How do I find out what rooflight I have?
Nearly always from a plate on the sash, reachable from a stepladder in the room, carrying the make, a product code, a size code, a glazing code and a manufacture date. Twenty minutes with a stepladder and a phone camera is usually the whole exercise, and the photograph you come away with is enough for somebody else to identify the unit, name a current equivalent and give you an indicative figure without setting foot in the house. Where the plate has been painted over, and on a lacquered pine sash from the eighties it frequently has, there are four other routes and they work in a sensible order. Flat roof units are the awkward case because most of them never carried a plate at all. What the codes mean once you have them, and how they map from the old three-digit system to the current one, is on the replacing a failed or misted rooflight page. This one is about getting to the information in the first place.
Getting to the plate safely, which takes longer than reading it
Everything below happens from inside the room and none of it needs anybody on the roof. Use a proper stepladder on a level floor rather than a chair, have somebody foot it, and clear the floor under the unit before you start. If the window is above a stairwell, over a bath, or higher than a stepladder reaches, stop there and photograph what you can from below with the camera zoomed in. A unit out of reach is exactly the case where the photographs get taken during the survey instead.
On a centre pivot the plate is on the top edge of the sash, which faces the outside when the window is shut. To see it, open the sash, rotate it through 180 degrees so the outer face comes into the room, and engage the barrel bolt at the top of the frame to lock it in that position. That bolt is there precisely for cleaning, and once it is engaged the sash is held and both hands are free. The strip now facing you carries the plate. On a top hung unit the plate is usually on the sash top rail and is reachable with the unit propped open. Where a blind or a fly screen is fitted in the frame groove it will need unclipping first.
Reading it, and which parts of it matter
A plate carries more than most people expect and four items on it do the work. The product code, typically three letters, tells you the frame material and the way the window opens. The size code, usually a letter and two digits on a modern unit or three digits on an older one, fixes the frame dimensions and therefore the structural opening. The glazing code, commonly two digits, says what the sealed unit is. The manufacture date appears as a week and year or a plain year, and on a roof with several units it is the single most useful number there, because it tells you whether the others were glazed in the same week.
Photograph the whole plate rather than transcribing it. Codes are printed small, they contain characters that are easy to confuse by eye, and a photograph also captures the barcode and any serial reference. Turn the flash off and use the torch held to one side instead, because a direct flash on a glossy label produces a white square where the numbers were.
When the plate has been painted over or has gone
Four routes, in the order they are worth trying. First, look at the plate area under raking light with the torch held almost flat to the surface: a label under one coat of lacquer often still reads, and the embossed characters on some plates catch the light even when the print has faded. Do not attempt to abrade or strip it.
Second, look at the glass itself. Toughened panes carry a permanent kite mark etched into one corner with the standard reference and frequently a date, and it is visible from inside against a dark background. Third, look at the spacer bar inside the sealed unit through the glass at the edge, which sometimes carries a batch stamp or a manufacturer’s name. Fourth, look at the frame itself: some makers stamp or route a code into the top of the frame head behind the sash, and a few brand their hinges and their handles. Failing all four, the unit is identified by measurement, which is the next section.
Telling the four makes apart by what you can see
Where no code survives, the brand can usually still be established from the hardware and the profile. This is not exact and the survey confirms it, but it narrows the field enough to start.
| What to look at | What it commonly indicates |
|---|---|
| Handle in a continuous bar across the top of the sash, doubling as the ventilation flap control | The long-established centre pivot arrangement used on VELUX units, and copied in part by others |
| Handle at the bottom of the sash, top hung action | A top hung unit, or a centre pivot from a maker who places the handle low. Note which way it swings before ordering |
| Two-position or four-position locking catch with detents | Common on Fakro units, which have long marketed multi-position opening |
| Integral thermal break collar visible around the frame at the reveal line | A Keylite feature, supplied as part of the frame rather than as an accessory |
| Sash that both pivots and top hangs from a single mechanism | Roto, whose combination hardware is its distinguishing feature |
| External cladding in grey or brown pressed aluminium with a visible cover cap at each corner | Generation rather than make. Corner caps and their shape changed across decades |
| Clear lacquered pine gone honey-gold, no white anywhere | A timber sash from before white polyurethane became the volume product, so 1980s or 1990s |
| White frame with a slightly soft, seamed corner rather than a mitred timber joint | Polyurethane over a core, which places it from the late 1990s onwards |
Measuring, and the three dimensions worth writing down
Measurement is the fallback and it is more reliable than people expect if you record the right things. Take all three of these with a tape and note which is which, because quoting one when somebody assumes another is the commonest source of a wrong order.
