The Benefit of Experience – Roof Window Considerations

There are more roof window manufacturers than ever in the UK today.

Below are some of the key considerations you should be thinking about when specifying a roof window.


Manufacturers must be able to declare a whole unit (Uw) value for their roof windows. Being aware of what companies are promoting will ensure you are comparing the right type of information. Any pitched roof window manufacturer is required by law to CE mark their roof windows. If a manufacturer is unable to provide this information it is recommended that you speak with other companies who can provide it.

Humidity Levels

It is imperative that at the point of specification you let the manufacturer know where the roof window is going to be installed. Manufacturers should be able to provide you with the minimum temperature factor which will allow you to analyse the risk of condensation as well as compare the condensation potential from different roof window providers. Having a roof window that is made from steel does not mean the roof window will be prone to condensation. It is a combination of the humidity level and temperature of the room which dictates the dew point.

Window Loads

Window load requirements can vary by region – for example, roof windows installed in the North of Scotland are at a far greater risk of a heavy snow load than those installed in the Southern counties. You should always check which size the load testing has been carried out on as it must be the largest standard size; as wind loading test data can only be applied to the tested window size or smaller. If you have any doubts then the roof window manufacturer should be able to offer support for specific project calculations.

Client Operation

One of the most overlooked aspects of roof window specification is how the end-user is going to use it. For example, if the roof window is specified as fixed shut can it be made openable in the future? How has the manual opening distances been calculated? Is it in line with British Standard BS8213-1:2004 which looks at the safe opening distance for windows, doors and rooflights? All of these should be considered at the point of specification to avoid further costs to the end-user after hand over of the scheme.

Specifying rooflights is not something that should be taken lightly. Whilst the above points are not an exhaustive list of considerations, we believe they are some of the key things you should be looking at. If you would like to request a copy of our full considerations guide, email to and we will be happy to email you a PDF.

Latest from Our Blog