If your VELUX roof window has misted glass, a cracked pane or a draughty, noisy feel, you can often upgrade the sealed glass unit without replacing the whole window. That means a shorter visit, less disruption and no change to your roof opening. This guide explains when a glass-only upgrade is the right call, what to check before you book, and when a full window replacement is the better route.
What a VELUX glass upgrade actually involves
A roof window is made of a frame, a sash that opens, and a sealed double glazed unit set into the sash. The glass upgrade swaps that sealed unit for a new one, ideally with better insulation or sound performance, while the frame, flashing and roof covering stay where they are.
The sealed unit is two or more panes held apart by a spacer bar, with a gas or air gap between them. When the seal breaks, moist air gets in and you see condensation or a milky haze between the panes. The unit has failed and needs replacing.
Common reasons people upgrade the glass:
- Misting or fogging between the panes, which means the seal has failed.
- Cracked or chipped glass from hail, a falling branch or a knock during loft work.
- Cold spots and draughts from an older, lower-performing unit.
- Noise from rain, traffic or aircraft, which is far more noticeable through a sloping roof window.
If you are not sure whether your problem is the glass or something else, our guide on how to know if your Velux window needs replacing walks through the signs.
Glass only or the whole window?
This is the question most readers have, and the honest answer is that it depends on the age and condition of the window as a whole.
VELUX says a roof window typically lasts 20 to 30 years, after which seals often fail, leading to leaks, constant condensation and reduced energy efficiency. The same page lists persistent draughts, discoloured or broken glass and moisture around the frame as signs it is time to act.
| Your situation | Glass-only upgrade | Full window replacement |
|---|---|---|
| Frame sound, glass misted or cracked | Usually the sensible fix | Rarely needed |
| Timber rotting or leaks around the frame | Will not solve the leak | Better option |
| Window at the end of its 20 to 30 year life | Possible, but weigh up the frame | Often better long term |
| You want a bigger glazed area or electric opening | Not possible | Suits this goal |
| Noise or heat is the main complaint | Strong option with the right glass | Also an option |
The pattern is simple. If the frame, hinges and flashing are in good order, new glass gives you most of the benefit with the least upheaval. If the frame itself is failing, new glass in a failing frame is a short-term fix, and we will tell you so.
Check the details before you order anything
VELUX has changed its product dimensions and mounting systems over the decades, so assuming a standard size is how people end up with a unit that does not fit.
- Find the data plate. VELUX describes it as a label with the exact product information, and its guidance on finding the data plate explains where it sits on different products. On many windows it is behind the ventilation flap.
- Note the production code. The code tells you the size and the era of manufacture.
- Check the age. Windows made before 2001 often have a thinner sealed unit than later ones. Some modern units need an adaptor or conversion arrangement to fit an older sash, which is one reason a survey beats guesswork.
- Look at the condition of the sash and seals. Perished rubber seals or damaged flashing should be fixed during the same visit.
You can see how we approach these jobs on our VELUX window repair page.
Choosing the right glass specification
Upgrading is the moment to choose better glass, rather than simply copying what failed. These are the choices that matter.
Insulation and low-emissivity coatings
A low-emissivity coating reflects heat back into the room in winter and helps limit solar heat gain in summer. Combined with a sealed gap filled with a low-conductivity gas, it can transform a cold loft room. Our guide to window U-values explains the rating in plain English: the lower the figure, the less heat escapes.
Warm edge spacers
The spacer bar around the edge of the unit matters more than most people expect. The Rooflight Association’s specification guide for glass rooflights recommends warm edge spacers because they reduce thermal bridging compared with traditional aluminium spacers, a common cause of condensation at the very edge of the pane. Ask any installer, including us, what spacer is in the quoted unit.
Laminated and acoustic glass
Laminated glass has a plastic interlayer bonded between glass layers. It holds together if broken, which is a safety benefit overhead, and it dampens sound. VELUX notes that triple-layer glazing can reduce external noise for homes near busy roads or flight paths while also improving thermal insulation. If noise is your main problem, read about our soundproofing and noise reduction glass.
Insulated glass in general
Our insulated glass service covers sealed units built for energy efficiency.
Building Regulations: what to know in England
Replacing glass is not always treated the same as replacing a whole window, so check before work starts. In England, Building Regulations require replacement windows, including roof windows, to meet set thermal performance standards. For existing dwellings, a replacement roof window typically needs a maximum U-value of 1.4 W/m²K. You can show compliance by using an installer registered with a Competent Person Scheme such as FENSA or CERTASS, or by submitting a Building Notice to your local authority building control.
