How long does a rooflight last?

The sealed unit: 20 to 25 years

The first thing to go. When the perimeter seal fails, moist air enters the cavity and condenses where it cannot be cleaned.

Overhead glazing fails sooner than wall glazing: larger daily temperature swings, water sitting on it rather than running off, and more direct UV.

The frame: 30 years and up

A sound timber frame with an intact finish, a polyurethane frame, or a powder coated aluminium one will outlast the glass comfortably. The failures we find are frames where the finish was let go, or where a leak went unaddressed for years.

Moving parts: 15 to 20 years

Hinges, catches, friction stays and gaskets wear. All usually replaceable rather than terminal, and worth replacing rather than replacing the window.

Electrical components: 10 to 15 years

Actuators, control units, rain sensors and batteries. The shortest lived items on the window, and individually replaceable.

What shortens it

Coastal exposure. Real on the Tendring coast. Units at Walton, Mersea or Frinton age faster than the same units at Braintree.

Standing water against the frame from poor drainage.

Neglect. Ten minutes a year on filters, seals and clearing debris genuinely extends the life.

The practical read

If yours went in during the late 1990s, they are due. If several went in together they will fail together, and one visit shares the access cost across all of them.

Twenty five years for the glazing, longer for everything else

The component with a defined life is the sealed glazing unit, and fifteen to twenty five years is the honest range. That is the perimeter seal giving up after decades of daily thermal cycling, not a manufacturing fault.

The frame, the flashings and the structure around the opening comfortably outlast that. On a well fitted installation, replacing the unit at the end of its life is a straightforward swap into the existing opening.

Component by component

Sealed unit: fifteen to twenty five years. Toward the shorter end on a coastal or exposed roof, where the seal takes more thermal cycling, more wind driven water and more salt.

Actuator, on a motorised unit: ten to fifteen years. The shortest lived component, and a serviceable part that unbolts and is swapped for a fraction of the cost of a new window.

Gaskets: fifteen to twenty years, and their life depends almost entirely on whether they are kept clean.

Timber frame, aluminium clad: thirty years and more, because the cladding takes the weather and the timber stays dry behind it.

Timber frame, uncoated or painted: depends entirely on maintenance and exposure.

Flashings: longer than the window, usually, and they should still be replaced with it rather than reused.

What brings the end forward

Standing water, on a flat roof unit. The single biggest factor, and it comes from a kerb that is too low or a deck that does not fall away from it.

A dirty gasket. Grit and moss on the compression seal stop the sash seating properly, which lets water past and makes an actuator work harder on every cycle.

A rigid installation in a moving building. A unit clamped hard into a frame that flexes seasonally is under stress it was not designed for.

Forcing a unit into an opening it does not fit. Packing the difference lasts about a year before the frame goes out of square.

What extends it

A gasket clean once a year, a filter clean, keeping flat roof perimeters clear, and cycling a motorised unit fully a few times a year including in winter.

None of it takes long, and it is the difference between the top of the range and the bottom.

When it goes

Misting between the panes that cannot be wiped off either face. Not a safety issue, nothing is going to fall out of the roof, and it does not improve on its own.

Getting the long end of the range

Ten minutes a year is genuinely the difference between fifteen years and twenty five.

Clean the gasket, because grit on the compression seal stops the sash seating, lets water past and makes an actuator work harder on every cycle. Clean the filter at the top of the sash. On a flat roof unit, keep the perimeter clear and check the outlet the roof drains to.

Cycle any motorised unit fully a few times a year including in winter, because mechanisms that sit unused seize.

And look at the outside every few years and after storms, for lifted flashing edges, slipped tiles or rust staining from a plated fixing.

None of that takes long and all of it is worth doing.

What ends a flat rooflight

Usually the sealed unit, at fifteen to twenty five years, the same as any other. A horizontal unit sits in a harder environment than a vertical window: full sun, greater temperature swings, and on a poorly drained roof, standing water against the perimeter.

On a bonded flat rooflight the glass and frame are one assembly, so when the unit goes the whole thing is replaced rather than reglazed. That is worth knowing at purchase, because it changes the long term arithmetic against a pitched roof window that can be reglazed.

The kerb frequently outlives the unit

Where it is sound, square and insulated, a replacement is a comparatively simple exchange. Where it has rotted, because water has been standing against it or the waterproofing was terminated poorly, the kerb is rebuilt first and the job is considerably larger.

Kerb condition is not visible until the old unit is lifted, which is why a sensible quotation carries a provisional allowance for it.

What shortens it, in order

Standing water. Inadequate fall or falls arranged so water collects beside the unit. This ages the waterproofing, works every joint through freeze and thaw, and keeps the perimeter permanently wet.

Blocked outlets. One autumn of leaves turns a drained roof into a pond.

Foot traffic on a unit not rated for it. The seal and frame give up long before the glass does.

What buys you more years

Get the falls right before it goes in. Keep the outlets clear. Check the perimeter seal annually, particularly at the corners. And do not stand on it.