VELUX Roof Window Replacement Guide

Thinking About Replacing an Old VELUX Roof Window?

Older VELUX roof windows can last for many years, but over time glazing, seals and finishes naturally wear. Replacing an older unit with a modern VELUX window can dramatically improve comfort, energy efficiency and appearance.

This guide explains how to identify your existing window, match the right replacement and decide when it’s time to upgrade.

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1. How to Identify Your Existing VELUX Window

Every VELUX roof window has an identification plate with a size and model code.

• Open the window and look at the top edge of the sash.
• You should see a small plate showing the type and size code (for example, GGL MK04).
• Older windows may have slightly different coding, but the plate still helps match a replacement.

The size code (such as MK04, CK02, PK06) is crucial for choosing the correct replacement model and flashing.

For a full explanation of size codes, see our VELUX Roof Window Size & Code Guide.

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2. When Should You Replace a VELUX Window?

Common signs that it may be time to replace your window include:

• Condensation or misting between glazing panes.
• Drafts around the frame or noticeable heat loss.
• Leaks or water staining around the window.
• Stiff, worn or damaged hinges and handles.
• Discoloured, swollen or cracked timber on older pine frames.

If your VELUX window is more than 15–20 years old, upgrading to a new model can provide better insulation, improved operation and a fresher appearance.

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3. Matching Old VELUX Codes to New Models

In many cases, you can replace an older VELUX window with a new white-painted model using the same size code. For example:

• An older GGL MK04 can usually be replaced with a new white-painted centre pivot GGL MK04.
• Where the size code matches, the existing structural opening is often suitable.

Even if the model name has changed over the years, matching the size code is usually enough to choose a direct replacement.

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4. Upgrading Glazing and Finish at the Same Time

Replacing a window is a great opportunity to upgrade performance and appearance:

• Glazing: Move from older double glazing to modern, energy-efficient glazing such as 2070, or even triple glazing.
• Finish: Upgrade from aged pine to modern white-painted timber for a brighter, cleaner look.
• Ventilation: Newer models often feature improved ventilation options and better seals.

For help choosing glazing, see our VELUX Glazing Options Guide.

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5. Do I Need New Flashings for a Replacement?

In most cases, it is recommended to install new flashings when replacing a roof window, especially if the existing flashings are old or weathered.

• New flashings ensure a weather-tight seal.
• They are designed to work with the latest window designs.
• They help reduce the risk of future leaks.

You’ll need flashings that match the new window size and your roof covering (for example EDW, EDL or EDP). For more detail, see our VELUX Flashing & Installation Guide.

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6. Replacement vs New Opening

There are two main scenarios:

Like-for-like replacement

• Replaces an old VELUX with a new one of the same size.
• Usually quicker and less disruptive.
• Generally cheaper than creating a new opening.

New window or larger opening

• Requires changes to rafters and roofing materials.
• Higher installation cost and more time.
• Ideal if you want significantly more daylight.

For typical cost ranges, see our VELUX Installation Costs & Considerations Guide.

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7. Replacing Blinds and Accessories

If you’re upgrading your window, it’s also a good time to update blinds and accessories:

• New blackout blinds for bedrooms.
• Translucent blinds or pleated blinds for living areas.
• External awnings or shutters to help reduce overheating.
• Installation accessories such as insulation collars to improve performance.

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8. DIY Replacement vs Professional Installation

Some experienced DIYers replace VELUX windows themselves, but many homeowners prefer to use a professional installer.

• Professional roofers ensure correct integration with tiles, slates and membranes.
• They can quickly identify and resolve any issues with the existing opening.
• They help ensure a weather-tight, long-lasting finish.

If you are unsure what your project will involve, it’s sensible to get advice and a quotation before ordering.

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9. Summary: Steps to Replacing Your VELUX Roof Window

• Find the identification plate and note the size code.
• Decide if you want a like-for-like replacement or a size upgrade.
• Choose your finish (white painted or pine) and glazing option.
• Select the correct flashing kit for your roof type.
• Plan installation with a trusted roofer or installer.
• Consider adding blinds and accessories at the same time.

If you need help at any stage, our team is here to support you with practical, project-specific advice.

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