The answer
How long do skylights last depends on the parts rather than the glass. The sealed unit's edge seal is often the first part to show age, then the gaskets and the paint on a timber frame, and last the flashing or the kerb covering around it. One tired part does not mean the whole unit is finished, and a survey separates the two.
Which parts give out first
A skylight or rooflight is several components working together, and each ages at its own pace. The glass sheet itself changes very little over time. What wears is what holds it and what keeps rain out around it.
- The sealed unit. The sealant at its edge is stretched every day by heat and cold, and when it lets go the unit mists between the panes. The cause is set out in why rooflight glass mists.
- Gaskets and beads. The rubber or sealant strips that hold the glass in its frame harden and shrink, and the first sign is often a draught or a stain at the edge.
- The frame. A timber frame needs its paint or varnish to stay intact, and bare wood takes in water. Aluminium and uPVC frames wear more slowly but have gaskets and hinges of their own.
- The weathering. Flashing on a pitched roof and the kerb covering on a flat one, in felt, rubber or GRP, are exposed on the outside and are renewed on their own timetable, sometimes before the glass.
The life of the assembly runs to the first part that fails, and to how hard that part is to get at.
Signs that a part is tired
A skylight tends to give notice before it fails. A few signs are worth knowing, and each points to a different part:
| What you see | The part it points to |
|---|---|
| A haze or droplets between the panes | The edge seal of the sealed unit |
| A draught or a hiss round the sash | Gaskets that have hardened or shrunk |
| Flaking paint or soft timber | The frame, where water has been getting in |
| A stain on the ceiling by the opening | The flashing, the kerb or the lining |
| A sash that sticks or will not stay open | The hinges, stays or a frame that has moved |
A stain beside the rooflight deserves attention first, since water reaching the ceiling or the timber does damage that outlasts the glass. Mist between the panes is gentler: it costs warmth and clarity, and it can be dealt with when the work suits the room. Wipe-away condensation on the room side is a separate matter, covered in why a rooflight gets condensation on the inside.
A tired part or a finished unit
The useful question is whether the rest of the unit is still sound. If one component has aged and everything else is in good order, the unit can be brought back into service by replacing that component: a new sealed unit in a frame that is solid, for example. If several parts have gone at once, or the frame is soft, the unit has reached the end of its life and the sensible answer is a new rooflight.
Three tests help to tell the two apart:
- Press the timber of the frame with a thumbnail along the bottom edge and at the corners. If it gives, the frame is failing.
- Look at the covering round the base of the kerb or the flashing, from a window or a ladder at the eaves. Cracks, lifted edges and gaps mean the weathering has aged with the glass.
- Compare the age of the unit with the work it has done. A unit on a south-facing slope in full sun, or one that has had water standing against it, has worked harder than one in shade.
A survey puts those findings together. When the answer is a new sealed unit, the cost and the route are in what moves the price of replacement glass. When it is a new rooflight, there is the chance to change its size or position, as described in using a failed rooflight to improve a room.
What keeps a skylight going
A few habits lengthen the life of what is already there, and none of them needs time on the roof itself.
- Clean the glass with water and a soft cloth. Harsh abrasives and strong solvents can mark coatings and attack sealants.
- Keep gutters and the roof around a flat rooflight clear of leaves, since water that lies against the kerb or the edge of the glass ages the sealant faster.
- Repaint or re-varnish a timber frame before the finish opens, and keep the drainage slots in a window frame clear.
- Look at the ceiling beside the opening now and then. A new stain or a patch of flaking paint is the earliest warning you will get.
None of this makes an old unit last for ever, and a manufacturer's own guarantee covers the product for a set period that differs from one to the next. What we guarantee is the fitting of a new unit, for ten years, in the terms on our guarantee page; it says nothing about how long the glass itself lasts. The roof the unit sits in is covered on the misted and failed rooflight replacement page.
If a rooflight in your house is showing signs of age, a free survey will tell you which part has gone. Send a message through the quote form and name the room it lights.