Why one number does not fit every rooflight
Ask how long a rooflight lasts and the honest reply is another question: which part? The glass, the frame, the weathering and any moving parts each have their own working life, and the shortest of them sets when the whole skylight is due for replacement.
Think of a pitched roof window in a Romsey loft. It has a double or triple glazed sealed unit, a timber or polyurethane coated frame, a sash with hinges and a handle, and a flashing kit that ties it into the slates. A flat rooflight on a rear extension in Chesterton has a glass unit, an aluminium or uPVC frame and an upstand dressed into the roof membrane. A roof lantern adds glazing bars, a ridge and hips, and many more seals. More joints mean more places where age shows first.
So a lifespan figure is only useful once you know which component it describes. The table below gives a general guide by part, and the rest of this page covers what pushes an individual rooflight towards the short or the long end. If you are not sure what kind of skylight you have, our guide to types of rooflight will help you place it.
Typical service life, part by part
As a general guide, the sealed glass unit is the component that sets the clock, while well-made aluminium frames and properly fitted flashings can outlast it. These are broad market ranges, not a promise for any product.
| Part | General guide | What ends it |
|---|---|---|
| Sealed glass unit | Commonly 20 to 30 years | Edge seal fails, unit mists |
| Aluminium frame | Can outlast the glass | Finish wear, dated design |
| uPVC frame | Broadly similar to the glass | Discolouring, brittle trims |
| Timber roof window | Depends on finish upkeep | Damp in the frame |
| Plastic dome | Usually shorter than glass | Yellowing, crazing in sunlight |
| Motor or opener | Shorter than the unit | Wear on moving parts |
Two points sit behind those rows. First, the glass itself does not wear out; the seal around the edge of the unit does, and once moisture gets past it the cavity mists and the insulating gas escapes. Second, older plastic domed skylights and early polycarbonate rooflights age in a different way from glass: ultraviolet light slowly clouds and embrittles them, which dims the room long before anything lets water in. Our page on misted and failed rooflight replacement looks at the glass side of this in more depth.
What shortens a skylight's life
Early failures tend to trace back to water that sits where it should run off, heat that cycles hard every day, or a fit that was not quite right from the start. Each is predictable, which means each can be planned around.
- Too little fall on a flat roof. A flat rooflight needs an upstand and enough fall that rain clears the glass. Where water ponds against the frame, it works at the edge seal of the unit for years.
- Hard sun on a south or west slope. Cambridge is flat, so very little shades a roof. A south facing pane sees the full summer sun, and the daily swing between a cold dawn and a hot afternoon flexes the seals more than on a north slope. Our skylight orientation guide explains how each slope behaves across the year.
- A poor original fit. A frame that is out of square, flashing that is short at the head, or an upstand left uninsulated puts stress and condensation where the maker never intended.
- Condensation inside the room. A humid bathroom or kitchen with no extract keeps the inner frame and reveal damp, which is hard on timber and on the plaster around the lining.
- Leaves and moss. Debris building up at the top edge holds water against the frame through the winter.
What helps a rooflight reach the long end
The biggest influence is the decision made before the roof is ever cut: the right product for the slope, the right glass for the light, and a careful installation to current Building Regulations.
After that, the care is simple. Clear leaves from around the frame each autumn, wash the glass so grit does not build up at the edges, and on an opening roof window check that the hinges and ventilation flap move freely and the drainage channels are clear. Our rooflight cleaning and care guide sets out a sensible routine. Keeping moisture down in the room below, with an extractor in a bathroom and the ventilation flap open when cooking, protects the lining as much as the unit.
Manufacturer warranties on glass and frames vary by brand and range, so keep the paperwork and note the details on the product label. If you ever need to identify an older unit, our answer on how to tell what skylight you have shows where the codes are usually found.
When the end comes: replace, and plan the light again
A skylight at the end of its life is replaced, and that replacement is a chance to get better light than you had before, not just a newer version of the same opening.
The signs are usually clear: misting between the panes that no longer clears, a cloudy or yellowed dome, a sash that no longer closes tight, or damp staining around the lining. At that point the sensible options are a like for like swap, a larger unit, a change of type, or a move to a better position. Our guide to skylight replacement options compares them.
A rooflight fitted twenty years ago may well have been chosen for the roof rather than the room. Modern sealed units carry better low emissivity coatings and warm edge spacers, and solar control or laminated glass can deal with the heat and rain noise an older pane let through. If the old skylight lit the ceiling and left the table in shade, its replacement can be sized and placed to put the light where you actually use it. The written light plan that comes with every Vision Skylights quote records that position, the glass and the shading, and the reason for each. You can read more about how we approach planning the light, or start from our skylight and rooflight installation overview.
Questions people also ask
Do rooflights last as long as the roof around them?
Not usually. A slate or tile roof covering can last far longer than a sealed glass unit, so a rooflight will generally be replaced at least once during the life of the roof. On a flat roof, the covering and the rooflight can be closer in age, which is why replacing both together during a reroof can make sense.
Can a misted skylight be left as it is?
It will keep the weather out for a while, but the misting will not clear on its own, the insulating value has already dropped, and the view and light through it will only get worse. Planning a replacement is the better route.
Does triple glazing last longer than double glazing?
Not in any simple way. Both rely on the same kind of edge seal. Triple glazing improves heat loss and noise, and its lifespan still comes down to the quality of the unit, the slope it sits on and how well it was fitted.
How long does it take to replace an old rooflight?
A like for like swap of a single roof window is usually a short job, while a larger or upsized flat rooflight takes longer. Our answer on how long skylight replacement takes gives typical timescales.
