What Size Roof Lantern Do I Need?

Everything you need to consider when finding an appropriately sized roof lantern to bring daylight and character to your extension or refurb.

By Larry Bohan on 29 June 2018

korniche roof lantern in flat roof

What size roof lantern do I need for my room? It’s a question that our customers often ask us and one that cannot be answered definitively. There are, however, a number of questions you can ask yourself to help narrow down your search for the right size. 

Firstly though, let’s remind ourselves just why roof lanterns have become such a popular feature of modern home extensions and renovations.

What is so Special About Roof Lanterns?

korniche roof lantern in ground floor extension

Whether you have looked up and seen a glass lantern sat imperiously in a roof or only ever seen them on TV or in magazines, the visual appeal of roof lanterns is undeniable. However big or small, roof lanterns can enhance the look of a room both internally and externally, while making the area below feel more spacious.

These aesthetical factors alone are enough to convince some homeowners to add a glass lantern to their roof before the host of other benefits have even been taken into account.

Appearances aside, roof lanterns are an immensely popular choice thanks to an ability to let in three times as much sunlight as windows. This abundance of natural light not only brightens up larger surface areas, it also improves the overall energy efficiency of a property.

The thermal performance of a roof lantern is best gauged by the its U-value. REAL and Korniche lanterns have U-values of 1.2 and 1.5 W/m²K respectively.

Shop Korniche Lanterns Shop REAL Aluminium Lanterns

What Size Roof Lantern do I Need?

REAL aluminium roof lantern external kerb

To reiterate, this mostly comes down to personal preference, but your decision does need to factor in a number of aspects related to the size of your roof and the layout of the room below.

The most obvious thing to consider is the size of your new or existing roof. Externally speaking, it’s rare for a roof lantern to span the entirety of the roof. It’s quite common, though, to see roof lanterns installed in the centre of the roof, or close to it.

If you have seen a REAL or Korniche lantern on Sterlingbuild that you like the look of, feel free to send us an external shot of your current roof or a sketch of your plans so that we can recommend some ideal sizes.

A common misconception is that large lanterns are required to get the most from the sun and create that ‘stunning’ home feature. Neither is true. A smallish 100x100cm lantern can let in a surprising amount of sunlight, while a 150x250cm lantern gives an excellent area of light for a medium sized roof.

Generally speaking, we advise that the overall glazing area in any extension should cover atleast 15-20% of the overall floor space.

Excessively large roof lanterns can overwhelm the rest of the room, look out of proportion and come across as ostentatious. Equally, a roof lantern that is too small can look pointless and will not add much to the room. 

The most popular sizes we sell at Sterlingbuild are 100x150, 100x200, 150x250, 150x300cm.

As well as size, you should also consider what is, or will be going, directly below the lantern. It is this that will be most illuminated by the lantern and incoming sun. This might be a dining room table or a kitchen island.

Whatever it be, your lantern will be showing it off by shining a light on it. You might then, for example, want your lantern to span the length of the dining table, but at the same time run parallel with your bifold doors. This is why the lantern size and overall room layout are so closely intertwined.

Ideally your roof lantern will blend in effortlessly with the existing style of the property and interior décor so that it does not end up looking like a curiosity. It is for this reason that we sell roof lanterns which come with a healthy selection of colour options. With both Korniche lanterns and those from REAL, you can choose from black, white and grey interior/exterior combinations.

How Do I Measure for a Roof Lantern?

Two Korniche roof lanterns installed on roof external view

If you have browsed our roof lantern collection and are wondering what the sizes attached to each product relates to, it is the external kerb size (width x length), not the hole in the roof size. With most glass lanterns, this external timber upstand is required to be built on site by the customer as it does not normally come with the lantern. The eaves of the roof lantern sit flush on the upstand with a bit of an overhang for weathering. 

As required by Building Regulations, the external kerb should protrude at least 150mm from the roof to allow for adequate rain water runoff. 

For more information on measuring, visit our ‘How to measure for Windows, Doors & Rooflights’ blog, or speak to one of our friendly experienced sales team for further assistance.

What About Roof Lantern Cost?

real aluminium roof lantern rear home extension

Naturally, the bigger the lantern, the bigger the cost. Finding a standard sized roof lantern will keep these costs down compared to buying one on special order.

Using a made to measure service does, however, enable you to design your glass lantern to any size you desire, along with letting you customise a number of other features. If a bespoke lantern is something you want or need, send us your requirments via our bespoke form.

Should your search for a roof lantern be part of larger extension plans, purchasing your lantern alongside other extension components can sometimes come at a discounted rate. At Sterlingbuild, we will give you 5% off when you buy an aluminium lantern alongside a pair of bifold doors or sliders.

Though roof lanterns are one of the more expensive types of rooflight on the market, the many benefits that come with them make them a smart investment for many, whatever the size. Remember, your roof lantern will guarantee substantial savings on energy bills once installed, while adding significant value to your property for years to come.