Answered · Skylight & Rooflight Installation & Replacement Chelmsford

Can you match my existing rooflight?

The short answer

Usually, and the useful first step is working out which kind of matching you mean. Matching the size so nothing structural moves is nearly always achievable. Matching the external appearance so a pair reads as a pair is achievable most of the time. Matching a discontinued product exactly, unit for unit, is the one that sometimes has to be solved a different way.

Those three are different problems with different answers, and conflating them is why the question gets a vague reply. This page separates them out and says what is possible in each case. It forms part of the wider skylight replacement work Sunspire carries out across Chelmsford and the thirty miles of Essex around it.

Three different things people mean by matching

The first is dimensional. The opening exists, the trimmers are in, the plaster is finished, and the requirement is a unit that goes into that hole without anybody cutting timber. That is a measuring exercise.

The second is visual. There are two or three rooflights visible in one glance from the garden or from the room, one has failed, and the new one has to look like its neighbours. That is a specification exercise about frame colour, profile depth, glass tint and how far the unit stands proud.

The third is literal. Somebody wants the identical product because it is part of a scheme, or because a conservation officer approved that unit, or simply because they liked it. That is a sourcing exercise and it is the one with the most variables.

Matching the size so nothing structural moves

This is the one that matters most for cost and programme, and it is the easiest to get right. Roof window manufacturers have kept the external frame dimensions of their common sizes remarkably stable over decades, which means a current unit will very often drop into an opening trimmed in the nineteen eighties for the same nominal size.

Flat rooflights are less consistent, because they are sized against the internal kerb dimension and older kerbs were built to imperial numbers or to whatever the carpenter had. Where the catalogue sizes fall either side of the opening, the fix is to take the next size up and pack the kerb in, or to order made to measure to the actual dimension. Both work. The first is faster, the second avoids touching anything.

Matching the appearance from the garden

Stand where the rooflights are actually seen from and four things decide whether a new unit reads as a match.

Projection. How far the unit stands above the plane of the covering. Recessed and standard flashing options change this by twenty or thirty millimetres, which is visible on a slope.
External frame colour. Grey aluminium cladding is close to universal on modern roof windows and reads consistently against most coverings.
Glass tint. Solar control coatings carry a colour, usually a faint blue or bronze, and a coated unit beside an uncoated one is noticeable in flat light.
Frame proportion. Sightline widths differ between manufacturers and between generations of the same manufacturer.

Matching what you see from inside

The internal finish is a separate decision from the external one and it is often the one people actually care about, because it is in view every evening.

The mainstream options are a clear lacquered pine, a white painted timber, and a white polyurethane coated finish used in bathrooms and kitchens where humidity is high. A pine sash beside a white one in the same room is obvious. What is less obvious is that lacquered pine darkens with age, so a new pine unit alongside a twenty year old one will be noticeably lighter for the first several years before it catches up.

Where the old unit records its own size

Most units carry their own identity somewhere, and finding it removes the guesswork entirely. On a roof window the data plate is usually on the top rail of the sash, visible when the sash is rotated, and it carries the manufacturer, the model, a size code and a year of manufacture.

Flat rooflights and lanterns are less consistent and the label, where one survives, tends to be on the underside of the frame or inside the base. Where nothing is legible, the unit is identified by measurement and by its details instead, which is covered on our page about identifying an existing rooflight.

When the product has been discontinued

Ranges are updated, sizes are dropped, and finishes are retired. A unit fitted twenty five years ago will very often have no direct current equivalent, and that is the ordinary case rather than a difficulty.

There are three routes through it. A current unit from the same manufacturer in the nearest size, which is usually dimensionally compatible because the size grids have persisted. A unit from a different manufacturer that matches the dimensions and the appearance more closely than the original’s own successor does. Or a made to measure unit built to the exact opening, which costs more and takes longer and solves the problem completely.

Matching one of several on the same roof

Where a roof carries three units of one vintage and one has failed, matching the failed one is technically the question and rarely the right one. Units of the same age are on the same clock, so the two that look fine today are three or four winters from the same condition.

That is why the matching conversation so often turns into a conversation about doing the set. Our page on replacing several at once works through when that is worth it and when staging the work makes better sense. Where only one is being done, ordering the closest current equivalent and accepting a small difference in tint is entirely reasonable.

Conservation frames and matching a heritage look

In the protected fabric of Thaxted, Coggeshall, Saffron Walden and the older cores of the market towns, matching means something more specific. A conservation rooflight is characterised by a slim black or dark grey cast or steel frame, a central vertical glazing bar, and a unit that sits flush or nearly flush with the plane of the slates.

Those characteristics are what a conservation officer is looking at, rather than the brand on the label, and several manufacturers make units that satisfy them. Matching an existing approved rooflight on the same elevation is therefore a matter of matching the module, the bar position and the projection. Our conservation rooflight page covers what those frames actually are.

What the survey settles about a match

Four measurements and two photographs resolve almost every version of this question. The external frame size or the internal kerb size, the depth of the frame, the projection above the covering, and the position of any glazing bar. Then a photograph of the data plate if one survives, and one of the unit in place from the angle it is normally seen from.

Sent by email, that is usually enough for a range and a shortlist of two or three candidate units. The survey then confirms the opening is what the tape said it was, which on a roof of any age is worth doing before an order is placed rather than after.

Tell us about your roof

We start with the building, the covering and the slope. Then we tell you what will suit it, and what it will cost, as a fixed written number.

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