How long does a roof window last?
Twenty to twenty five years is the working figure for the sealed unit, and that is normally what ends a roof window’s life. The frame usually has more left in it than the glass does. The flashing, if it is lead and it was dressed properly, will still be sound when both have been changed. So the answer depends entirely on which component you are asking about, and they do not wear out together.
What shortens all of them is the same short list: exposure, moisture, orientation and the quality of the original fitting. A window on a sheltered north facing slope in a dry loft will comfortably outlive one of the same model on an exposed south west plane over a bathroom. The installation detail behind that is covered under VELUX window installation.
What actually reaches the end first
In practice, the sealed unit. Misting between the panes is the single most common reason a roof window comes out, and it is a failure of the edge seal rather than of the glass or the frame.
Second is the frame surface: on timber units, the lacquer or paint film breaks down, water gets into the wood and the sash swells until it stops closing cleanly. Third, some distance behind, is the mechanism, where hinges and friction stays go stiff or slack. Fourth is the flashing, which on lead is usually the longest lived part of the assembly. Knowing that order is useful, because it tells you what to look at first.
The sealed unit, and how its life is spent
A double glazed unit is two panes held apart by a spacer bar, with a primary and secondary seal round the edge and a desiccant inside the spacer that absorbs the small amount of moisture in the cavity.
Every day the cavity heats and cools, the gas expands and contracts, and the seal flexes. Eventually it lets moisture past faster than the desiccant can take it up, the desiccant saturates, and water condenses inside the cavity where nothing can reach it. That is the misting, and it is terminal for that unit. In a roof plane the cycle is harsher than in a wall, because the pane faces the sky and the temperature swing across a clear night is wider.
Timber frames, and the moisture that shortens them
Most roof windows fitted in Essex before about 2010 have a laminated pine frame with a clear lacquer or a white paint finish inside. Well kept, that frame will run past thirty years. Badly kept, it will be soft at the bottom corners in fifteen.
The failure is always at the sash bottom rail and the corner joints, because that is where condensation runs down the glass and collects. The maintenance is a light sand and a fresh coat of the manufacturer’s lacquer every four or five years, which takes an hour a window and is almost never done. Whether it is worth doing on an older unit is a judgement about the glass as much as the wood, and there is more on upkeep under whether roof windows need servicing.
Polyurethane and clad frames, and how they age
Modern units come in two other constructions. Polyurethane frames have a timber core wrapped in a moulded polyurethane skin with no joints at the corners, so there is nothing for water to get into and no coating to break down. In a humid room they are the sensible specification and they age very slowly.
Aluminium cladding on the outer face is a separate question and now close to universal. The cladding takes the weather and ultraviolet, the timber behind it stays dry, and a polyester powder coated finish holds its appearance for decades. A clad timber unit and a polyurethane unit will both outlast the glass in them, which shifts the whole conversation onto the sealed unit.
Mechanisms, and the years they give
Hinges, friction stays, the handle and the locking cam are steel and plastic components under repeated load. On a window opened daily they are the parts that show wear first, and on a window opened twice a year they will outlast everything else.
Symptoms are recognisable: a sash that will not stay where it is put, a handle that needs pressure to latch, a rotation that binds partway. Most are adjustment rather than wear. Where genuine wear has set in, hinges and stays are available as parts for current generations and become difficult to source somewhere past twenty years, which is usually about the point at which the glass is asking the same question.
The flashing, and the part that outlives the rest
Lead is the outlier. A code four or five lead apron and side soakers, dressed by hand and correctly lapped, will run sixty years or more, and it is entirely normal to take an old window out and find the lead around it in better condition than anything it was weathering.
The aluminium flashing kits supplied with modern units are shorter lived but still measured in decades, and their weak point is the sealing strip at the head rather than the metal. Either way, the flashing gets renewed when the window is exchanged rather than because it has failed, because the new frame is a different profile and wants its own matched kit.
Orientation and exposure, and the years they add or take
Two windows of the same model on the same house can differ by five years or more in working life, and the difference is which way the slope faces and what stands around it.
| Condition | Effect on the sealed unit | Effect on a timber frame |
|---|---|---|
| North facing, sheltered | Gentle cycling, long life | Slow coating breakdown, more condensation |
| South or west facing | Wide daily temperature swing, seal works harder | Ultraviolet degrades the finish faster |
| Coastal, Blackwater and Canvey | Salt film on the outer pane | Salt attacks fixings and finishes |
| Over a bathroom or kitchen | Little effect | Persistent moisture, shortest frame life |
| Under mature trees | Debris holds water at the perimeter | Damp shade, quicker coating failure |
Installation quality, and the years it is worth
The single biggest variable is not in the catalogue. A frame set square and out of wind closes evenly on its gasket for its whole life. A frame set twisted loads one corner of the sash, distorts the gasket, and lets driven rain into the rebate from the first winter.
The same goes for the underlay collar dressed into the frame, the flashing laps run the right way, and the drainage slots left clear. None of the four is visible once the covering is back on, all four are cheap to get right on the day and expensive to sort out afterwards, and that is exactly why the workmanship carries a ten-year guarantee rather than the sales pitch resting on the brand of glass.
Knowing when an exchange is due rather than overdue
Four signs, in the order they usually appear. Misting or a permanent haze between the panes. A sash that no longer holds its position or needs force to latch. Timber that is soft or dark at the bottom corners of the sash. And daylight visible around the edge of the internal lining, which means the frame has moved relative to its trimming.
Any one of those on a unit past twenty years points the same way. A like for like exchange into the existing opening is often a single day’s work and a good moment to upgrade the glass, since the labour is committed anyway. Where the room has changed use since the window went in, it is also the moment to consider a larger opening, covered under replacing a roof window with a bigger one.
Tell us about your roof
We start with the building, the covering and the slope. Then we tell you what will suit it, and what it will cost, as a fixed written number.
- Surveyed before it is priced
- 10-year workmanship guarantee
- Building Control notification handled
- New installations and replacements