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Skylight Selection

The right skylight for the right application

There are two main varieties of skylight available to customers, each offering different attributes and different features. These varieties are the Specular Skylight, and the Roof Window.


The Specular Skylight (also called a ‘Flexible Shaft Skylight’) consists of a domed roof assembly with a reflective shaft, which is concealed inside the roof cavity.


 At ceiling level this skylight is comprised of a square or circular frame housing a diffuser to soften and distribute light.



These products are often added to existing buildings or structures to provide light for dull areas. HandiLites and SupaLites are examples of Specular Skylights.


The Roof Window is literally a window in the roof. These are usually installed at the time of

construction or during renovations; although they can also be retrospectively fitted. Installation of these fixtures requires the involvement of tradesmen as the shaft for the window will need to be framed out and plastered. Roof Windows can be opening windows or fixed windows depending on the needs of the customer.


Consider the look you are hoping to achieve in your home. Flexible Shaft Skylights are extremely functional while remaining unobtrusive to the eye. Roof Windows can create a real feature in any home by offering a new and dramatic vista of the outside world. Opening windows also offer ventilation and air circulation to enhance your home’s feel as well as look.


Another factor to take into account when choosing the skylight that is right for you is the size of the area to be illuminated. Like any window the primary function of a skylight is to transmit the ambient light from outside your home to inside your home. The larger the room, the larger the skylight needs to be. You wouldn’t put one tiny window in the wall of a large family room and expect the room to be filled with light. The same principle applies  here.


Also take into account your furnishings and décor. Rooms with dark walls or furniture often need more light to brighten them up. You may find that going up an extra size for a room with darker décor is a wise move.

Length of Shaft

Another factor for your consideration is the distance between the roof and the ceiling. The greater the distance the light must travel, the more the integrity of the light that reaches ceiling level may be compromised. While this is not a large problem with Roof Windows it is far more crucial with Flexible Shaft Skylights. Our Skylights are supplied standard with 2 metres of shaft. This is because we have found that this is the optimal length of  shaft to maximize the light transmission.



However, there will be occasions when 2 metres of shaft is insufficient to bridge the ceiling cavity and greater lengths of shaft will be required. Remember, the further the light is required to travel down the shaft the more the intensity of the light which reaches the room below is reduced. Imagine looking down a long tunnel, while it may be very bright at the other end of the tunnel very little of that light will reach your end of the tunnel. The principle is the same. This can be overcome by increasing the size of the skylight. This will allow more light to enter the skylight and thus more light to reach the room below. We would suggest that you increase the size of the skylight by a factor of 100mm for every metre, or part thereof, of additional shaft you need to  attach.

What's in the roof?

Consider also, the contents of you ceiling cavity. Electrical wiring, air conditioning and heating ducting, even water pipes inside the ceiling can all interfere with the size or placement of a skylight. Always take the time to conduct a quick inspection of the site before deciding on the size or shape of your skylight. Some of these fittings may not be easily relocated.

Skylight Selection Size Chart

The right skylight makes all the difference

ACOL Skylights & Roof Windows © 2018