A roof window is usually due for replacement once the sealed unit reaches 15 to 20 years, and the whole window at 20 to 25 years, sooner on a salt-exposed coastal slope. Age is only a guide though. The real decision comes from condition: misting, rot in the sash, stiff or failed operation, draughts, and parts you can no longer buy.
The age guideline, and why it is only a starting point
Two clocks run on a roof window and they do not run at the same speed. The sealed glass unit is the faster one. Its perimeter seal degrades over 15 to 20 years, the argon fill escapes, and the low-emissivity coating loses performance. The timber frame, the hardware and the flashing are the slower clock, typically good for 20 to 25 years before the window as a whole is worth replacing rather than nursing.
On the Suffolk and north Essex coast both clocks speed up. Salt-laden air off the North Sea holds moisture against the frame between showers, so timber that would last 25 years inland can rot at 15 near open sea. If your window sits on an east or north-east slope at Felixstowe, Harwich, Frinton or Aldeburgh and went in around 2008, it is already in the replacement window whatever it looks like from the ground. We cover why on our coastal frame rot page.
Ipswich has a particular pattern here. A great many roof windows went into loft conversions across the town between 2000 and 2010, during the extension boom, and those units are reaching the end of their sealed-unit life all at once. If yours dates from that decade, it is not too early to look.
The condition triggers that actually decide it
Forget the calendar for a moment. Any one of these means the window is at or past the point of replacement.
Misting or a blown sealed unit
A haze that appears on humid mornings and clears by afternoon is the first sign the perimeter seal has failed. Later it becomes permanent milky staining and mineral tide marks between the panes. Once a unit has blown, the argon has gone and you are heating the loft through the glass. Roof windows blow earlier than wall windows because thermal cycling works them harder: a south slope can swing from below freezing at dawn to over 50 degrees at the glass surface by midday in June. More detail on our misted roof window answer.
Rot in the bottom rail of the sash
This is the trigger that ends the conversation. Older units are laminated pine with an aluminium capping outside, and rot starts at the bottom rail of the sash where water sits. Press it firmly with your thumb from inside. If the timber gives, it has gone, and once rot is in the sash it is generally in the frame too, because the same conditions produced both. A rotten frame is not a candidate for anything but replacement.
Stiff or failed operation
Hinges wear, the friction pads that hold the sash at an angle lose their grip, and the handle mechanism that pulls the sash down onto the gasket stops closing tight. A window that no longer seals draws air, and on an exposed slope, rain. Hardware is sometimes obtainable for units up to about 20 years old. Beyond that it usually is not.
Draughts and cold reveals
A persistent draught around the sash means the gasket has hardened or the frame has moved. A cold reveal with a black mould line at the head, most often in January, is a different fault: a missing or failed insulation collar leaving a cold bridge round the opening. Both point to a window that has reached the end of its service, and a proper replacement with new collars resolves them together.
Discontinued parts
Roof window generations change roughly every 10 to 15 years, and each change moves the frame profile, the hardware fixing points and the glazing bead. Parts for anything older than about 20 years, particularly pre-2000 units, are largely gone: sashes, hinge sets, gaskets, handles and the sealed units themselves. We have opened plenty of 1990s windows on Ipswich terraces where every component is technically repairable and not one is obtainable. That is the honest reason a tired old unit gets replaced rather than mended, and it is the subject of our replace not repair page.
Never go up to check. Everything on this page can be assessed from inside the room, from the sash and the reveal. Diagnosing a roof window from on the roof is not a homeowner job and not worth the risk. If you want the outside and the flashing assessed, that is what the survey is for.
What it means locally, and what to do next
If you are inland at Kesgrave, Martlesham or out towards Stowmarket, corrosion is rarely the issue and the age guideline holds well: watch the sealed unit from 15 years and the whole window from 20. On the coast, bring both forward. In the older conservation villages the same triggers apply, but the replacement often has to be a recessed conservation-style unit to keep permission, which changes the specification rather than the decision to replace.
Whichever applies, a like-for-like replacement is a one-day job because the structural opening stays exactly as it is. If the sealed glass has misted on a young window with a genuinely sound frame, that is the one case worth weighing against a full swap, and we set out that test on our misted glazing page.
A quick replacement checklist
- Sealed unit fitted 15 or more years ago, or any visible misting between the panes.
- Whole window 20 or more years old, or 15 or more on a coastal slope.
- Bottom rail of the sash gives under thumb pressure.
- Sash is stiff to open, will not hold position, or no longer pulls down tight.
- Persistent draught around the sash, or a cold, mould-prone reveal.
- Parts or a matching sealed unit are no longer available for the model.
Tick two or more and it is time. Send us a photograph of the window from inside and one of the roof from the garden, or read the fuller picture on our roof window installation hub.
Request a fixed quote for a like-for-like roof window replacement in Ipswich, Suffolk or north Essex, and we will confirm the exact figure after survey.
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.