The short answer
Sometimes. A new sash can go into an existing VELUX frame when the maker still supplies a matching one for that model, the frame is sound and square, and the flashing and lining around it are in good order. When the frame is tired, the model is long discontinued or the surround is failing, replacing the whole window is usually the better job.
What a sash swap actually involves
The sash is the opening part: the glass, its frame and the handle and hinge gear. The frame is the fixed box in the roof. A sash swap renews one and keeps the other.
The appeal is obvious. The frame stays put, so the flashing that dresses it into the tiles or slates is left alone, the lining inside is undisturbed, and the plaster and paint in the room are barely touched. Nothing needs to come off the roof except the window itself, which makes it a shorter, tidier visit.
The catch is that a sash only makes sense if a matching one exists. Windows are designed as a pair: a sash that fits a frame from one generation may not sit properly on another. Hinge positions, seal profiles and the way the sash closes against the frame can all differ. So the first job is always the same. Find the data plate, read the code and ask whether a sash for that code is currently available. We explain where the label hides in where is the VELUX data plate, and you should check current VELUX data for what is on offer for your model.
If a match exists, a sash swap can be a perfectly sensible job. If it does not, the window has reached the point where the only clean answer is a whole new unit.
Reasons a sash swap works, and reasons it does not
Two conditions decide it: the state of the frame and the reason you want the change. Go through the table first, then read the paragraph below it.
| Situation | Sash only | Whole window |
|---|---|---|
| Frame sound and square | Good fit | Not needed |
| Timber soft at the base | Poor fit | Better job |
| Flashing old or ill-fitting | Poor fit | Better job |
| Matching sash no longer made | Not possible | The answer |
| Want a different size | Not possible | The answer |
A sound frame is the whole case for a sash swap. Press along the bottom rail and the lower corners with a thumb. Timber that is firm and dry is fine. Timber that is soft, flaking or stained has lost its strength, and a new sash hung on it will only sit as true as the frame does. The same applies to the flashing. If the metal around the frame is tired or was never the right kit for the roof covering, fitting a bright new sash inside it leaves the weakest part of the installation exactly as it was.
The second question is what you want to change. A sash swap puts new glazing into the same opening. It cannot make the window wider, taller or a different type. If you want a bigger unit, or a move from a centre-pivot to a top-hung, the opening itself has to change, and our page on whether a new VELUX fits the old opening covers what that involves.
Glazing, noise and the sash
A new sash is a chance to change what the window does to a room. For a loft bedroom, that can be the most useful part.
The sash carries the glazing unit. If the complaint about the existing window is that it is thin-sounding, draughty or unkind in rain, a new sash with a different glazing build addresses the glass directly. A laminated acoustic pane in a fresh sash, with new seals around it, changes how the room hears aircraft on the Gatwick routes or rain on the slope, without touching the roof covering. The options are set out in VELUX glazing for a quieter loft, and the shorter question of whether an existing window can be upgraded is in can a VELUX be upgraded to quieter glass.
The seals deserve a line on their own. A frame seal that has gone hard and flat lets wind whistle and lets sound round the edge of the pane, however good the glass. New seals come with a new sash, which is part of why the result can feel so different from the outside of the window to the inside.
Whatever we propose, it is written into the quiet spec that comes with the quote. It names the pane build and seals in plain words, so you can see what each part is doing.
How we decide on the day
The decision is made at the survey, with the window in front of us, not from a photograph alone.
- Read the plate. The code tells us the type, size and glazing, and whether a matching sash is currently listed.
- Test the frame. We check for soft timber, movement at the corners and gaps where the lining meets the frame.
- Look at the flashing and tiles. From safe access, we judge whether the dressing around the frame would survive being left as it is for the next stretch of years.
- Ask what you want. Quieter glass, a different opening action or simply a window that works again each lead to a different job.
- Write it down. You get both options priced where both are real, so the choice is on paper.
Sometimes the honest conclusion is that a sash is fine and the window has years left in it. Sometimes the frame is the problem, and putting money into a new sash would be spending it in the wrong place. For how long a typical window lasts, see how long a VELUX window lasts before it needs replacing. The full picture of what we install is on our VELUX window installation page, and you can start a conversation through the quote form.
Sash questions that come up at the survey
Is a new sash cheaper than a new window?
Often the sash alone costs less in materials and takes less time, but only when the frame and flashing are good. If they are not, the saving disappears, because the same visit then has to deal with them. Our costs page explains what drives the price.
Will a sash from another generation fit?
Do not assume so. Sashes are made for a particular frame. Confirm the match against the code and current VELUX data before anything is ordered.
Can I change a manual window to electric by swapping the sash?
That is a different question, because the motor, control and wiring are involved. We answer it in can a manual VELUX be converted to electric.
Does a new sash reset any guarantee?
Our own work carries a 10-year workmanship guarantee. The maker's product cover is separate and worth reading for your model, as we describe in how a VELUX warranty differs from an installer's guarantee.