If your roof window was fitted before about 2005, it is almost certainly an obsolete generation and the parts for it are no longer made. The short answer to the question people ring us about: an obsolete VELUX window replacement is the only route, because the frame profile, the hardware fixing points and the glazing bead all changed at each generation change. A sash from a current unit will not mount to a 1998 frame. What does carry over is the size code, which means a modern window almost always drops into the structural opening you already have, without touching a rafter.
That is the good news buried inside the bad. The unit is finished, but the hole in your roof is fine.
Read the data plate before you do anything else
Everything about an obsolete unit is decided by four pieces of information, and all four are stamped on a small plate on the top edge of the sash. Open the window, rotate the sash to the cleaning position and lock it there, then look at the upper frame member of the sash itself rather than the fixed frame.
You are looking for:
- The model designation. A short alphanumeric code identifying the range and the operating type. This is what tells us which generation you have, and it is the single most useful character string on the plate.
- The size code. Two characters, a letter for width and a number for height. MK06 is a 780mm by 1180mm structural opening. This has been broadly stable across generations, which is why replacement is usually straightforward. Our guide to size codes goes through the full set.
- The year of manufacture. Often printed as a four-digit year, sometimes as a week and year. This is the number that determines parts availability, and it is frequently the only thing still readable on a sun-cooked label.
- The serial number. Useful for confirming exactly which production run a unit came from where the model designation is ambiguous.
Photograph the plate rather than transcribing it. Handwritten transcriptions of a faded label go wrong roughly one time in four, usually by confusing a zero for an O or an eight for a six, and the wrong size code means the wrong window arrives on a Tuesday morning. If you cannot reach the plate safely, stop. Do not go onto the roof and do not stand on furniture to reach a window above head height. We read the plate at survey, or we measure the structural opening directly.
What to do when the plate has gone
On south-facing slopes the label frequently bakes into illegibility, and on units from the early 1990s it is often absent entirely. That is not a problem. At survey we measure the structural opening from rafter face to rafter face and from trimmer to trimmer, then match to the nearest current size code. What we do not do is order from a homeowner’s tape measurement of the visible frame, because the visible frame is not the opening and the difference is around 40mm a side. Our page on finding the size code covers the exact procedure.
Why parts for a discontinued range dry up
Roof window generations change roughly every ten to fifteen years. Each change is driven by thermal performance requirements, glazing thickness and manufacturing method, and each one moves three things that matter enormously for spares:
- The frame profile. The cross-sectional shape of the timber and the aluminium capping over it. Change this and nothing that clips, screws or slides onto the old profile fits the new one.
- The hardware fixing points. Hinge plate positions, screw centres and the recesses machined into the timber to receive them. A hinge set is not a generic part. It is machined to sit in a specific mortice at a specific height.
- The glazing bead. Which in turn sets the sealed unit thickness. When the glass goes from 18mm to 24mm to accommodate a low-emissivity coating and an argon fill, the bead and the rebate both change, and the old sealed unit becomes a component nobody makes.
Manufacturers typically carry spares for a discontinued range for a while after it leaves production, then wind them down as the tooling is retired. Independent stockists hold residual inventory for a few years beyond that. After that there is nothing but salvage, and salvaged parts from a window of the same age are the same age.
| Era of manufacture | Parts availability | What a replacement involves |
|---|---|---|
| Pre-1990 | None. Tooling long retired, no residual stock, salvage only | Straight swap into the existing opening in most cases. Frame depth and lining detail will differ, so a modern lining kit is normally needed |
| 1990 to 1999 | Effectively none. Occasional salvaged sashes and handles, no gaskets, no sealed units | Like-for-like into the existing opening. Expect the trimmers and underlay to need attention once the old unit is out |
| 2000 to 2009 | Very limited. Some handle assemblies and friction pads, rarely a sealed unit, no sashes | Like-for-like. This is the bulk of the replacement work we do around Ipswich |
| 2010 to 2017 | Partial. Hardware and some gasket sets still surface, glazing usually not | Like-for-like, generally the cleanest swaps because the opening and reveal detail are close to current |
| 2018 onward | Current or one generation back. Most components still catalogued | Rarely a replacement candidate unless there is impact damage or a fitting fault |
Eras are approximate and overlap. Two windows fitted the same week can sit either side of a generation change if they were bought from different stockists clearing different inventory.
