Short answer: a leaking roof lantern is usually caused by the upstand (the kerb it sits on) not being waterproofed or sealed properly, ageing seals or gaskets on the glazing bars, a loose ridge or hip cap, or blocked drainage around the base. Misted glass means a sealed unit has failed, and cracked glass needs the unit replacing. A specialist can often replace seals or individual glazed units; full replacement is usually suggested when the frame is failing or problems are widespread.
How a roof lantern is put together
A roof lantern is a glazed, pitched structure — usually aluminium or uPVC-clad framing holding double or triple-glazed sealed units — that sits on a raised kerb called an upstand. The upstand, typically timber, is built into the flat roof and covered with the same waterproof membrane, which should run up its sides and seal against the lantern frame. Water runs down the glass, over the frame and onto the flat roof, where it needs to drain away rather than pool against the base.
Common roof lantern problems
| Problem | What you'll notice | Typical fix |
|---|---|---|
| Upstand or kerb leak | Water around the base of the lantern or staining on the ceiling just below it, worse in heavy rain | Re-dress or extend the membrane up the upstand and reseal the junction; rebuild a low or rotten upstand |
| Failed seals or gaskets | Drips from glazing bars, often at joints or the bottom of the bars | Replace gaskets and reseal caps |
| Ridge or hip cap issues | Leaks at the top of the lantern in wind-driven rain | Refix and reseal the ridge or hip caps |
| Misted sealed unit | Moisture trapped between the panes that can't be wiped away | Replace the individual glazed unit, where the system allows |
| Cracked glass | A visible crack, sometimes with a leak | Replace the unit promptly |
| Blocked drainage | Water pooling against the upstand after rain | Clear outlets and gutters; correct falls if water still sits |
| Condensation | Droplets on the inside of the glass on cold mornings | Improve ventilation, check seals and insulation around the upstand |
Why is my roof lantern leaking?
The upstand
The upstand is one of the most common sources of lantern leaks. If it's too low, water on the flat roof can sit against or over the junction. If the membrane stops short or isn't sealed to the lantern frame, rain finds its way in at the base. Timber upstands that have been wet for a long time can rot, which means rebuilding rather than resealing. Upstand problems are closely tied to the flat roof around it, so they're often fixed alongside wider orangery roof repair work.
Seals, gaskets and glazing bars
Like the glazing bars on a conservatory, lantern bars rely on rubber gaskets and caps to keep water out. As these harden or shrink, water gets under the caps and runs down inside the bar. Our page on conservatory roof seals and glazing bars explains how these parts work; the same principles apply to most lanterns.
The glass
A sealed unit that has mist or droplets between the panes has lost its seal. It won't usually leak water into the room, but it looks poor and insulates less well. Cracked glass is more urgent, as it can let water in and may be a safety issue overhead. Lantern units are often specialist sizes and shapes, so replacement units may need to be made to order.
Repair or replace the roof lantern?
A single leaking joint, one or two misted units, or an upstand that needs re-dressing is normally a repair job. Roof lantern replacement is more likely to be the sensible option when:
- The lantern leaks at several joints or keeps leaking after repairs
- Several units have misted, or replacement units for your system are hard to get
- The frame is distorted, corroded or poorly made
- You want better glazing — for example solar-control or self-cleaning glass, or a lantern with opening vents
- The upstand and surrounding flat roof are being rebuilt anyway
A replacement lantern usually means removing the old one, checking or rebuilding the upstand, fitting the new lantern and making good the membrane around it. If the opening size changes or structural work is needed, ask the provider whether Building Regulations approval is required. When choosing a new lantern, it's worth asking about glass coatings in the same way as for a glass conservatory roof.
Safety first: don't climb onto the flat roof to inspect or clean the lantern. Lantern glass and flat-roof decks are not designed for walking on. Look from inside and from the ground, and leave roof access to professionals with proper equipment.
What affects the cost of a lantern repair or replacement?
We don't publish prices because every lantern is different. The main factors are:
- Whether the job is resealing, a replacement unit, upstand work or a new lantern
- Lantern size, shape and frame system
- Glass specification and whether units must be made to order
- Condition of the upstand and the surrounding flat roof
- Access to the roof and any scaffolding needed
- Internal making good around the lantern opening
Roof lantern repairs in Liverpool
Lanterns are found on orangeries, flat-roof kitchen extensions and converted conservatories across the area, and we take calls from Woolton, West Derby and Maghull among other places. If your lantern is leaking or misted, call 07777 659786 and we'll aim to connect you with an independent local company who can inspect it and explain the options. We also cover conservatory roof repairs across Merseyside, so if the problem turns out to be elsewhere on the roof, the same call covers it. For the bigger picture, see our orangeries in Liverpool hub, or if you're thinking of adding a lantern to an existing conservatory, read about conservatory to orangery conversion. You can also find out more about our conservatory roof repair service in Liverpool.
Frequently asked questions
Why is my roof lantern leaking?
Common causes are a poorly waterproofed or too-low upstand, failed seals or gaskets on the glazing bars, loose ridge or hip caps, and blocked drainage causing water to sit against the base. A professional will trace the entry point before repairing.
Can a misted roof lantern unit be replaced on its own?
Often, yes. In many lantern systems an individual sealed unit can be replaced without replacing the whole lantern, though some units are special shapes that must be made to order. A provider can confirm what's possible for your system.
Is condensation on my roof lantern a leak?
Not necessarily. Droplets on the inside of the glass on cold mornings are usually condensation, caused by warm, moist air meeting cold glass. It tends to be worse with poor ventilation. Water appearing during rain, especially at the base or a joint, is more likely to be a leak.
Should I repair or replace my roof lantern?
One leak, a failed seal or a couple of misted units can usually be repaired. If the lantern leaks in several places, the frame is distorted, parts are unavailable, or the upstand and roof are being rebuilt anyway, replacement is often better value in the long run.
Can I clean my roof lantern myself?
You can clean the inside from a safe, stable position, but don't climb onto the flat roof to clean the outside. Lantern glass and flat-roof decks aren't designed to take a person's weight, so use a professional with suitable access equipment.