How to Fit a Velux Window

Velux Roof Windows are some of the finest in the industry. Renowned for their astounding build quality, visual appeal, and innovative features. They are popular among professional builders and DIY-savvy homeowners alike, as their intuitive design makes installing a Velux window much more straightforward than much of the competition.

Fitting a roof window yourself can be tricky, but if you plan and prepare sensibly, it’s well within reach for an experienced DIYer. We’re going to talk you through the main steps below, from seeking planning permission should you need it, right up to complete installation.

How to Install a Velux Window

Before You Begin

It’s important to take all necessary precautions and plan your project out thoroughly before you begin. After all, your roof is one of the most vital parts of your home’s structure, so careful planning is a must. First, ensure that your project doesn’t require planning permission. This isn’t usually an issue, as most fitting a Velux window would usually fall under Permitted Development, but it’s important to check.

According to, there are three main limits and conditions on roof window installation to consider:

  • Any alteration to project no more than 150 millimetres from the existing roof plane.
  • No alteration to be higher than the highest part of the roof.
  • Side facing windows to be obscure-glazed; any opening to be 1.7m above the floor.

You should also make sure that any roof window project you undertake will meet or exceed all Building Regulations, click here for a basic overview of these. Once you’ve completed your Velux window project, you should obtain a certificate from your local authority to confirm that it’s up to energy efficiency standards. Find your Local Authority Building Control Team.

Getting Started

Now that you’re sure your roof is suitable for a Velux window, and you’ve obtained any planning permission you need, it’s time to begin.


Here’s the kit you’ll need to successfully fit a Velux window:

  • Pencil
  • Tape Measure
  • Ladder
  • Hammer
  • Screwdriver
  • Utility Knife
  • Spirit Level
  • Crowbar
  • Tin Snips
  • Panel Saw
  • Staple
  • Angle Grinder
  • Safety Goggles
  1. Using a pencil or some other kind of marking tool, mark the rafters at the corners and the centre of where your new Velux window will be.

  2. It’s now time to remove any felt or battens from your roof. Begin at the centre and work your way outwards towards the sides and corners where your new roof window will be placed. This will expose your roofing materials, which also need to be removed. The exact process for removing these will depend on what type of roof you have. For tiles, the most common material on pitched roofs in Britain, simply lift them off and pull them back between the rafters. The exposed space for your new window should measure between 40 and 60cm larger than the window’s size.

  3. You should then move onto making sure your window opening is square. Fasten the top and bottom support battens using a spirit level to ensure they are true and flush.

  4. You can then set up the Velux insulation collar, one of Velux’s many fantastic window accessories. This is done by clipping the corners together, and then moving through the opening. This is where it should be placed ready for the window to be installed.

  5. Now it’s time to turn your attention the window itself. You can detach the window frame from its sash by unlocking the hinge, which should be easy to find and operate. You can then screw the brackets onto the frame of the window before placing it into the opening you have created. Here, you can screw into the bracket holes and through the batten, as well as into the rafter to fully secure the bottom part of the frame.

  6. You can now reattach the sash, which can be done by lining the hinged pieces up with the matching slots on the frame. Once this has been done, check for any uneven spacing. This is crucial, as it plays a big part in your window’s durability. Any uneven spaces should be crowbarred into place. Once all spaces are even, screw in the top brackets to secure the window properly.

What do I do Next?

While your window is fitted, it is not yet fully installed, and are a couple more things you need to do to ensure that it functions as it should.

  1. First, you should fit your underfelt collar by installing it at an angle, which will allow water to run off it properly. It should be fitted tightly to the edges of the window frame and can then be stapled to the battens.

  2. Gutters can then be placed at the top of the window, and the underfelt collar over and into it, fixing in place with the clips that are provided.

  3. You can then re-install the roof tiles underneath your windows before adding your flashing. It should be noted that Velux makes a range of window flashings, each designed to work with different roofing materials, so it is vital to make sure you purchase the right type. Ensure that the bottom apron of your Velux window flashing is dressed smoothly against the tiles.

  4. Roof tiles or slates may need to be cut to ensure a smart, weathertight finish around your Velux window. You can use an angle grinder for this.

  5. Once the sash has been re-attached to the window frame, you can attach your vapour barrier to the roof’s existing breather membrane to help combat moisture ingress.

And you’re done!

You’ve now installed a beautiful, brand-new Velux window that will stand the test of time. We stock a massive range of gorgeous Velux blinds, including those designed to work with their electric and solar-powered opening. So, if you’d like to add that perfect finishing touch to your new window, we’ve got just what you need.

If you’re still unsure about the process, or which Velux window is right for you, get in touch with our award-winning customer service team. With over four decades’ experience in all things DIY and roofing, they’re sure to help get your project going as soon as possible. Call them on 01295 565 565, email [email protected] or use the handy live chat on our website.

Please note: This guide on 'How to Fit a Velux Window' has been written for information purposes and we therefore take no responsibility for any purchasing decisions you make or installation processes you follow as a result of reading this article. Whilst we act as a retailer, we are not experts nor qualified in the installation of roof windows or roofing materials. We therefore recommend that you refer to your manufacturer's guide and, if appropriate, consult a qualified professional.