What is a conservation rooflight?

Stand across the lane from a cottage with a conservation rooflight and the first thing to notice is how little there is to notice. The pane lies a few centimetres above the peg tiles, the frame is a thin line in black or charcoal, and the single bar splits the glass into two tall halves. A standard rooflight often shows as a pale rectangle on a raised kerb.

The difference comes from construction. A conservation unit has a shallow upstand or none, and the flashing is formed to the profile of the tiles around it. Slim sections of aluminium or steel-look metal hold the glass on a narrow bar, so the frame takes up little of the view from inside as well. We carry section samples to the survey and hold them against a tile from your own roof.

Approved Document L has its own definitions. A rooflight is a glazed unit set out of plane with the roof on a kerb or upstand, while a roof window sits in the same orientation as the surrounding roof and in plane with it. A conservation unit can fall into either, depending on the build, and the answer matters because the energy limit differs: 2.2 W/m²K for a rooflight, 1.4 W/m²K (or Window Energy Rating band B) for a roof window under Table 4.2 for existing dwellings. We confirm which family the chosen unit belongs to when we specify it.

Roof window makers, VELUX among them, sell heritage-style models next to units made by specialist fabricators for conservation work. We install and replace both. The pitch, the depth of the rafters and the look you want from the lane decide which suits. Our page on minimum pitch for a roof window shows why a shallow slope narrows the choice.

A slim frame helps with a conservation officer or a planning officer, but nothing in the name overrides the rules. Class C permitted development applies to a house roof only within its conditions, among them that the unit sticks out no more than 150 mm, frame included, beyond the plane of the original roof slope. A low profile helps meet that. Being in a conservation area does not remove Class C by itself; only an Article 4 direction does, and our guide to conservation area rooflight planning explains how to find out.

For a listed house, a new or altered roof window will almost always need listed building consent. Read rooflights on listed buildings before drawing anything. The position for your address is checked on the survey visit.

The units suit rooms inside old roofs where the covering must stay as it is: a first-floor bathroom squeezed under a slope, a sloping-ceilinged box room, a dressing room at the head of a stair, or a scullery in a lean-to behind a ragstone cottage. Each has little wall to put a window in, and a pane in the slope sends light into the middle of the floor.

For a house with clay tiles, our guide to a conservation rooflight on peg tiles covers the fit. If the dark room sits under a flat-roofed extension behind an old house, a lantern or flat rooflight may suit better, and our flat roof rooflights pages cover those. A roof lantern on a flat roof usually stands more than 150 mm proud, so it normally needs planning permission unless the council confirms otherwise.

Our full range of heritage work is set out on the conservation rooflights page. If you want a unit measured, book a free survey; the fixed written quote that follows names the frame, the glass and the Building Control notification, and the work carries a 10-year workmanship guarantee in writing.