How Long Do Roof Windows Last?

The window is several parts, not one

A roof window is an assembly. The frame is fixed to the rafters. The sash is the opening part, carrying the glass. The sealed unit is the double or triple glazing, two panes bonded around a spacer with a gap between. Rubber or foam seals sit between sash and frame. And around the outside, the flashing kit ties the window into the roof covering. Each of these has its own working life, and the weakest decides when the window is in trouble.

This is why asking how long a roof window lasts is like asking how long a car lasts. The body may be fine for decades while tyres, brake pads and batteries come and go. The roof window frame is the body; the seals and glazing are the wearing parts.

What typically fails first

The seals harden and crack as the rubber ages in sun and frost. Once they stop making a tight seal, the window leaks air, rattles and can let water past the sash. Replacement seals are available for many models and are a modest, quick repair. The glazing unit can fail in its edge seal, letting moist air in between the panes. The sign is permanent misting that wipes off neither side. A failed unit loses its insulating performance and looks poor, and it can be swapped on its own, as our glass-only answer sets out.

The flashing is another weak point. It is metal or a plastic composite fitted around the frame, and it ages with the roof covering. A poorly fitted flashing leaks within a few seasons, and a good one outlasts the tile. Sealants applied around windows to patch problems tend to dry out and crack, and they are a short-term fix. When a window leaks, the cause is more often the flashing or the seals than the glass, a point explored in the guide to leaking roof windows.

Frames and finishes

Timber frames, usually pine with a protective coating, last well if the coating is intact. Exposure, condensation and a damaged finish let moisture in and start rot, so a timber window kept dry and sealed does better than a damp one. Aluminium cladding on the outside protects the timber from weather. Plastic-coated and PVC frames resist rot but can fade and warp in strong sun. A frame that has rotted at the bottom corners is a sign of long-term water, often from condensation or a leak at the flashing.

Hardware matters too. The hinges, pivots, handles and springs wear with use. A stiff window that will not stay open or close properly may need new parts, not replacement. See also the answer on why a roof window will not close.

What shortens a roof window's life

Poor installation is the leading one. A window fitted without the right flashing for the covering, with a broken tile near the frame or with no underlay collar, will leak early. Constant condensation, caused by poor ventilation in the room, rots the frame from within. Strong sun and heat age the seals and coatings, so a south-facing window ages faster than a north one. Debris and moss clog the channels around the frame and hold water. Slamming and stiff operation wear hinges. Pressure washing can drive water past the seals.

Looking after one

Clean the glass and wipe the seals twice a year. Keep leaves and moss from the flashing and the drainage channel above and around the frame. Look at the timber and its coating each year, and repaint or re-coat bare spots. Lubricate moving parts with an appropriate product from the maker. Our article on how to clean a roof window covers the routine. Act on small things quickly, such as a damp stain below the window, as that is the earliest warning.

Repair or replace?

If the frame is sound and the problem is seals, glass or flashing, repair is normally sensible. If the frame has rotted, the unit is very old, or the window does not meet current thermal standards, replacement may be better. A new unit also brings improved glazing and a new flashing kit, and the guide on replacing an old roof window covers the process.

On a visit we look at the frame, seals, glass and flashing, take pictures for you and say whether a repair will do. If the window has years left, we say so. The written quote is a fixed figure, and the rest of our glazing work sits under roof windows and skylights.