How Do I Calculate VELUX Window Size for an Extension?

When you’re building an extension you’ll need to think about windows. There are many different factors that might affect how much glazing you’ll need and where you should place it. Before you finish designing your extension you should work out what the window situation is going to be so you can take that into account. 

Calculating VELUX Window Size

Firstly, you should establish your floorspace. The recommended minimum level of glazing by VELUX is 20% of an area’s floorspace, so this makes a good starting point. Remember if you adjust your floorspace later in the planning that the glazing level should be altered as well. This metric of 20% allows for a large percentage of daylight, which has many positive health effects. Too much below this can lead to a very oppressive atmosphere. 

Now you need to find the windows that would be right for your extension’s roof. Anything below a pitch of ten degrees is classified as a flat roof, while anything above that is a pitched roof. Different windows are made for both types. Getting the right type of window for your roof is as important as getting the right size. 

Placing your Windows

In addition, there are other factors that can be important in terms of windows. For example, which direction does your extension face towards? If it’s primarily towards the north you may want to increase the amount of glazing you have to compensate for less sun exposure. If you have a high-pitched roof and there are obstructions like trees or another house you may have to place your windows in a specific spot so your room can still get light.

You also have to choose between bundling your windows or having them spread apart. Clustering them together might be necessary based on what furniture you have. However, if you’re looking to maximise airflow and efficient light coverage, windows should be spaced out.