top of page

Choosing Windows & Skylights

Updated: Nov 1, 2023

During the course of designing your extension you will have to choose some windows to provide light and ventilation. In fact you may have to choose several different types of window. Windows and/or doors to go in the walls, roof windows for any sloping ceilings and possibly skylights for any ceilings under flat roofs. There are of course lots of different manufacturers whose products can be specified but in general terms there are a few key decisions you ought to look at before choosing a supplier. He is a brief explanation:

1. Choosing Roof Windows for the Pitched Roof

There are various manufacturers of roof windows whose products each have their own technical merits. However, broadly speaking they are similar products and if you need to choose one my advice would be to decide first how you want the roof window to open and what type of glass you want to have in it. For example a roof window that is out of reach above a staircase is unlikely to be opened very often and will be difficult to clean. In this situation self cleaning glass would be advisable and so would a simple centre pivoting function as that is the easiest type to turn over and clean. However, if the roof window is inside a bedroom it will be easier to reach so cleaning becomes less of a challenge. In that case you could consider other types of opening mechanism. If you are tall and you have a long reach then you might prefer a roof window that is top hung because it will open right out to provide you with the best view. Conversely if you are short and have a short reach you may struggle to reach the handle of a top hung roof window to pull it back in (because the handle will be at the bottom of the sash and therefore right out of the roof when the window is open). In that case you will also benefit less from the bigger opening and so you would probably be better off with a pivoting roof window. These are the most common types of opening types:

Left image:

Centre Pivoting Roof Window (where the sash pivots right in the middle of the frame)

Middle image:

Top Third Pivoting Roof Window (the sash pivots higher up the frame to provide a bigger opening)

Right image:

Top Hung Roof Window (where the sash swings right out for the biggest possible opening)


2. Choosing Windows for the Walls

There are lots of windows which can be fitted into walls. However, most people choose to have windows similar in style to those already fitted into the rest of the house (unless of course they are planning to change all the windows). The main types of opening function are described below but there are also choices for materials, profiles, colours, handles and glazing.

Windows can be a point of weakness in terms of heat loss and noise transmittance and so it is always worth looking into the thermal efficiency of the unit including the glass, and considering the use of acoustic glass if you want to reduce noise.

Left image:

Casement Windows - where the sashes are hinged on the frame at the side.

Middle image:

Tilt and Turn Windows - where the sash opening has dual functions. It can be hinged to the side or at the bottom.

Right image:

Sash Windows - Where the sashes slide up or down one behind the other.


3. Choosing Skylights for a Flat Roof

Flat Roof Skylights come in all sorts of shapes and sizes. Facing directly towards the sky they will bring in a lot in daylight (though blinds can be bought). The most commonly used type of flat roof skylight is now the the flat glass panel type, which has largely replaced the use of polycarbonate domes. Polycarbonate domes are relatively cheap and almost impossible to break if anything should ever fall on them but they can have noticeable imperfections in them and they tend to be very noisy during heavy rainfall (especially the bigger ones). Glass on the other hand looks much more attractive and it is a bit quieter but it is by comparison quite expensive - costing on average 2-3 times as much as a similar plastic dome.

Left image: Glass Panel

Right image: Polycarbonate Dome

0 views0 comments

Recent Posts

See All


bottom of page