Which components go first
Failure order on an obsolete unit is predictable, and knowing it tells you how much life is left before the window stops closing properly.
Gaskets and weather seals
The perimeter gasket that the sash pulls down onto perishes first, usually somewhere between twelve and eighteen years. It hardens, then it compresses permanently, then it cracks at the corners. The symptom is a whistle in an easterly and a cold draught down the reveal. Gaskets are extruded to a profile, and the profile is generation-specific, so once the range is gone the gasket is gone.
Handle assemblies and friction pads
The handle does two jobs. It latches, and it pulls the sash down onto the gasket with enough force to compress it evenly all round. Friction pads hold the sash at an angle when open. Both are wear items. Handles are among the last components to remain available for a discontinued range, which is why you occasionally find one for a 2006 unit and never one for a 1996 unit. If the handle is the only thing wrong with a window from the last ten years, that is a different conversation, and our page on a roof window that will not close covers it.
Hinge sets
Pivot hinges carry the full weight of the sash through every rotation, and on a centre pivot that is a lot of cycles over twenty years. Worn hinges let the sash drop a few millimetres, which throws the gasket compression out on one side and starts a slow leak at a top corner. Hinge sets are machined to the generation. There is no universal replacement.
Sashes
Once the sash timber goes, the window is finished. Sashes for discontinued generations are not manufactured and salvaged ones are the same age as yours. Rot in the bottom rail of the sash is the most common terminal diagnosis we give, and we have written it up separately on our rotten roof window frame page.
Sealed units
Misting is the failure most people notice first, and it is the one that produces the most disappointed phone calls, because the obvious fix appears to be new glass. On an obsolete unit it is not available: the glass thickness and bead detail changed with the frame. Even where a unit can be made to size, it is being fitted into a twenty year old frame with a perished gasket and worn hinges. The reasoning is set out on misted roof window glazing.
We do not source or fit spares. Apex does not carry out component work of any kind on roof windows: no glass swaps, no gasket sets, no handle assemblies, no resealing. This is not a policy designed to sell more windows. It is that by the time a unit is old enough to need parts, the parts have gone and the timber and flashing beneath it have been wet for several winters. We diagnose honestly and we replace.
The pre-2000 units on Ipswich terraces
There is a particular category of job we see repeatedly on the Victorian and Edwardian terraces off Norwich Road, Spring Road and around the town centre. Roof windows fitted in the late 1980s and 1990s, usually a single unit over a stairwell or into a small back bedroom, natural slate covering, shallow pitch.
Open one of those up and every single component is technically serviceable. The timber is often better than modern laminated pine because it was slower grown. The aluminium capping is sound. The hardware is heavy and well made. And not one component is obtainable, because the range left production before the current millennium and the tooling went with it.
That combination is genuinely frustrating and it is worth naming plainly. It is not that the window is beyond fixing in principle. It is that the supply chain that would allow it stopped existing about twenty years ago, and no amount of goodwill on our part changes that. We wrote a separate piece on why an old roof window is replaced rather than patched because it comes up on nearly every survey of a pre-2000 unit.
Why the replacement is usually simpler than people expect
Because the size codes have been broadly stable, a modern unit is specified to fit the structural opening you already have. The rafters are not touched. The ceiling reveal stays where it is. Building Control involvement is limited to the thermal element requirement under Part L rather than anything structural.
Two things do change between an obsolete unit and a current one, and both are finishing questions rather than structural ones.
- Frame depth. Modern units are deeper front to back to accommodate thicker glazing and better thermal breaks. The frame therefore meets the plasterboard reveal at a different point, which is solved with a modern lining kit rather than by rebuilding the reveal.
