Three ways to deal with a tired glass roof
People searching for new glass roof panels usually have one of two problems. Either a few units have misted between the panes, or the whole room is uncomfortable. The fix depends on which.
| Option | What happens | Good for | Leaves you with |
|---|---|---|---|
| 1. New sealed units, like for like | Failed units swapped for new ones | A roof that is comfortable and only a few units have misted | The same heat and glare as before |
| 2. Whole roof in insulated panels | All glass out, panels in, frame kept | A room that is too cold in winter or too hot in summer | A warm, quiet room with a white ceiling |
| 3. Panels plus roof lights | As option 2, with glazed roof lights where you want sky | Keeping some daylight from above | Warmth with pockets of light |
We do options 2 and 3. If only one or two units are misted and you are happy in the room the rest of the time, a glazier replacing those units is the cheaper answer, and we will say so.
How to read your glass roof
Misting between the panes
If you see fog, droplets or a milky film that you cannot wipe off from either side, the seal round that unit has failed. Moist air has got into the gap. It will not clear on its own.
How old it is
Before about 2002, most roof glass was plain double glazing without a low-e coating. Those roofs have a U-value of around 2.8, which is worse than 16 mm polycarbonate. Modern low-e roof glass manages 1.0 to 1.2. A look at the date on the spacer bar inside each unit, or the paperwork from when the conservatory was built, tells you which you have.
What the room feels like
If the room is fine all year and only the look is the problem, new units are enough. If you avoid the room for half the year, the glass itself is the problem, however new it is.
The numbers for a typical glass roof
Take a Victorian of roughly 4 m by 3.6 m with about 16 m² of glass roof. The table shows the heat that leaves through the roof on a cold evening with 20 degrees between the room and the garden, and the yearly heat lost across an English heating season of about 2,150 degree days.
| Roof on 16 m² | U-value | Heat out at a 20 degree gap | Heat lost a year |
|---|---|---|---|
| Glass, before 2002 | 2.8 | about 896 W | about 2,310 kWh |
| Low-e glass, since 2002 | 1.2 | about 384 W | about 990 kWh |
| Our insulated panels | 0.43 | about 138 W | about 355 kWh |
From old glass to panels, that is about 1,960 kWh a year, or roughly £515 if electric heaters warm the room at 26.32p a unit (the Ofgem cap), and about £173 with gas at 7.97p through a 90% boiler. From modern low-e glass, the winter saving is smaller: about 636 kWh, or around £167 on electric.
Honestly, if your glass is modern, summer is where you feel the change most. Low-e glass still lets strong sun straight into the room. A panel roof puts 75 mm of foam between the sun and your chair.
Weight: why taking glass off helps the frame
Roof glass weighs a lot. One sealed unit with a pair of 4 mm panes comes to roughly 20 kg per square metre, before the frame and beads. A 16 m² glass roof puts around 320 kg of glass alone onto your conservatory frame. An insulated panel of aluminium and foam weighs a fraction of that for the same area.
So swapping glass for panels takes load off the frame, not on. We still check the bars, wall plate and base at survey, but a frame that has carried glass for twenty years is rarely troubled by something lighter. Our guide on how heavy roof panels are goes into the detail.
How a glass roof comes off
Glass takes longer to remove than polycarbonate, and it needs care. On the day:
- We protect the floor and furniture and set up safe access outside.
- Bar caps and beads come off, one bay at a time.
- Each unit is lifted out by two people using suction handles and taken straight down to the van.
- With the glass out, we inspect the bars and seals and clean the rebates.
- Panels go in bay by bay, sealed and capped as we go.
- Flashing, trims and gutter checks finish the job.
The old units leave with us for recycling. Most glass roofs are done within the usual timings: about 1 day for small, 1 to 2 days for medium and 2 to 3 days when the roof is large, with no scaffold on most single storey conservatories.
What it costs
Swapping glass for panels is priced exactly like a polycarbonate swap of the same shape and size. That covers the fitting, taking every glass unit away, your chosen colour outside, the building control paperwork and ten years of insurance backed cover.
- Up to 12 m² of roof: from £3,000.
- Between 12 and 25 m²: from £4,000.
- Over 25 m²: from £5,000.
For comparison, published UK cost guides put a like for like new glass roof on a 3 m by 3 m conservatory at roughly £3,300 to £5,200. The price page has every style and size.
Keeping some sky
If you love looking up through a glass roof, option 3 keeps a little of that. Glazed roof lights at £395 each go into the panel roof wherever you want a patch of sky, usually close to the house wall. They are made for the panel roof, rather than reusing old units. Pair them with LED spotlights for £345 for the evenings. Details on the roof lights page.
Approval and planning
A glass roof counts as translucent, which is part of what keeps a conservatory exempt from building regulations. Panels are opaque, so the room loses that exemption and building control will need to approve it. We discuss the spec with them before your panels are ordered and send in the application for you. Planning is a rarer concern: the conservatory is no bigger or taller afterwards. Ask us first if your house is listed, sits inside a national park or a conservation area, lies in a National Landscape, or has had permitted development rights withdrawn. Compare the other roof types on the insulated conservatory roof page.
Questions
How do I know if a glass roof unit has failed?
Look for fog, droplets or a milky film between the two panes that will not wipe away from either side. That means the seal has gone and damp air has got in.
Is taking a glass roof off more work than polycarbonate?
Yes. Each sealed unit is heavy and has to be lifted out carefully by two people, so removal takes longer. It stays within our usual 1 to 3 day fitting times for most roofs.
Can I keep one or two of my glass units as windows in the new roof?
We fit new glazed roof lights at £395 each instead, because they are made to sit properly in the panel roof and seal against it. Old units were never designed for that.
Is a modern low-e glass roof worth replacing?
In winter the gain is smaller than from old glass, about 636 kWh a year on a 16 m² roof. The bigger change is in summer, when a panel roof stops the sun pouring straight through.
Does taking off a glass roof make the frame work less hard?
Yes. A roof unit with a pair of 4 mm panes is roughly 20 kg per square metre, and aluminium and foam panels weigh far less, so the frame carries less load afterwards.
