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How do you install a Velux window?

Updated: Aug 14, 2023

Velux window

Velux windows are renowned for their exceptional quality and functionality, making them a popular choice for homeowners looking to enhance natural light and ventilation in their homes. Installing a Velux window requires careful planning, preparation, and execution to ensure a successful and watertight installation. In this comprehensive guide, we will walk you through the step-by-step process of installing a Velux window in the UK, providing you with the necessary information to undertake this project with confidence.


Before embarking on any DIY project, it is crucial to consult the manufacturer's instructions and guidelines specific to the Velux window model you have purchased. Additionally, if you are uncertain about any aspect of the installation, it is advisable to seek professional assistance.

Materials and Tools:

To install a Velux window, you will need the following materials and tools:


1. Velux window (with flashing kit, insulation collar, and installation screws)

2. Roofing felt

3. Roofing nails

4. Roofing adhesive

5. Underfelt collar

6. Insulation material

7. Plasterboard (if required)

8. Plasterboard screws (if required)

9. Timber battens (if required)

10. Exterior-grade sealant

11. Interior finish materials (e.g., plaster, paint, or trim)


1. Tape measure

2. Spirit level

3. Hammer

4. Roofing knife

5. Chalk line

6. Screwdriver

7. Drill

8. Pliers

9. Crowbar

10. Saw (if required)

11. Safety equipment (gloves, safety glasses, etc.)

Step 1: Planning and Preparation

1. Ascertain the desired location for your Velux window, considering factors such as sunlight, views, and room functionality.

2. Measure the window opening to ensure compatibility with the Velux window size you intend to install.

3. Check with your local authorities regarding any planning permissions or building regulations that may apply

to your installation.

4. Purchase the Velux window and any additional accessories required for installation, based on your measurements and specifications.

Step 2: Gather Information and Familiarize Yourself with the Manufacturer's Instructions

1. Carefully read the manufacturer's instructions provided with your Velux window. Pay special attention to any specific guidelines, recommended installation techniques, and safety precautions.

Step 3: Preparing the Opening

1. Safely access the roof using ladders or scaffolding, ensuring all necessary safety precautions are taken.

2. Remove any existing roofing materials around the window opening, ensuring a clear and clean area for installation.

3. Mark the dimensions of the window opening on the roof using a chalk line, following the guidelines provided by the manufacturer.

4. Cut through the roof surface along the marked lines using a roofing knife or saw, being cautious not to damage any underlying structures.

Step 4: Install the Flashing Kit

1. Position the appropriate flashing kit provided by Velux around the window opening.

2. Carefully follow the manufacturer's instructions to secure the flashing kit in place using the provided screws and roofing adhesive.

3. Ensure a secure and weatherproof seal between the flashing and the roof surface, paying attention to the specific instructions for your flashing kit.

Step 5: Install the Insulation Collar (Continued)

1. Attach the insulation collar to the underside of the Velux window frame, aligning it with the opening and ensuring a snug fit.

2. Secure the insulation collar to the window frame using the screws provided by Velux, following the manufacturer's instructions.

Step 6: Prepare the Roofing Surface and Underfelt Collar

1. Cut the roofing felt to size, allowing for an overlap of at least 150mm around the window opening.

2. Lay the roofing felt over the window opening, ensuring it is smooth and taut.

3. Secure the roofing felt in place using roofing nails, ensuring it is securely fastened to the roof surface.

4. Install the underfelt collar provided by Velux, placing it over the roofing felt and aligning it with the window opening.

Step 7: Install the Velux Window

1. Carefully lift the Velux window into position, aligning it with the opening and the flashing kit.

2. Ensure the window is level and plumb using a spirit level. Adjust as necessary.

3. Secure the window in place using the screws provided by Velux, following the manufacturer's instructions.

4. Double-check the window's level and alignment before fully tightening the screws.

Step 8: Insulate and Finish the Interior

1. Apply insulation material around the window frame, filling any gaps or voids to ensure optimal energy efficiency.

2. If required, install timber battens around the window opening to provide additional support for plasterboard or other interior finishes.

3. Install plasterboard or other interior finishes as per your preference and local building regulations.

4. Secure the plasterboard using plasterboard screws, ensuring a secure and even installation.

5. Finish the interior by applying the desired wall treatment, such as plaster, paint, or trim, around the Velux window.

Step 9: Exterior Sealant and Finishing Touches

1. Apply an exterior-grade sealant around the perimeter of the Velux window, ensuring a watertight seal between the window frame and the roof surface.

2. Inspect the entire installation, checking for any gaps, leaks, or areas that require further sealing or finishing.

3. Clean the window and surrounding area, removing any debris or construction materials.


Installing a Velux window in the UK can significantly enhance the aesthetics and functionality of your home. By following the step-by-step guide provided above and adhering to the manufacturer's instructions, you can successfully install a Velux window, allowing natural light to flood your space while ensuring weatherproofing and energy efficiency. Remember to prioritize safety, consult local regulations, and consider seeking professional assistance if you are uncertain about any aspect of the installation. Enjoy the benefits of your new Velux window and the transformed atmosphere it brings to your living space.

We fit velux windows

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