Why one window has no single lifespan
A roof window is several parts working together: a frame, a sash, a sealed glass unit, rubber or foam gaskets, hinges or pivots, and the flashing that links it to the roof. Each one ages at its own rate, so asking how long the whole window lasts is a bit like asking how long a car lasts. Some parts are renewable and some are not.
Position matters too. A window on a south-facing slope takes more sun on its seals and paint. One on an exposed slope takes more driven rain and wind. A window above a bath or kitchen sees more moist air, which tests the finish on the inside frame.
A warranty and a lifespan are not the same measure. A warranty is a promise about defects for a set period; it does not tell you how long the window will keep working once the period ends. The useful question is which part is wearing and what it is telling you, and the rest of this page is about that.
The parts that wear first
On a roof window, a handful of parts can give trouble before the frame itself does. Each one below comes with the sign that gives it away, so you know what to look for from the room:
- The edge seal of the double-glazed unit, which lets moisture in and shows as misting between the panes.
- The gaskets and weather seals round the sash, which flatten, harden or split.
- The hinges, pivots and balance mechanism, which stiffen with wear and grit.
- The finish on the frame, which fades or flakes where it meets the weather.
- The flashing at the edges, where the sheet metal or moulded kit joins the tiles.
The glass itself rarely wears out. What fails is the way it is held and sealed. A window can look sound from the garden and still be damp inside, which is why a look from the loft tells you more than a look from outside.
The flashing is the part that depends most on the covering around it. Our page on the flashing kit explains how it is built and fitted.
Signs that a window is near the end
Look for patterns rather than a single mark. A damp patch that appears once after a storm may be the covering. One that returns every time the wind blows from the same direction points at the window opening.
- Misting or water droplets between the panes: the sealed unit has failed.
- A brown ring or bubbling paint on the lining below the window.
- A draught round the closed sash, or a sash that no longer shuts flat.
- Rust or white powder on the flashing, or a gap between flashing and tile.
- A handle or hinge that grates, sticks or needs force.
Condensation on the room side of the glass is a different problem from a leak. It is damp room air settling on a cold surface, and ventilation can improve it. Our guide to roof window condensation sets out how to tell the two apart.
Damp that sits behind a lining stays out of sight, so a check from the loft side is worth making early. Note the date and the weather when a stain appears, because the pattern helps a roofer find the cause.
Replacing the window in the same opening
When the frame and sash are worn out, the usual answer is a new window in the same opening. The roofer lifts the covering round the old window, removes the frame and flashing, checks the timbers underneath, and fits a new frame and kit. Where the new window matches the old in size, the rafters and trimmers often stay as they are.
The things worth checking before ordering are:
- The size of the existing opening, measured between the frame edges.
- The condition of the timbers around it, including any staining or softness.
- The covering, so the new kit matches the tile or slate.
A replacement window is a new element, so it has to meet the Building Regulations window row in Approved Document L, set at a figure of 1.4 or Window Energy Rating Band B. A failed glazed unit alone may be cheaper to treat than the whole window, which our page on replacing roof window glass explains. The wider range of work is on the roof windows and skylights page.
