The answer
Open the window and look along the top of its frame: VELUX says the data plate is fixed there, with the size code printed on it. The letters give the width and the digits give the height, so a code such as MK04 describes a window 78 cm across and 98 cm tall. Blinds, a like-for-like replacement and the flashing kit are all ordered against that code.
Where the plate sits
The plate is not visible from the floor with the sash shut. Swing the sash to its normal open position and the top edge of the frame comes into view, which is where the maker places the label. With a frame set high in the loft roof, a stool and the torch on a phone beat reaching blind. Paint and lining plaster can crowd the label, so scan the full width of the frame before deciding it has gone. Everything here is done from inside the room, and nobody needs to go near the roof.
Reading it in four moves
- Open the sash Use the handle, the rod or the remote, and let it settle in its usual open position.
- Look at the top of the frame The label is on the frame itself, not on the glass or the sash.
- Take the letters, then the digits The first part names the width and the figures after it name the height.
- Photograph it square on Close enough that every character reads clearly on the screen.
Reading the letters and the digits
Think of the code as a short description of the window's shape. The letters at the front stand for its width and the digits that follow stand for its height. Take MK04 from our example: that is a window 78 cm across and 98 cm tall. The same logic applies to any other VELUX code you meet, though this page quotes only the one measurement we can vouch for. A different letter or different digits mean a different width or height, and a tape measure confirms it at survey.
Why a blind asks for the code
A VELUX blind is cut for a particular window size and made by the same maker. A blackout blind for a code you guessed at can hang short or sit proud of the frame, and may not clip into its brackets. Give the supplier the exact code and the blind is made for the frame. If the window is old, quote the make as well, since blinds from different makers do not swap. Once you know the size, blinds and controls sets out the fabrics and how each is worked.
Why a swap asks for the code
A new window of the same code is made for the opening the old one occupies. That keeps the rafters and the trimming where they are, and can leave the inside lining alone too. The code also guides the choice of flashing kit, the collar that keeps rain out at the frame edge, though the roof covering has the final say on which kit goes in. Our replacing an old VELUX window guide follows that job from first look to handover.
| Item | Matched to |
|---|---|
| Blind | Size code and maker |
| Replacement window | Size code, so it fits the opening |
| Flashing kit | Size code and roof covering |
| Lining, if it changes | Opening, checked at survey |
Putting the code to work on a quote
When two firms price the same job, the figures only compare if the windows match. Ask each one to write down the code and the type it has in mind. Quotes that look far apart can turn out to describe two different windows, and the code shows it at a glance. It is also the one detail a blind supplier will ask for before anything else, so keep the photo of the plate somewhere you can find it.
When the plate has gone
Labels fade, get painted over or disappear behind a re-plastered lining. The survey then takes the frame and the opening in hand and works backwards to the code. The photo is still useful: a picture of the whole window, the frame and the roof outside gives a head start. Send it by WhatsApp to 07880 284133 before the visit. A figure never comes from a photo by itself: the plate settles size, and the survey settles everything else.
What the code leaves out
Matching codes do not make matching windows, since one may open differently, carry other glass or date from another year. The code is a size, so it cannot tell you whether a rooflight sits in your slope as a manual, electric or solar model. Other makers use sets of codes of their own, which do not line up with VELUX letters. Treat the code as the start of a conversation about the skylight, with the survey checking the rest.
The plate gives you the size; the survey gives you everything else.