How much does a conservation rooflight cost?

Width and length set how much frame and glass go into the unit, and how large an opening has to be cut. A run of two or three units along a long slope changes the job, with more flashing and more trimming of the rafters. A wide unit can mean more work to the rafters either side, which belongs with the structure described below. Conservation units are chosen or made to suit the opening, so the room and the opening decide the size, not the nearest stock size.

The slim frame is where the type earns its name, and it is also where makers differ. Steel is the traditional choice at some makers, while others build in aluminium, available in a wider range of colours. A bespoke colour or a finish matched to existing metalwork can change the figure compared with a maker's standard range. Where a centre glazing bar is wanted, it is part of the frame design and can change the figure, as can a two-colour finish, where a maker offers one.

Some makers start from double glazing. Triple glazing, which some makers offer, makes the pane thicker and changes the figure, and a coating that cuts the sun's warmth is offered on certain models only. A flush unit in a pitched roof is a roof window under Approved Document L. In England, a new or replacement roof window in an existing home should have a U-value no worse than 1.4 W/m²K, or a Window Energy Rating of Band B or better. Compare units on each maker's datasheet figure.

The flashing, which seals the unit to the covering, is made for that covering. Natural slate, plain tile, profiled tile and stone slate each need their own detail, and the more irregular the covering, the more individual fitting it takes. Slates that have gone brittle can crack when lifted for relaying, so the survey checks for it before the figure is set.

The opening usually has to be cut, trimmed and supported, and how much of that is needed depends on how big the unit is and how the rafters run. Reaching the roof is another variable: a tall house or a narrow side passage can mean scaffolding or other access equipment. Inside, the lined opening between the roof and the room is insulated, boarded and plastered. Check whether the work stops at plaster or includes decorating before you compare two figures.

A fixed unit is the simplest option. Where a model includes a vent, whether pole or motor, that changes the figure. A motor needs wiring to a switch or a remote, and that is simplest to arrange before the ceiling lining is finished. On certain electric vents, some makers fit a rain sensor as an option. A blind is made for the unit's size and maker, and some makers offer blackout, pleated and damp-room styles. Deciding these early is easier than wishing for them later.

In England, adding a rooflight or roof window to a house is usually permitted development under Class C, so it does not need a planning application, provided it meets the Class C limits and conditions. Conservation units face the same tests, set out in the skylight planning permission guide. If the right has gone at your address, through an Article 4 direction or an old condition, a planning application comes first. Class C has no listed-building exclusion in England, so a listed house still has Class C planning rights, but a new or altered rooflight on a listed building will almost always need listed building consent, and that consent decides the job. Applying for listed building consent carries no fee. Where the work is notifiable, we handle the Building Regulations notification with the council's building control team or a registered building control approver. Conservation areas and listed houses, and which route fits which house, are covered in the conservation area and listing guide.

A photograph shows the outline of the roof; the rafters, the covering and the access need to be seen in person. No number is set before the free survey. For a head start, WhatsApp 07880 284133 takes photos of the covering and the room. The quote itself is a fixed written quote. Once the conservation unit and its flashing are in, they sit within a written 10-year workmanship guarantee. For other kinds of unit, the costs page gives the wider picture.