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A Guide to Roof Window Installation


12th July 2018

Once you understand how to install roof windows, you can start to adapt areas of your home that require more daylight and ventilation. Depending on your DIY experience and the complexity of the job you may require a professional firm to install the window(s) on your property.

However, doing your research on how the process works and the best materials to purchase will enable you to manage your budget and ensure the job is completed to a high standard. This article will discuss everything you need to know about how to install a roof window, including a step-by-step overview and a full list of tools required for the project.

What is the Process for Fitting a Roof Window?

We would always recommend contacting a professional fitter to complete a roof window insulation, however, if you're confident enough to proceed yourself - ensure you follow these steps.

Roof Window Installation - Roof Stores
Roof Window Installation

  1. Make a mark on the rafters where you would like to position the roof window. Identify the centre of the window before removing an area of felt or boarding that will then expose the slate or tile roofing.
  2. The first slate or tile can be removed by pulling it back between the rafters. You should also ensure space below where you are working is cordoned off and that you also have something stable to stand on.
  3. To create a good enough opening for access, continue to remove the slates or tiles, before cutting the battens close to the rafters.
  4. You may need to also cut a rafter at both the top and bottom before removing it along with the battens to create a wide enough opening.
  5. At least one extra row of slates or tiles on each side will need to be removed beyond the required width to accommodate the window flashing. Make note of the overall height before marking both the top and bottom on the rafters. Use a 90° square to ensure the window fits correctly.
  6. To create a clear aperture, cut out the rafters before measuring both the width and height and checking how square it is. The trimmer positions and infill rafters need to be marked and the lower trimmer inserted and nailed in securely. You can then do the same with the top trimmer if needed.
  7. Ensure everything is nailed securely and that all the surfaces are flush along with the opening being square.
  8. Remove the window sash from the frame by firmly holding the window in an upright position. Next, the handle can be unlatched, and the window partly opened, and any wooden packing blocks disposed of. Using a screwdriver loosen the clips and then remove the cover. Firmly hold the window sash keeping the black arms clear and carefully lift it from the pivot slots.
  9. A metal dowel bracket can be inserted into the four corner holes in the frame. These can be lightly tapped into place using either a hammer or rubber mallet. Ensure the brackets remain square to the frame and hammer into the spiked end.
  10. Position the window frame into the opening on the roof and ensure the metal pins are sitting on both the top and bottom battens. Once you are happy it is sitting squarely in place, either drill or nail into a slot in each bracket. After checking the window is square and level, you can drive the nail in.
  11. Now it’s time for weatherproofing. Begin by inserting the flashing pieces, focusing on the lower one first. The black rubber trim should be lifted and tightly positioned beneath the rubber up against the frame. Take note of the flashing instructions as they do differ on either tile or slate roofs.
  12. The slates or tiles can now be replaced around the sides of the window. An electric angle grinder is the best tool to use to cut through slates or tiles, or alternatively use a tile cropper while wearing gloves and goggles for eye protection.
  13. The sash and the top sash cover are next to be refitted. Firmly hold the window sash at the top and bottom to move it through the window, remembering it needs to be both upside-down and back-to-front.
  14. Adjust the window while holding it to ensure the two pivot mechanisms fall into the channel slots in the frame. The arms will have to be re-attached at the top of the frame, before pushing the clips firmly back into place. The top sash cover can be re-attached, and before releasing the window, check everything is securely in place.
  15. If you find the sash is not completely in-square this can be adjusted on the left-hand side by using the alum key that came with the fixing packs.
  16. If you're still unsure, get in touch with at least three licensed fitters for quotes and ensure you check their feedback - it's better to pay a bit more than being lumbered with problems further down the line.

How Do I Measure the Correct Area for a Roof Window?

To ensure the installation of the roof light goes smoothly, you will need to get the measurements of the window correct.

The size of the roof opening is the most important measurement to take note of so enough space is created for the window to open and close without issue. This will dictate the size of the hole you need to make in the roof before installation.

Roof Window Installation - Roof Stores
Roof Window Installation

For roof lights on flat roofs, you will also need a timber upstand, which is usually created using 2” timber. Whether you are building your own or using a pre-made product this also must be factored into the dimensions.

What is Required to Fit a Roof Window?

As with any alterations made to a house you need to make sure you have the right tools to hand to get the job done correctly. When it comes to fitting a roof window, the following items should cover everything you need:

  • Tape Measure
  • Hammer
  • Work Gloves
  • Screwdriver
  • Square
  • Pencils
  • Angle Grinder
  • Pincers
  • Panel Saw
  • Craft Knife
  • Safety Goggles
  • Window Fitting Instructions
  • Polyurethane Caulk
  • Drill
  • Tin Shears
  • Crowbar
  • Reciprocating Saw
  • Circular Saw
  • Extension ladder
  • Extension Cord

Which Type of Roof Light Solution Should I Choose?

This will depend on the type of roof and property that the roof light is being installed into. Below are some of the most common types.

  • Centre-pivot: This is popular for use in pitched roofs, in particular, those with loft extensions. Pitched roofs between 15° to 90° can accommodate centre pivot roof windows which are easy to open thanks to the position of the handle at the bottom. The VELUX GGU 0034 is a centre-pivot window perfect for use in rooms with high humidity such as bathrooms.
  • uPVC: These windows are also ideal for pitched roofs. Rooms that accrue a lot of condensation like bathrooms and kitchens benefit from their installation. The frames on uPVC windows are also extremely durable, requiring little to no maintenance.
  • Top-hung: This approach can provide an emergency exit which makes them perfect for restricted living spaces. The windows either pivot at the top or the ¾ point of the frame. They also include a trickle vent to allow air circulation even in situations where the window is closed. The VELUX White Painted GPL 2066 opens outwards and upwards to provide clear views outside.
  • Ventilated: These are similar to standard centre-point windows but also feature a trickle vent, similar to top hung windows. They are also great for pitched roofs between 15° to 90°.


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