- The sash outer size, measured across the moving part at its widest and longest, taken from inside with the sash closed.
- The frame outer size, measured across the fixed frame where it meets the covering, which is the dimension a size code refers to.
- The clear plastered reveal, measured at the head, the middle and the cill, because it is the only one a homeowner can always reach and it gives a working figure.
Record the structural opening if the loft side is accessible, measured between the trimmers and the rafter cheeks, and take the diagonals too. Bear in mind that the structural opening is larger than the frame by roughly 40 to 45mm on most modern ranges, so the two numbers are not meant to agree. Sizes and how they are coded are set out at roof window sizes and how they are coded.
Flat roof units, which mostly never had a plate
An acrylic or polycarbonate dome on a site-built kerb over a Gloucester rear addition, a Longlevens garage or a Tewkesbury bathroom extension will usually carry nothing at all. Occasionally there is a moulded maker’s mark in the underside of the flange at one corner, and occasionally an installer wrote a size in pencil on the inside of the kerb, but neither is common.
So a flat roof unit is identified by measurement and by material. Measure the aperture in the ceiling, then measure the kerb externally if you can reach the roof safely, and note the profile: a single-skin clear dome, a twin-wall or triple-wall dome with visible flutes, or a flat glazed unit. Note the colour, because bronze and opal domes were sold alongside clear ones. Then check the dimensions against the imperial sizes those units were built to, because 610 by 915 and 915 by 1220mm read as awkward numbers until you recognise them as 2 foot by 3 foot and 3 foot by 4 foot. Where the roof cannot be reached safely, it waits for the survey. What replacing one involves is at can you replace a rooflight on a flat roof.
Dating the unit from the house rather than the window
Where nothing on the unit survives, the building will often date it within a few years. A rooflight that went in with the original build dates to the house, and on the trussed estates at Quedgeley, Abbeydale, Brockworth, Innsworth, Ashchurch and Yate that places it firmly in the eighties or nineties. A rooflight in a loft room with a fixed staircase and a plastered ceiling dates to whenever the conversion happened, which the household usually knows. A rooflight in a rear addition kitchen with a flat roof over it dates to the extension.
Two documentary routes help as well. A Building Control completion certificate or a planning decision for a loft conversion will be in the deeds pack or on the local authority’s public register, and it gives a date and often a specification. And the previous owner’s paperwork, handed over at sale, sometimes contains the manufacturer’s warranty for the glass with the codes printed on it. Worth ten minutes in a filing box before anybody climbs a ladder.
The photographs that let somebody identify it for you
Five images make a first reply genuinely useful rather than a request for more information. The plate, close and legible, rotated into view if it is a centre pivot. The unit from inside the room, showing the frame, the sightline and the reveal around it. The unit from outside, from the garden or across the street, far enough back to show the covering and the run of slope. The top corners of the reveal, because that is where a cold bridge shows and it says something about how the original was insulated. And a wider shot of the roof so the access can be looked at honestly.
Add the address, roughly when you think the unit went in, and what has actually happened: cloudiness between the panes, water during rain from one direction, a mechanism that has stopped working, or a mark in the plaster. Send it to info@severnskylightsgloucester.co.uk. From that set the make, the size code and a current equivalent can usually be named by return, along with an indicative range, and only then is a survey worth anybody’s afternoon. Whether the unit you have can be matched is at can you match my existing rooflight, and the general approach is on the skylight and rooflight installation page.
Next on this subject.
- Question Do rooflights need planning permission? Usually not. Putting a rooflight into the roof of a house is normally permitted development, which means the national rules…
- Question Do I need building regulations approval for a rooflight? Yes. Forming a new opening in a roof is notifiable work under the Building Regulations, and it is notifiable whether…
- Question Who notifies building control about a rooflight? In law the duty sits with the person having the work carried out, which means the homeowner, and in practice…
- Question How much does a rooflight cost? There is no single figure, and any site that publishes one is quoting for a job it has not seen.…