I’d love a roof lantern in my new kitchen extension, but is it a huge mistake for temperature regulation? This is what the experts told me I should do

There is something so beautiful about light streaming into a room from above – it bounces off walls and surfaces, remains pretty consistent the whole day, and is somehow brighter and purer than that coming in from windows in the walls. And it is for this reason that I am desperate to incorporate a roof lantern into the design of the kitchen extension I have planned for next year.

The current space enjoys natural light from two conservation rooflights in the sloping section of the roof, along with a casement window and partially glazed stable door, which will be lost once we extend. I am hoping that there will be scope to include at least one area where it will be possible to fit a roof lantern, or some kind of glazed ceiling – both for additional natural light but also as a way of adding a little architectural interest.

My only reservation is the potential these kinds of features have for when it comes to temperature regulation. I have been in some houses where, in the height of summer, the sun beating on in through glazed areas of ceiling have made the spaces almost unbearably hot – certainly not something you want when working away in an already steamy kitchen. Come winter, I am concerned that a roof lantern could also contribute to the heat loss that our home already experiences. To help me decide, I reached out to some experts and put my questions on the matter to them – here's what they came back with.

Do roof lanterns cause issues with temperature regulation?

My worries about roof lanterns causing overheating stem from the homes of various friends I have visited where expanses of glass, be that in the form of roof lanterns or swathes of bifold or sliding doors, have resulted in internal spaces that feel very much like greenhouses in summer. While their houseplants might be thriving, these are definitely not rooms humans enjoy spending time in during a heatwave. But do roof lanterns always have to mean compromising comfort?

According to Charles Lowe, senior marketing executive at the IQ Glass Group, the main pitfall comes from not looking at the whole picture when choosing glazing. 'The biggest mistake is to think about the roof lantern in isolation. In a kitchen extension, you might have roof glazing, large sliding doors and fixed glazing all contributing to solar gain, while cooking itself also adds heat to the space. The glass specification, amount of glazing, ventilation and shading therefore need to work together.

'The best time to address all of this is before the structural opening and glazing specification are fixed,' adds Charles. 'For example, with a bespoke roof lantern or glazed extension, we would develop the roof glazing, solar control, opening elements and surrounding glass elevations as one coordinated package rather than treating overheating as a separate problem later.'

But while the heatwaves have subsided, at least until next summer, another factor that has been on my mind when considering whether or not a roof lantern is right for my kitchen extension, is whether or not it will make my house colder in winter. It is already freezing during the colder months thanks to a combination of poor insulation and draughty windows and doors.

Again this is something that can be accounted for during the specification process, by opting for a special coating that can help reduce heat loss, which means it won't feel chilly come winter.

Can the type of glass you choose for a roof lantern help prevent temperature issues?

I admit that I gave very little thought to the type of glass in our existing rooflights, but according to Edward Stobart, technical sales manager at IDSystems, when it comes to specifying a new roof lantern that doesn't turn my home into an oven come next summer, this is something I need to pay way more attention to. 'The important thing to consider is that, because the direct sunlight is coming from a higher angle, the risk of overheating is greater so the glass specification, especially on south-facing elevations, needs to be carefully considered.

'At IDSystems, all roof lanterns, rooflights and flat rooflights are manufactured with solar-control glass which features a microscopic coating that cuts out solar energy passing through the glass without reducing the light transmittance.'

Charles Lowe goes on to explain the importance of g-values when choosing glass for a roof lantern. 'Solar control coatings are incorporated within the insulated glass unit and their performance is measured by the g-value. The lower the g-value, the less solar energy passes through the glass. One commonly specified IQ Glass coating is a 70/35 specification, which allows approximately 70% visible light transmission while reducing the g-value to around 35%.

'For a high-end roof lantern, the specification can also combine solar control with low iron glass where particularly clear glass and neutral sky views are important,' adds Charles. 'These different requirements should be considered together rather than choosing the glass solely on appearance.'