- Flashing height. The flashing kit is matched to your covering and to the current frame, so the old kit comes off and a new one goes on. The old kit is twenty years old regardless and reusing it would be the false economy that starts the next leak.
The upgrade is not trivial either. A sealed unit from 1998 started life around 3.0 W/m²K and has lost its cavity fill since. A current unit sits near 1.1 to 1.3. On a north-facing loft bedroom that is a noticeable difference in how hard the room is to heat in February. The full sequence is on our like-for-like replacement page, and the process detail on how we fit it.
What it costs
A like-for-like replacement of an obsolete single unit up to MK06 runs £1,150 to £1,650 supply and fit, including the flashing kit matched to your covering, the insulation collar, the underfelt collar and reinstatement of the roof covering. PK10 or larger runs £1,450 to £2,100. Two units on the same slope, £2,000 to £2,900. Scaffold on a terrace is the biggest single variable and is quoted separately. Full figures are on roof window installation costs.
Common questions about obsolete roof windows
How old does a roof window have to be before it counts as obsolete?
Practically, anything made before about 2010 has limited parts availability and anything before 2000 has effectively none. Generations turn over every ten to fifteen years, and spares wind down within a few years of a range leaving production. A window from 2004 is not old for a building component, but it is two generations back for a manufacturer, and that is what decides whether anything fits it.
Can I get a sealed unit made to size for an old roof window?
A glass merchant can cut a double glazed unit to almost any dimension, but that is not the constraint. The glazing bead and rebate depth changed with the frame generation, so a unit made to the old glass size will not bed and bead correctly in a frame designed for different glass. We do not carry out glazing work on roof windows in any case, and on a unit old enough to have blown, the gasket and hinges are at the same point in their life.
The plate on my window is unreadable. Can you still quote?
Yes. We measure the structural opening at survey, from rafter face to rafter face and trimmer to trimmer, then match to the nearest current size code. Missing or illegible plates are normal on pre-2000 units, particularly on south-facing slopes where the label has been cooked. Do not climb up to look for it yourself. Send a photograph from inside the room and one of the roof from the garden showing the covering, and we will take it from there.
Will a modern window fit the hole my old one came out of?
Nearly always, yes. The size codes are structural opening dimensions and they have been broadly stable for decades, so a 780mm by 1180mm opening from 1996 takes an MK06 today. What differs is frame depth, which changes how the frame meets the internal reveal, and that is handled with a modern lining kit. The rafters and trimmers stay as they are unless we find rot in them once the old unit is out.
Do you sell parts if I want to sort it out myself?
No. We do not source or fit spares for roof windows and we hold no component stock. For a unit still in current production a stockist can supply hardware directly. For a discontinued range there is generally nothing to buy, which is the whole problem. We also would not advise anyone to work at height on their own roof to fit a part, whatever its age.
My old window still works perfectly. Should I replace it anyway?
Not on age alone. If the sash pulls down evenly onto the gasket, the timber is firm at the bottom rail and the glass is clear, leave it. What we would say is that once a component does fail on an obsolete unit, there is no intermediate step available, so it is worth knowing the replacement figure in advance rather than discovering it in the middle of a wet January. Our page on when to replace a roof window sets out the specific triggers.
Get a fixed price
Send a photograph of the data plate if you can reach it safely from inside, a photograph of the window from within the room, and one of the roof taken from the garden showing the covering. That is usually enough to tell you whether a like-for-like replacement is possible and roughly what it costs before anyone comes out. Then we survey, confirm the opening and the flashing kit, and issue one written price that does not move.
Our installers have 25 years fitting VELUX, Keylite and Roto roof windows. We are not part of any manufacturer’s approval scheme and we do not claim to be. Every installation carries a 10-year workmanship guarantee.
Request a fixed quote, or go back to VELUX window installation for the full picture.
Thinking about this job? We survey across Ipswich, Suffolk and north Essex and give you a fixed price before any work starts, with a 10-year workmanship guarantee.