The short answer
A well-made glass rooflight can stay in place for decades, but the parts inside it do not wear at the same rate. The sealed glass unit and its edge seal tend to fade first, then gaskets and sealants, then the frame. A plastic dome ages faster than glass. Age alone is a poor guide, so look at what the unit is doing.
What wears out first on a rooflight
A rooflight is a stack of parts, and each one has its own clock. The frame rarely decides the end of the story. The sealed unit does.
A double or triple glazed unit is two or three panes held apart by a spacer, with a seal running round the edge. That seal keeps moisture out of the cavity and keeps the gas fill in. A roof takes more punishment than a wall: sun from above, frost that settles on the glass overnight, rain that runs straight down the pane, and a wide swing between a cold night and a bright afternoon. Every one of those cycles moves the glass and the edge seal a fraction. Over a long enough time the seal gives way, and the cavity lets in damp air.
Gaskets and sealants round the frame age separately. Rubber and silicone dry, harden and shrink. A gasket that has lost its spring stops pressing the glass firmly into the frame, which matters for water and for sound alike. Aluminium and timber frames outlast all of this, so the usual pattern is a sound frame holding a tired unit.
| Part | What ages it | What you notice |
|---|---|---|
| Sealed unit edge | Sun, frost, movement | Mist between panes |
| Gaskets and sealant | Sun and drying out | Rattle, draught, stains |
| Flashing and upstand finish | Weather and movement | Marks on the ceiling |
| Opening gear | Use and dirt | Stiff or uneven opening |
Our page on signs a rooflight has failed goes through each of these in more detail.
Glass, plastic and the different lifespans
Material sets the ceiling on age. A glass rooflight and a plastic dome sit in very different places on the curve.
Glass does not degrade in sunshine. Its coatings are sealed inside the cavity where weather cannot reach them, so a glass unit keeps its clarity until the edge seal fails. That is the main reason a good glazed rooflight is treated as a long-term part of the house. Toughened outer panes shrug off weather and cleaning. A laminated inner pane adds safety overhead, because laminated glass stays together if it is struck.
Acrylic and polycarbonate domes are different. Plastic yellows and crazes under ultraviolet light, it scratches when cleaned, and it flexes in wind. A single-skin dome also has almost no insulation and very little to stop rain noise. The plastic can look worn long before water gets through, which is why an owner of an old dome can find the room colder and duller than they remember. Our answer on replacing a plastic dome skylight with glass explains what changes when the roof gets a glazed unit.
Timber, aluminium and PVC frames each age differently too. Bare timber needs its coating kept up, aluminium is left alone, and PVC can fade and warp in strong sun. Roof windows with opening sashes also carry hinges and gear that wear with use, so an opening unit has more moving parts to renew than a fixed one.
Why the same unit lasts longer on one roof than another
Two rooflights of the same age can be in very different shape. The difference is usually where and how they were fitted.
- Exposure. A south-facing unit takes more sun and more heat cycling than a north-facing one, so its seals age sooner. Shade from trees changes the pattern again.
- The upstand and flashing. A kerb that is well insulated and properly dressed keeps the frame dry and steady. A thin or poorly finished kerb lets the joint between glass, frame and roof move and weep.
- Quality of the original glazing. A cheap sealed unit with a poor edge seal gives up early. A unit made with a good spacer and sealant lasts much longer in identical conditions.
- Pitch. A rooflight laid at a very shallow fall holds water on the glass for longer, which is hard on the edge seal. A steeper pitch sheds it.
- Cleaning habits. Hard scraping scratches plastic and strips coatings. Soft cleaning leaves everything intact.
This is also why a new unit fitted with a new upstand tends to age better than one dropped into a tired kerb. The kerb and flashing are part of the product, not an afterthought. The detail is in our service page on flat roof rooflight installation.
Telling that yours is near the end
A rooflight usually gives notice. The signs are small, and they are easy to put off noticing for a year or two.
Mist or droplets trapped between the panes that never clear is the classic sign. The unit may still keep the rain out, but it no longer insulates as it should and the daylight through it turns dull. A faint brown or green tide line or a film on the inner faces of the glass points the same way.
Loose or hardened gaskets show up as whistling, rattling in a gale or cold air at the frame. In the room, they also show up as a louder downpour, because a unit that is not gripped firmly passes more sound. A stained or bubbled ceiling beside the opening, or a damp patch on the reveal, means water is finding a path round the unit and the flashing needs to be renewed with it.
On the roof, look for a dome that has gone cloudy or cracked, a frame that has warped, or a sash that no longer closes flat. If you find one of these, the useful question is not whether the unit has reached a certain age. It is whether replacing the whole unit now costs less than living with it, and our page on when to replace a rooflight helps you weigh that. Units with mist between the panes are our misted and failed rooflight replacement work.
When a unit does come out, it is a chance to specify the next one with sound in mind. A laminated acoustic inner pane, a thicker outer pane and firmly seated gaskets are written into the quiet spec that comes with every quote, along with the upstand finish.
More questions about rooflight age
Does a rooflight come with a lifespan written on it?
No. Makers quote a guarantee on the sealed unit, and the terms differ from one product to the next, so read the paperwork for yours. A guarantee period is not a prediction of how long the unit will last, only of how long the maker will stand behind it.
Should I replace the glass only, or the whole rooflight?
If the frame is straight, sound and the right size, a new sealed unit can go into it. If the frame is tired, or the upstand is poor, replacing everything is the better use of the work. Our page on replacing an old skylight sets out the like-for-like and upgrade choices.
Will a new rooflight last as long as the old one did?
Modern units are made with better spacers, coatings and sealants, so there is no reason to expect less. Fitting matters as much as the product, and our guarantee covers the workmanship for ten years.
Is it worth replacing an old rooflight that still works?
Sometimes, sometimes not. It depends on warmth, dryness and noise, and we cover the trade-offs in is it worth replacing a skylight.
If you are unsure how far along yours is, get a quote and we will note the condition of the unit and the upstand at the survey. You can also start from the skylight and rooflight installation overview.