What are the differences between Skylights, Roof Windows, and Velux Windows?

These terms have been known to confuse, bewilder, and otherwise confuddle anybody who hears these terms in unison; but have no fear for JCM Roofers are here. Have a read through this trusty article to hopefully help clear things up (pun intended).

Firstly, Google will often have a particular definition for each of these words, but you should trust the experts instead. To summarise, they are all windows but they do have slightly different functions. Now let’s elaborate:


A skylight is a type of roof window which allows transmission of light for utilising the benefits of natural daylight (and the sky of the night, I suppose). Skylights go all the way back to Roman architecture. But then, in the middle of the 20th century, they evolved quite a bit. These changes, such as energy conservation, lights transmission, and roof design, were a result of the newly gained popularity and usabilty of skylights

The types of skylights include:

  • Fixed-unit skylights: Made of glass or plastic and does not allow ventilation.
  • Open skylight: Structural frame without glass or plastic, but has one hole with which through air can travel.
  • Operable skylight: Also known as a “roof window”, and can be opened and shut as is typical of a window.
  • Retractable skylight: Similar to the operable skylight, except rolls on or off a track. This means the glass can go all of the way off of the frame allowing the window to open fully, as opposed to the operable skylight which only allows a half opening due to it’s hinge.
  • Tubular skylight (TDD): A roof-mounted dome which was designed to draw in sunlight and negate UV rays. Its refracts the sun and enhances daylight and is common in otherwise windowless rooms.

Roof Windows

A roof window, similar to one of the types of skylights, is a window designed and made for the roof. It allows open air and light to enter the inside of the room. It is usually bigger than a skylight, as so is used to enjoy the view of the sky. These windows do however have a side function of insulating from noise pollution.

A roof window brings in daylight and fresh air, and are manufactured in such a way that you can be sure of their durability. They need to be able to withstand any changes in weather conditions from wind to rain, from snow to searing sunlight. They can endure any climatic conditions, regardless of where in the world they’re installed.

Velux Windows

The Velux brand completely revolutionised the skylight and roof window game. Pioneering the roof window industry, the Velux group has been in the commercial niche since before the mid 20th century. They are the Dyson of the skylight industry.

Mr Villium Kann Rasmussen, a man of Danish nationality, patented his invention in 1942. The VE in VELUX stands for ventilation, and the LUX for light. These windows are specialised glass roofs, with the objective of illuminating dark attics with fresh air and daylight. Today, Velux is international.

All Velux windows are thermally efficient, and perfect for lighting stairwells, hallways, bedrooms, bathrooms, and any dark space which would benefit from increased light or view of the sky.

JCM Roofers Oxford
65 Oliver Road

Phone: 01865920244

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