On the other hand, in my battle against heat loss, Charles Lowe says that using Low-E glass could be the answer. 'It is important not to confuse solar control with thermal insulation. A Low-E coating helps reduce heat loss through the glazing during colder weather, while solar control reduces unwanted solar heat entering the building. Modern insulated glass units can incorporate both, helping a highly glazed extension remain more comfortable throughout the year.'

Edward Stobart

A long serving member of the IDSystems team, for the past 20 years Edward has advised and supported self-builders and renovators to identify the most suitable glazing options for their project. He has recently finished a complete renovation and remodel of his own home, transforming a tired 1960s house into a stylish modern family home. His expertise ensures that each project is equipped with cutting-edge, bespoke glazing designs that enhance both functionality and aesthetics.

Where is the best position for a roof lantern in an extension?

My kitchen extension faces south-east meaning that it gets the sun all morning and into the early part of the afternoon. If I were to go ahead and fit a roof lantern, it would sit right at the rear end of the extension – is that a wise move?

According to Edward Stobart, the orientation of my extension means I'll need to take extra care with the design of the lantern. 'The position and orientation of a roof lantern can make a significant difference to the level of risk from overheating. A large lantern on a south-facing elevation, with no shade from trees or neighbouring properties, will receive far more direct sunlight than a smaller lantern in a shaded spot on the north side of a house. The design of the lantern, and of the extension, needs to take this into account. Finding the right balance between the amount of glazing (including any windows and doors) based on this orientation should be a key consideration for the architect at the initial design stage.'

Charles Lowe goes on to explain that rather than rule out the idea of a roof lantern, I'll need to work with the designer closely to navigate the issue. 'We recommend involving the glazing specialist while the extension is still being designed. We can look at the amount of glass, orientation, solar exposure and required g-value before manufacturing the roof glazing, allowing the glass specification to be matched to the actual building rather than trying to solve overheating once the extension has been completed.'

Should my roof lantern open or include ventilation?

While opening windows doesn't necessarily help cool down a house in a heatwave, I know from experience that creating even a little cross breeze can. Hot air rises so I'm wondering, should my new roof lantern open in order to help alleviate any potential overheating issues?

'Preventing heat entering the room is only half of the equation – you also need a way of allowing excess heat to escape,' picks up Edward Stobart. 'Where possible, incorporating opening sections into a roof lantern can be extremely effective because warm air naturally rises. Thermostatically controlled roof vents are particularly useful because they can open automatically when the internal temperature reaches a certain level – but close again if it rains.'

Edward is also keen to point out that a holistic approach towards ventilation is helpful. 'It is important to think about ventilation across the whole extension. Opening roof vents combined with opening windows and sliding or bifold doors at a lower level can help create a natural flow of air through the space.'

Should roof lanterns be fitted with blinds to help regulate the temperature?

We all know how effective simply closing curtains and blinds can be when it comes to maintaining a comfortable temperature inside, when the world outside is experiencing extremes, but fitting blinds to a roof lantern sounds a bit complicated – plus, I'm wondering whether, if in order to have a roof lantern without any subsequent temperature issues I have to block out all the light, it is even worth it in the first place?

'With a complex or frameless glass lantern, conventional blinds can be more difficult to integrate because of the shape of the roof and absence of framing from which to support them,' explains Charles Lowe. 'In these situations, specifying the correct solar-control glass from the outset becomes even more important.

'Blinds can help to a certain degree, and there are specialist systems available for roof lanterns that sit within the reveal,' picks up Edward Stobart. 'They are useful for improving comfort, controlling glare and providing additional shade during the hottest parts of the day. It is important to note though that by the time the heat reaches the blind it is already in the room, so solar control glass is a far more effective method of preventing overheating because it stops the heat reaching the room in the first place.'

I'm still on the fence about whether or not a roof lantern is the best option. If, like me, you are looking for ways to bring more natural light into your home, make sure you look into all the options before making your final decision.