How do I find out what rooflight I have?

Where to look

Open the window and look at the top edge of the sash, or on the frame beside the hinge. On a centre pivot window, rotating the sash brings it into easy view.

It is a small metal or printed label with a code such as MK04 or CK02 alongside a model designation.

Photograph it

Do not transcribe it. The characters are small, some are easily confused, and a mistyped code buys the wrong window. A photograph takes a second and removes the risk entirely.

Send that with a photograph of the window from inside and, if you can do it safely from the ground, one of the roof from outside.

If there is no plate

Painted over, worn away, or removed. Then the opening has to be measured, which means a survey rather than a phone call.

You can help by measuring the visible frame width and height from inside and noting the roof covering: slate, plain tile, pantile or concrete interlocking. That tells us the likely flashing kit before anyone visits.

For flat roof rooflights

Less standardised, and many carry no plate at all. Here the kerb is what matters, and its dimensions have to be measured on site. A price quoted for a flat roof replacement without seeing the kerb is a guess.

Why we ask first

With a photograph of the plate we can usually tell you what it is, whether the size is still made, what the options are if not, and a realistic price, all without anyone visiting.

Find the data plate

Almost every roof window carries a plate or label identifying the manufacturer, the model and the size code. Finding it takes a minute and it answers most of the questions we would otherwise need a visit for.

On a centre pivot window, rotate the sash so the outer face turns inward. The plate is usually on the top edge of the sash, visible once it is turned.

On a top hung window, open it and look at the top edge of the sash, or on the frame beside the hinge.

On a flat roof rooflight, the label is frequently on the frame at one corner, sometimes only visible from outside or in the reveal.

Photograph it rather than transcribing it. The characters are small, several are easily confused, and a mistyped code buys the wrong window.

What the code tells us

The manufacturer and range, which tells us what flashing kits and accessories fit. The size, which tells us whether it is still made or whether we are dealing with an obsolete dimension. And frequently the year of manufacture, which tells us where the unit is in its life.

From that photograph we can usually tell you what it is, whether the size is still available, what the options are if not, and a realistic price, without anyone visiting.

If the plate is missing or unreadable

Common on units that have been painted over, or where the label has weathered away.

Then it comes down to measurement, and that means a survey rather than a phone call, because the dimension that matters is the structural opening rather than what you can measure from inside. Measuring the visible glass or the internal reveal gives a number, and it is not the number the manufacturer works from.

A photograph of the window from inside and outside still helps: the profile of the frame, the hinge position and the flashing type frequently identify the range even without a plate.

Obsolete sizes

Normal on anything fitted before about 2000, and entirely solvable. Three routes: adapt the opening to the nearest current size, which is usually within 40mm or 60mm; find another manufacturer at the old dimension; or reframe entirely.

What nobody should do is force a unit into an opening it does not fit and pack the difference. It survives about a year before the frame goes out of square.

Keep the record

When a new unit goes in, keep the specification with the house paperwork rather than in a drawer. In fifteen years nobody will remember what was fitted, and identifying it again from a plate at height is more effort than filing a piece of paper.

Start with the data plate

A small label on the top edge of the sash, or on the frame beside the hinge. On a centre pivot window, rotate the sash to bring the top edge down to eye level and lock it in the cleaning position. On a top hung unit, open it and look at the frame head.

Photograph it close up with the flash on rather than transcribing it. The characters are small, frequently faded, and several are easily confused, and a mistyped code buys the wrong window.

The plate carries the manufacturer, the model designation, the size code and usually a date. That combination tells a supplier the structural opening, the glazing specification, the operation and whether the size is still current.

If the plate is gone or unreadable

Photograph the whole window from inside, showing the full frame and the way the sash sits, and from outside if that can be done safely. The external cladding profile and the frame proportions identify most mainstream products to somebody who fits them regularly.

Check the other windows on the same slope. On a loft conversion where several went in together, they are usually identical and at least one plate is likely to be legible.

Look for paperwork. The original installation certificate or the sale documents for the house may name it.

The last resort

A survey. Someone who works with these daily will identify the model and size on sight, and can confirm by lifting a tile or two at the head if there is doubt.

On a job of any value, that half hour eliminates the risk of ordering the wrong unit, which is discovered on installation day with the roof already open.