Things to look for when looking at VELUX replacement jobs

Replacing Your Old VELUX Roof Windows? Here’s What to Watch Out For

VELUX roof windows are built to last – many stay in place for 25–30 years. But when the time finally comes to replace them, it’s rarely as simple as swapping the old for the new. Over the decades, installation methods, roof coverings and even VELUX’s own designs have changed.

That means a straightforward replacement can quickly become tricky if your installer doesn’t know what to look for. Below are the most common issues with old VELUX windows – and why choosing the right installer makes all the difference.

Your Old Window Might Have Been Fitted Too High
Earlier VELUX models (with size codes like GGL–1 to GGL–9, or 101 to 810) were sometimes installed incorrectly. The brackets were fixed too low, causing the window to sit 25–40mm higher than it should.

• The result? A window that looks perched above the roofline, with exposed frame showing if side covers are removed.
• A good installer will spot this before quoting and allow for extra work, so the replacement sits properly with the right flashing kit.

Flashings May No Longer Be Available
If your roof covering has changed from slate to tile (or vice versa) and you want to keep the old window, you could be out of luck.

• Flashings for pre-2001 models (with all-numerical size codes) are no longer made.
• Modern flashings simply don’t fit older frames.
• In this case, the safest option is to fit a new window alongside your new roof covering.

Tiles Cut Too Close to the Frame                                                                                                    Many older installs have tiles or slates pushed hard against the sides or top of the window.

• When replacing, these need trimming back to leave the correct expansion and drainage gaps.                  • Done properly, this ensures your new window stays watertight.

Matching Roof Materials Around the New Window
Replacing a window often means disturbing surrounding slates or tiles.

• A skilled installer will carefully reuse or relocate tiles from less visible areas of the roof so the new section blends in seamlessly.

Flashing Apron Adjustments
Modern VELUX windows sit slightly lower in the roof than older ones.

• This means the opening often needs extending at the bottom to accommodate the new flashing apron.
• In many cases, it’s better to keep the old installation height, so the new window sits neatly without compromising rafter space.

Old Brackets Should Never Be Reused
Brackets from older windows can be slightly off, leading to misaligned sashes or sticking frames.

• Professional installers always use the new, supplied brackets and, on larger windows, fit the extra support brackets to prevent long-term distortion.

New Systems Solve Old Leak Risks
Older VELUX covers were fixed with screws, which could create water-ingress problems.

• Today’s push-fit systems are much more secure and watertight.

Plasterboard Grooves May Not Line Up
Smaller, older VELUX models (like GGL 102, 104, 206) were built with slimmer frames to maximise glass area.

• Their grooves don’t align perfectly with new windows, leaving small gaps.
• A quality installer will finish this neatly with trim or caulk so the lining looks professional.

Why This Matters for Homeowners

• Replacing a roof window isn’t just about swapping old for new. A careful installer will:

• Spot hidden issues before quoting.

• Use the correct flashing and brackets.

• Ensure surrounding tiles and plasterwork are finished neatly.

• Leave you with a watertight, long-lasting window that looks like it was always part of the roof.

Bottom line: When choosing someone to replace your VELUX windows, ask them about these common pitfalls. The right installer will know exactly what to look for – and how to put it right.

8 Things to Check Before Replacing Your VELUX

Thinking of replacing your old VELUX roof window? Here are 8 common issues to watch out for – and why choosing the right installer matters:

• Bracket height – Old windows (pre-2001) were often fitted too high. A new window may need re-sitting at the correct height.

• Flashing availability – Flashings for pre-V21 windows (all-numerical codes) are no longer made. In many cases, a new window is the only safe option.

• Tiles too tight – Old installs often have tiles/slates cut right up against the frame. These need trimming back for drainage and movement.

• Matching materials – Replacements can disturb surrounding tiles/slates. A good installer will carefully blend new and old for a neat finish.

• Flashing apron fit – Newer VELUX windows sit lower in the roof, meaning the opening may need adjusting.

• Brackets – Never reuse the old ones. Modern brackets (supplied with the window) prevent misalignment and frame distortion.

• Waterproofing – Old screw-fixed covers risked leaks. Today’s push-fit system is safer and more watertight.

• Interior finish – Older small windows had slimmer frames, so plasterboard

Tip: Always use an installer who knows these pitfalls. The difference between a quick swap and a professional replacement is 25 years of peace of mind