Size matters when it comes to roof lanterns. The size of the roof lantern is important to ensure you have enough light in the room and create a bigger space, especially in living rooms.

Various factors contribute to the size of your roof lantern, such as the roof’s structure, position, and where the room faces.

How To Go About Choosing the Correct Roof Lantern Size

Picking the correct size for your roof lantern depends on your taste, but it is also influenced by what you’re working with. You would usually see roof lanterns installed in the middle of the room, but a flat roof accommodates installation in any area.

Let’s look at the factors that determine the size of your roof light.

Which way is the room facing?

The direction your room faces greatly affects the size of roof lanterns. For example, north-facing roof lanterns will only get sun in the morning, whereas south-facing roof lanterns usually get sunlight during the day, so sizing should balance daylight with energy efficiency for better comfort and thermal control.

This means the north-facing room would benefit from a larger roof lantern. Have a look at our other blog to answer the question: does a roof lantern let in more light?

Practicality

When thinking about the planning permission, also consider your privacy. Some plans may be rejected if your roof lantern exposes too much of your home. On the other hand, you don’t want the roof lantern to be too big that it can be peered into if your home is overlooked. You just may be letting in more than just natural light!

Structure of your home

If you have an old house, it may not be strong enough to hold a big roof lantern. You must evaluate your existing roof structure, check for rafters and other obstructions, and rule out structural issues before determining the size of roof lights you need. This helps greatly.

If you’re thinking ahead, work out how the roof lantern will increase your house’s value. A well-placed and right size roof lantern can elevate your house spec significantly.

What is below the roof lantern?

You should also consider what will go straight below the roof lantern, as it will be exposed to direct sunlight. This is often a kitchen counter, kitchen island or dining table. No matter what it is, the roof lantern will place a lot of attention to it, so deciding on the size is important.

For example, you may want your roof lantern to be big enough to run parallel with the bifold doors, and this will allow your roof lantern to blend in effortlessly with the style of the room and enhance the space.

When judging whether a large or small roof lantern will look balanced, consider the room layout. Large roof lanterns can be overwhelming, look out of proportion if it is a small room, and look flashy instead of classy. However, a small roof lantern can be easily forgotten and even pointless in a large space.

How To Measure for a Roof Lantern

If you have looked at our different types of roof lanterns and are now asking, "what size roof lantern do I need"? Don't worry: we have you covered. The measurements of our roof lanterns are the external kerb size, so the roof opening itself must be measured correctly, not just the gap, and the internal dimensions should match the product specification for a perfect fit.

Taking the correct measurements of your roof is essential when deciding on the size of your glass roof lantern. For accurate measurements on site, use a tape measure when measuring the opening, and give us the width x length of the area, also allowing for the overall width where the lantern sits on a timber upstand.

Measure the width and length in multiple places and note any variation.

Verify that the opening is square by measuring from corner to corner, and double check the figures for a snug fit.

Our advice is to compensate for an upstand of 150mm tall and 100mm wide, with the width being in the measurements you give us. The edges of the roof lantern must sit properly on this upstand, with some overhang for adequate rainwater runoff and weathering.

The external kerb must stick out 150mm from the roof for this as well, and the external upstand size should include the frame footprint rather than just the hole. You can find more hints and tips here.

Allow for the thickness of any roofing membrane or waterproof membrane, as well as insulation, to prevent water ingress and potential leaks.

What Types of Glass Lanterns Are Available?

Not only will the type of glass play a role in the comfort of the room, but it also affects the size of the lantern.

You can use toughened glass on the outside and laminated glass on the inside, which can accommodate most sizes of roof lanterns.

The outside glass is very strong, and laminated glass can still hold together if broken - a vital safety feature. You can also expect a soft-coat low-emissivity coating, argon gas fill, and warm edge spacer bars.

You can also glaze your glass to improve insulation, with the u value varying between glazing choices and affecting thermal performance. High-specification, double-glazed or triple-glazed lanterns can be quite costly, so you have to be sure of your size before purchasing.

Most glass lanterns these days offer the options of solar control and self-cleaning glass. You can get these together or separately. Visit our website to learn about the types we offer.

Is A Lantern Roof Worth It?

With the correct size, a roof lantern can transform a room and add value to your home. They complement anything set below it, whether it is a dining room, aluminium door, or windows.

Lanterns are popular with homeowners for the following reasons:

• The perfect roof lantern can improve the room’s appearance and comfort while making it feel brighter and bigger.

• It alters the room dimensions and increases the roof height.

• It is aesthetic and a unique way to add natural light to your home, which increases its value.

• Lanterns are energy-efficient, retain heat, and save money on energy bills.

FAQs

What size roof lantern for a 6 x 4 room?

Typically, a 150x250 x 100 cm roof lantern lets the sunlight in at a very low density, while a 150x250 x 200cm lantern offers optimum illumination for medium roofs.

It is generally suggested for extensions based on a size of three to five per cent of the total surface area.

What are the common roof lantern sizes?

They are available in standard sizes, from compact options such as 1000mm x 1000mm up to larger formats like 2000mm x 4000mm, alongside many choices in styles, shapes, and colours. For a korniche roof lantern, standard sizes commonly range from 1000mm to 4000mm, while bespoke sizes and custom sizes may be available for non-standard openings.

How much is a roof lantern?

A new roof lantern cost varies depending on the size, glazing, and glass type. The prices can range from £800 to just over £2000. Visit our website or speak to our team for further information on pricing and price matching.

Do I need planning permissions for installing a roof lantern?

Usually, you wouldn’t need planning permission. A lantern is permitted if you adhere to the conditions such as:

• It must not stick out more than 150mm from the roof.

• It is not higher than the highest point of your house.

• It has a side-facing window that is murkily glazed, with openings 1.7m above the roof floor.

If there is any doubt about the roof pitch or whether necessary adjustments are needed, consult a professional before installation.

This applies to average UK houses; however, converted houses, flats, and maisonettes may differ. You should look into the building regulations in these cases.