What is a conservation rooflight?

Three defining features

It sits flush. Nearly level with the tiles or slates rather than proud of them, so from the street it reads as part of the roof. It also comfortably clears the 150mm permitted development allowance.

One central bar. A single vertical glazing bar, echoing the original two-pane cast iron units. Not a grid, which reads as a window; not none, which reads as modern.

A slim black frame. Powder coated steel or a steel and timber composite, with a much narrower sightline than a domestic roof window.

Modern performance

Double glazed with a low emissivity coating, comfortably meeting current requirements. The appearance is historic; the specification is not. Nobody is asking you to accept single glazing for the look.

Why they cost more

Steel rather than timber or plastic, slim sections doing the same structural job with less material, and a flush detail that takes considerably longer to fit, particularly into pantile.

Where they are used

Conservation areas, listed buildings, and any period property where a standard roof window would look wrong. In Colchester that is a large share of the borough. Detail on the conservation page.

A rooflight designed to look historic

A conservation rooflight is a steel framed, low profile unit designed to sit close to the plane of the roof covering, upright in proportion, with a central glazing bar and a matt black finish. It exists because conservation officers and listed building consent regimes will not accept a standard modern roof window on a historic roof.

It imitates the cast iron rooflights that were fitted to English roofs from the nineteenth century onward, which were tall, narrow, divided by a vertical bar and set almost flush with the slates.

The four characteristics that matter

It sits low. More important than everything else combined. From the ground, the roof reads as a roof with a dark rectangle in it rather than a roof with a box on it. This is what the manufacturer’s section drawing shows, and it is the question a conservation officer actually needs answered.

It is upright. Taller than it is wide, because that is what the original cast iron sizes were. A wide landscape unit reads as modern immediately, however correct everything else about it is.

It has a central glazing bar. The vertical bar dividing the glass is the visual signature of a historic rooflight, and its absence is the single most common reason a design is refused.

It is matt black or very dark. Not gloss, and not white or light grey, which read as plastic at any distance against a clay or slate roof.

What you give up

Accessories. Mass market roof windows have a whole ecosystem of clip in blinds. Steel conservation units generally do not, so blinds become a separate made to measure item fitted to the reveal. Budget for it at the start.

Cleaning. Most conservation units are top hung or side hung on a stay rather than centre pivot, so the outer face cannot be turned inward. On anything above easy reach, decide how the glass gets cleaned before it goes in.

Size range. Traditional proportions rather than the full modern range, and outside that you are into made to measure with several weeks of lead time.

The view. The glazing bar divides it and casts a line across the room. That takes getting used to, and it is the reason the roof looks right from the street.

What you do not give up

Thermal performance. A modern conservation unit is properly double glazed with a warm edge spacer and clears Part L comfortably. There is no performance penalty for choosing one.

The exception is a genuine surviving Victorian rooflight retained for heritage reasons, which is a single glazed hole in the roof. Where one is being kept, secondary glazing below it is usually the compromise a conservation officer will accept.

When you actually need one

On a listed building, almost always, because consent is required and this is the design that gets approved. In a conservation area with an Article 4 direction, usually. On a rear slope screened from every public vantage point, sometimes not, and it is worth asking rather than assuming the more expensive product is compulsory.

Where a standard unit would be consented, we will say so.