function of bringing light into a space. These can be a single unit or several single units joined together creating a modular construction designed to reduce the size of the frame around the glazing itself. If a larger roof light is required, modular units are easier to transport and install compared to large single units which often need costly plant equipment to lift into position.


Opening roof lights serve the same function as fixed models but also allow for added ventilation. This can help maintain air flow and control temperature during the warmer months, especially in loft conversions. Most manufacturers can supply manual or electrical opening mechanisms but the latter will increase the cost.


Walk-on roof lights are common in basement and roof terrace conversions and allow light into areas that would commonly cut off from natural light. They can be used internally as well as externally and provide a solid walk-on structure that fits flush with the surrounding roof/floor finish, allowing light to penetrate between floors that would otherwise be closed in.

Cost will also influence the style and specification of a roof light. The easiest way to break down the difference in cost is to distinguish between stock options and bespoke. Most manufacturers will offer several off the shelf stock sizes in all three of the options specified above. These often have the shortest lead times and are the cheaper option.

Bespoke sizes must be made to measure which increases the lead time and cost considerably. However, this option allows the designer more flexibility in overcoming complicated design issues, resulting in a unique solution for the customer.


The size of roof light also dictates the cost in terms of supply and installation. The larger the unit the greater the cost is to supply the unit. Transportation and installation costs will also increase with the size of the roof light as specialist lifting equipment must be used for units over a certain weight. In some cases, traffic management systems and council permits will have to be acquired to do this which can be costly and time consuming in London.

Building Regulations
As with many elements of build project, Building Regulations must be adhered to at all times. Within the Government's 'approved documents' there are a number of requirements that must be met when installing roof lights. Most manufacturers' products will meet these but it is important to note the following

1.Energy efficiency is measured in terms of heat loss through the glazing and frame. This must comply with the recommended U-value and not be exceeded. U-values measure thermal conductivity and are based on the specification of the glass and frame.


2.Solar heat gain must also be considered especially if the windows are south facing and are exposed to direct sunlight for long durations. Most companies supply solar control glazing that restricts solar gain and limits exposure to UV rays.



3.Structure is also something that must comply with building regulations when altering an existing roof as well as a new structure as extra support is needed to take the load of the roof light. This is achieved by doubling-up the the existing rafters to strengthen the opening.



The above information covers the main points that we take into consider here at BTL when specifying roof lights for our customers' projects. For more information on roof light design, specifications and suppliers, please see the links below.

If you have any questions relating to this article, why not ask our Build team?

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