The short answer
A roof window has several parts that age at different rates, so there is no single answer. The frame can outlast the sealed glass unit, and the seals and flashing are the parts most likely to need attention first. Makers give no lifespan promise worth relying on, and a warranty describes cover, not lifespan. A survey of the window you have shows how much life is left and whether to repair or replace it.
How the frame, glazing, seals and flashing each wear, the signs a window is tiring, and when repair is the better buy.
Frame, glazing and seals
A roof window is an assembly, and each part ages in its own way. The frame is the longest-lived part when it is kept sound. Timber frames need their coating kept up, and the finish on a window in full sun or exposed to driving rain wears faster than one on a sheltered slope. The sealed glazing unit is a different case, because the seal around its edge slowly gives way and lets moist air in.
Rubber and foam seals around the sash perish with sun and temperature swings. They go hard, flatten or crack, and the window starts to let in draughts and rain. Hinges, handles and the opening mechanism also wear with use, especially on a window that is opened every day.
Use is as important as age. A window in a bathroom lives in humid air, and a window facing the prevailing weather takes more punishment. Beware of any blanket figure for life. Warranties describe what a maker will fix, not how long a window will last, and the same is true of any guide: it describes a range for typical cases, not a promise for your roof. Our roof windows and skylights page covers the work we do on each part.
Signs a window is wearing out
The signs are usually easy to spot if you look. Misting between the panes, or a milky haze that does not clear, points to a failed sealed unit. A sash that no longer closes flat, a handle that is loose, or a draught on a windy night points to worn seals or a hinge issue. A sash that sticks or will not shut flat is worth a roofer's look.
Water is the bigger warning. Drips, a brown stain on the lining or a damp patch on the ceiling mean water is getting round the frame, and the usual culprit is the flashing or its seal, not the glass. Read our guide to a Velux window leaking before assuming the whole unit has to go.
Outside, look from the garden or a safe vantage point. Cracked or lifted flashing, slipped tiles beside the frame and moss collecting on the top edge all shorten the life of what lies underneath. Never climb on the roof to look. A roofer can inspect the window and the covering around it and show you photos of the problem.
Repair or replace?
Repair is the better buy when only one part has failed and the rest of the window is sound. Checkatrade's July 2026 repair guide gives £165 to £1,050 for a Velux repair and £1,000 to £2,500 to replace the whole window like for like. Those are typical national ranges, not Crown prices, but they show the shape of the decision: a repair that approaches the cost of a new window is hard to justify.
Replacement glass is the usual middle route when the sealed unit has failed but the frame is good, and our answer on Velux replacement glass explains how it works. New flashing alone can cure a leak on a window that is otherwise fine. If the frame is rotten, the sash is distorted or the window is too small for the room, replacement is the sensible choice.
Age is not a reason in itself. A well-kept older window may have years left, while a badly fitted newer one may leak from the first winter. Our survey checks the window, flashing and opening, and we send photos with a single written total for the repair and another for the replacement, so you can choose on the evidence.
Making a window last longer
A little care goes a long way. Keep the glass and frame clean and dry, wipe away condensation and open the ventilation bar so moisture does not sit on the frame. Our answer on condensation on a Velux window covers the inside.
Keep the roof around the window in good order. Clear moss and leaves from the top edge, where they hold water against the flashing, and have slipped tiles beside the frame put back quickly. If the gutter above overflows onto the window, fix the gutter. Wooden frames need their finish renewed on the maker's schedule, before the bare timber starts to take on water.
Last, plan a window's replacement alongside other roof work if you can. When a roof is being re-covered, the flashing around every window needs to come out anyway, and fitting new windows in the same visit saves access costs. Ask for the plan to be written into the price, so each window's condition is recorded before the covering goes on.
More on this in Velux Roof Windows & Skylights in Crawley
Two more lifespan questions
Is an old roof window worth keeping?
Often, if it still opens and closes freely, the glass is clear and there is no water getting in. Age by itself is not a fault. Have it checked before a new roof goes on, because the flashing is renewed then and the window can be assessed at the same time.
Does a Velux warranty tell me how long it will last?
No. A warranty states what the maker will put right, for how long and under what conditions. It is not a forecast of life, and it can exclude damage from poor fitting or lack of upkeep. Read the terms, and keep the invoice and any installation record safe.