The Rooflight Association’s quick guide to the approved document notes that roof window limiting U-values depend on the circumstances of the installation, so the figure above is a starting point, not a universal answer. Your installer or building control team should confirm which one applies to your project.
Two further points:
- Scotland, Wales and Northern Ireland have their own building standards. The England figures above should not be assumed to apply there. If you are in Scotland, ask your installer or local authority which standard applies.
- Commercial and housing association premises often face stricter fire safety and escape route requirements. The same Hampshire guidance reminds owners that using a registered competent person or a professional glazing service helps ensure the Building Regulations certificate and other paperwork is filed correctly, avoiding legal or insurance problems later. See also our Building Regulations guide for windows.
Our view: why we replace the glass, not the frame
At Cloudy2Clear Windows we have repaired and replaced double glazing for homes and businesses since 2005, and one lesson has held every year: most people call us about a symptom, not a full-window problem. A misted pane or a cracked unit is a glass problem, and treating it as one means a shorter visit, less mess and a smaller job on your roof.
We replace only the glass, not the frame, which keeps disruption down and gets you back to a clear, efficient window faster. But we are straight with customers about the limits. If the frame is rotten or the window leaks around the edges, we say so, because glass in a failing frame will not give you a result you will be happy with in five years.
We also encourage people to treat a glass repair as a chance to improve. You are already having the unit replaced, so the better specification, whether that is improved insulation, acoustic laminated glass or warm edge spacers, is a small step from there. Our glass comes with a 25-year guarantee.
Planning the work around the rest of your roof
A glass upgrade is a good moment to look at the roof around the window. Flashing, tiles and sealant near the window affect whether new glass stays dry and efficient. If your roof is ageing generally, this overview of roof upgrade ideas for homeowners is a helpful way of thinking about which improvements are worth doing first. It focuses on Florida shingle roofs, so the materials differ from most UK roofs, but the idea of ranking repairs by payoff applies anywhere.
VELUX states that replacing a whole roof window can often be done in as little as four hours from inside the room, with no structural changes. A glass-only visit is typically less involved, and we confirm timing once we have seen your window.
Before the visit:
- Clear the area under the window and protect furniture and flooring.
- Make sure we can reach the window safely from inside.
- Have the data plate photo or production code ready.
- Tell us about any leaks, stains or draughts you have noticed.
Homes, landlords and commercial buildings
Our customers include homeowners, small businesses and housing associations, and the same principles apply to each, with a few extra considerations.
- Homeowners: focus on comfort, noise and condensation. Choose a specification for the room’s use, such as a bedroom that needs quiet or a loft office that overheats.
- Landlords and housing associations: keep records. Record the window’s code, the specification fitted and any certificate issued, so later inspections are simple. Our inspection and full replacement service is built for this kind of portfolio work.
- Businesses: roof windows over offices, stairwells and shared spaces can have safety and escape implications. Our commercial window repair team can advise. Our article on window safety for businesses includes a compliance checklist.
Book a VELUX glass upgrade with Cloudy2Clear Windows
We replace failed, misted and cracked glass units in VELUX and other roof windows, along with conservatory, commercial, door and caravan glass, and we cover the UK through local branches. Our lines are open Monday to Friday, 8:30am to 6:30pm. Start with our VELUX window repair service, or browse all our services to see what else we can do on the same visit.
Frequently asked questions
Can you replace just the glass in a VELUX window?
Yes, in most cases where the frame and sash are sound. The sealed unit is swapped for a new one that matches your window’s production code, and the frame stays in place. If the frame is damaged, a full replacement may be the better option.
How long does a VELUX roof window last?
VELUX gives a typical lifespan of 20 to 30 years. After that, seals often fail, which leads to leaks, condensation and poorer energy efficiency. Well-maintained windows can do better, while neglected ones may need attention sooner.
Is it better to replace the whole window or just the glass?
If the frame is in good order, glass alone usually gives you the improvement you want with less disruption. If the window is near the end of its life, or you want a larger glazed area or electric operation, a full replacement can offer better long-term value. We will give you an honest view once we have inspected it.
Do I need Building Regulations approval for new roof window glass?
In England, replacement windows including roof windows must meet thermal standards, and compliance is shown through a competent person scheme installer or a Building Notice. Rules differ in Scotland, Wales and Northern Ireland, so ask your installer which applies to your property.
