What makes a rooflight a conservation rooflight?

There is no regulation that says what a conservation rooflight must be, so the term describes a family of products with shared features. These are the ones you will see on most:

Slim frame

The metal frame is narrow, often steel or aluminium finished to look like steel, so the glass takes up most of the visible area and the frame reads as a fine line.

Flush profile

The unit sits low on the roof slope, usually only a short way above the slates or tiles, rather than standing up on a deep kerb. That keeps the silhouette clean from the street and keeps it within the 150mm projection limit under permitted development.

Glazing bar

Many have one or more bars across the glass, in the manner of old patent glazing. A bar is a feature of the traditional look and not a necessity, and some makers offer a bar-free version, a subject covered in our answer on glazing bars.

Traditional finish

The frame is normally painted in a dark, matt colour such as black or a deep grey, and the flashing is dressed to match the roof covering. A bright white frame or visible plastic is not part of the look.

Steel gives the thinnest section and the most authentic character, and it needs a decent coating to resist rust in a damp, coastal county like Devon. Aluminium can be made slimmer than it first appears and is lighter, with a longer-lived finish. Each has its supporters, and the choice depends on the building and your budget. Our guide to steel or aluminium conservation rooflights sets out the differences.

Modern units are not the thin, single-glazed castings of the nineteenth century. Underneath the traditional outline, most use a sealed double-glazed unit with a low-emissivity coating and a warm-edge spacer, so they meet current thermal standards. Looking old and performing like a new window are not in conflict.

A conservation rooflight is not simply any rooflight on a conservation area roof. A standard roof window with a thick white frame and a deep flashing can be fitted in a conservation area, if the planning rules allow, but it is not a conservation rooflight. Likewise, a plastic dome on a flat roof has little in common with one.

It is also not a guarantee of consent. Using a conservation-style product helps an application on a listed building or in a sensitive setting, but it does not replace listed building consent or an answer from the planning authority. Whether you need either is explained in our answer on planning permission.

The easiest way to see the difference is to put the two side by side on the same roof. A standard roof window usually has a wider frame in white-painted pine or polyurethane, a deeper flashing and a pivot or top-hung sash that opens. A conservation rooflight has a thinner metal frame, sits closer to the roof surface, and in most versions is fixed, though opening versions with a hinged sash exist.

• The frame is a fine dark line rather than a broad pale surround.
• The glass runs close to the slates, so there is little visible upstand.
• The flashing is dressed neatly to the roof covering, not stood off it in a deep tray.
• A bar, where fitted, breaks up the glass in the way old patent glazing did.

None of this makes a roof window wrong. A standard window with a good flashing kit is the right choice for many loft rooms, and it opens easily for ventilation. A conservation rooflight is the better choice when the look of the roof is the priority.

Most conservation rooflights are fairly small, which suits the scale of the originals and the rafter spacing of old roofs. They are often made to fit between rafters at traditional centres, which avoids cutting timbers in a roof you want to disturb as little as possible. Our answer on what size suits a cottage goes into this.

If you want ventilation, ask whether an opening version is available in the size you want, and how it opens. Many fixed units are sold for light alone, and in a bathroom or kitchen under an old roof you may want a separate way to clear steam. Opening rooflights can contribute to purge ventilation, but the size of the opening and its position in the room decide how well they do it.

They suit slate and clay-tile roofs on period buildings: Georgian and Victorian terraces in Exeter, cob and stone cottages in the Exe and Culm valleys, converted farm buildings and the older streets of the coastal towns. They are also used on newer houses where the owner simply prefers the fine-framed look. On a pitched roof of natural slate, a flush frame is particularly effective, and our guide to conservation rooflights on slate roofs explains how the flashing is handled.

A traditional-looking frame on the roof is only half of the picture. In an old house you also see the opening from the room, and a plain plasterboard box with a modern trim can undo the effect. Lath and plaster or lime-plastered ceilings need an opening cut with care, and the lining is often best splayed so it echoes the reveals of the windows. We record the lining shape and finish in a finish schedule that comes with every quote.

The conservation rooflights page covers the range in more detail, and you can ask for a quote once you know the roof.