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  • The benefits of installing rooflights or roof windows into your project are obvious: they can make dramatic improvements in key areas, including increasing the amount of natural daylight inside and improving ventilation around the home – most importantly in the kitchen or bathroom.

    The entire rooflights.com range is designed to be easily installed by tradesmen or DIY enthusiasts. However, to ensure a smooth process on site, we have listed below 5 ‘top tips’ to ensuring there are no hiccups on site when you come to installing your rooflight or roof window.


    Rooflights and roof windows come in an array of shapes and sizes, and its critical that you have the right dimension for your unit.

    When choosing a rooflight, all dimensions should be measured to the overall external upstand, including weathering – it’s important to pay attention to the corners where extra layers may have been applied to your roof finish. The roof light fits over the edge of the upstand/kerb (similar to a biscuit tin lid) and is manufactured with a tolerance to allow for small variations but extreme care should be taken when measuring.

    A roof window measurement is calculated based on the internal viewable width/span. For further information on this, and the different measurements required, please visit our technical drawings.


    With flat roof rooflight installation you should ensure that the product is not fitted completely flat itself. The inherent degree of flex in glass when it is installed ‘flat’ (compared to traditional windows which are installed vertically), is known as deflection and means that without even a slight pitch within the rooflight, rainwater will accumulate and begin to ‘pond’ on the glass.

    Installing the roof light with a minimum 3-degree pitch will avoid this but our recommendation would be to install at a 5-degree pitch for more efficient results and improved drainage.

    Unlike flat roof rooflights which are mounted onto an upstand, roof windows are installed in-plane, meaning they follow the pitch of the roof and are mounted flush with the surface. According to EN 14351-1:2006, roof windows should be installed on roofs with a pitch of at least 15 degrees and should be CE marked against this standard.


    For a flat roof installation, it is critical that you meet all current regulations and good building practise. Most rooflights are designed to be fixed on to a ‘builder’s kerb’ detail which sits up from the supporting flat roof assembly at the point of your aperture. This ‘builder’s kerb’ is called an upstand and allows the external surfacing to lap up and form a weather-tight seal.

    An upstand helps to protect the property and ensures the waterproofing does its job. The rooflight can then be fixed on to the upstand to weather proof the aperture within the flat roof.

    The requirement for flat roof upstands is set out in the British Standard BS 6229:2018 Flat roofs with continuously supported flexible waterproof coverings. “This standard recommends a clear upstand of at least 150mm above the finished roof surface, including any paving, inverted insulation or green roofing.”


    Deliveries of rooflights and roof windows will generally be delivered roadside or ‘kerbside’. You will be required to move the product from the delivery vehicle and to the point of installation on the roof.

    It is important that you take note of the product weight and ensure that you have enough people on site, or the suitable equipment to lift the unit/s – careful planning must be performed to avoid any damage or injury. Consideration may be required regarding additional costs that you may incur for the hire of lifting equipment if you have bulky units, or for hard to access locations.

    Due to vehicle sizes used, companies may not be able to deliver to locations with restricted or narrow access, and it is best to speak to the supplier beforehand if you are unsure.


    Most rooflights and roof windows come with an installation guide that will cover a step by step guide to installing your rooflight. It is important to follow these individual instructions carefully, as it could impact the installation process and how the roof window or roof light performs.

    Be sure to check you have the right tools, these are sometimes supplied with the product – the rooflights.com fixed rooflights come with a hardware kit with all the necessary parts needed. Depending on the manufacturer, special drill bits may be required – for example, if you’re installing Velux windows you will require a screw that uses a T20 drill bit. This is commonly used for day-to-day work on building sites.

    Here at rooflights.com, our technical support team is ready to provide any assistance you require, whether that’s pre-purchase, pre-installation or during the installation itself. We also offer a variety of resources to help guide you with the installation of your rooflight or roof window – such as helpful step-by-step videos.