In this article, we’ll explore what each option will offer you in terms of design, lighting, price, size, ventilation insulation and cleaning so you can make a fully informed choice. 

Design 

Flat Glass Rooflight 

Flat roof windows are ideal for modern buildings as they have slim, clean lines and contemporary frames that match well with the rest of the building’s construction. They also offer the advantage of being rarely seen from the garden, and don’t obstruct upstairs windows, since they only have a 15cm upstand.  

If you want a more modern and sleek design the flat glass rooflights are ideal. These provide a clear view to the sky, with an unobstructed view to the outside. 

Lantern Rooflight 

Lantern rooflights can add an architectural element to the building. These products are popular among Victorian homeowners, as these larger constructions tend to align well with other elements of the building. Some things to be aware of when selecting roof lanterns are for example the height of a lantern in a single-storey flat roof extension, as you might have facade windows in the second floor of the existing main house, which could be partially blocked by the lantern.  

Lighting 

Flat Glass Rooflight 

Flat glass rooflights allow the maximum possible light into your home in clean, unbroken bands, so they are ideal for spaces that feel too small or dark. If you choose a flat glass rooflight that states that it is manufactured to internal dimensions, it will allow up to 25% more natural light to enter your room than other flat roof windows. The different shapes available allow you more flexibility in how the light is used within the space, with long, thin rooflights illuminating the space like a waterfall made of pure daylight and round windows creating interesting pools that shift across the space during the day. 

Lantern Rooflight 

Lanterns are usually standard dimensions; they offer a beautiful effect as the light is broken up and reflected by the lantern intersections. If your room is already quite well-lit and you’re looking for more daylight for artistic effect as opposed to just illumination, lanterns can make a great choice. 

Price 

Flat Glass Rooflights 

Flat glass rooflights are generally slightly cheaper per square metre for the same quality product, but the difference isn’t so huge that it would prohibit you from choosing a lantern if that is your heart’s desire. A hidden cost benefit of a good quality rooflight is its insulating properties which can actually save you money on your heating bills as a rooflight will potentially bring in more warmth from the sun than it lets escape from your home, even in winter. 

Lantern Rooflights 

As mentioned previously, the initial cost difference between the two styles isn’t huge. What is of more consideration is the installation and quality of the product. You will very rarely find a lantern rooflight which is pre-assembled. This means that the product will have to be assembled on-site by your installer. In turn, this tends to increase the installation time and thus the cost of installation. It is crucial to select a great installer, as the assembly on-site will determine the final quality of the product. 

Insulation 

Both lanterns and flat roof windows can be well insulated. Nevertheless, lanterns will often offer poorer insulation (indicated on the product description by a twice as high Uw value) due to the many joints between the glazing panes in the product. Every time you have connection between two pieces of glass there will be potential for heat loss. With a flat rooflight you only have the connection between the top unit and the upstand, which means that this option often delivers a much better insulating performance. When looking at insulation values, it is important to compare apples with apples. The Uw value indicates the insulation value of the entire product, whereas a Ug value only indicates the insulation value of the glass. You will see a much better Ug value or glass insulation property, than the Uw value i.e. the entire product's insulation potential. 

Ventilation  

There is little to choose between flat glass rooflights and roof lanterns when it comes to ventilation as both types can be opened to let out indoor pollution and fill your home with healthy fresh air, as well as having a cooling effect in summer.  

Size 

Flat Glass Rooflights 

An individual flat glass rooflight can go up to 4 square metres but individual units can be joined together to create a limitless expanse of sky. You also have more flexibility on the shape and distribution of flat glass rooflights. 

Lanterns 

Lanterns can be built bigger overall since you have smaller pieces of glass that are connected with plastic or aluminium frames. Roof lanterns can be up to 20 sqm. They typically follow a square or rectangular shape, although bespoke creations in different shapes are available, if your budget will stretch to that. 

Cleaning 

The glass on a lantern is more sloped which over time will mean that rain will clean and remove dust better. You will nevertheless have to clean the glass for both types a couple of times per year. A rooflight from Vario by VELUX is recommended to be installed with a pitch between 5-15 degrees, which also will allow the rooflight to be cleaned when raining. 

Interested in a large flat glass solution? 

Vario by VELUX offers a modular flat roof solution called the Unlimited Rooflight. This solution allows you to combine as many modules of up to 4 square metres as you want, which equals most lantern sizes. You could for example combine three modules of 3000mm x 1000mm, which equals 9 square meter of clear sky view. Each module will be connected with a minimalistic connecter system that measures only 126 mm. Furthermore, each module can either be fixed or vented, which will allow you to customise the rooflight completely for your needs. At the same time, the Unlimited One is very competitive in terms of pricing, which is why you should consider getting a quote and compare it to a lantern. The glazing in the Unlimited One comes in both double and triple layer, which allows our Uw value to go as low as 1.1 W/m2.K 

The most important thing is to capture as much daylight as you can though the roof, then comes ventilation and then insulation. So, remember to buy a high quality rooflight. Saving £200-500 on a bespoke rooflight or lantern is not worth it in the long run, when you consider that you will have a good quality rooflight in your home for 25-30 years.

Did you know Vario by VELUX rooflights, including the insulated glazing units, are supported by a 10-year guarantee?