A thin frame set close to the slope
Most roof windows stand a little proud of the roof. The frame is boxed, the glass sits in a raised sash, and the flashing (the sheet metal or moulded kit that carries water around the opening) steps up to meet it. A conservation rooflight turns that around. The frame is narrow, the glass lies close to the line of the slates or tiles, and the surround is detailed so the opening looks like a thin sheet laid into the roof.
The name comes from older roofs, where a heavy modern frame can look out of place beside hand-cut slate or clay. It is a description makers and roofers use, not a term defined in planning law. That matters later in this answer, because the rules look at the work you are doing, not at what the product is called.
When you compare products, ask the supplier for three plain figures: how far the frame stands above the roof covering, how wide the frame is on each side, and which metal the flashing is made from. Those answers tell you how flush the unit really is, and they are the numbers a council officer will ask for.
Why a flush unit helps under Class C
For a house that is not a flat, a new roof window normally falls under Class C of the General Permitted Development Order, the class that covers alterations to a dwellinghouse's roof. A slim, flush rooflight suits it well, because one of its limits is about how far a fitting rises from the roof. Class C falls away when a fitting would rise more than 0.15 metres above the original slope.
Three more points matter for any rooflight:
- The new fitting cannot become the tallest point of the roof.
- Class C does not cover altering a chimney or flue, or soil and vent pipework.
- A window in a side slope has its own glazing condition.
Flats and maisonettes have no permitted development rights at all, so a flat needs an application whatever the rooflight looks like. The full set of Class C tests, including the side-slope wording, is in our roof window planning guide. Measure the projection from the supplier's drawing, not from a brochure photograph, and measure from the original roof surface.
Conservation areas and an Article 4 check
The style is made with period roofs in mind, including those in a conservation area. Being in one does not remove Class C: conservation areas count as article 2(3) land, which takes away Class B (dormers) but not Class C. An Article 4 direction can still change the answer, because it lets a council withdraw specified permitted development rights across a defined area.
Councils publish this differently. Thanet lists 27 conservation areas, and its Article 4 directions apply in three conservation areas, namely Pegwell, Ramsgate and the Marina extension at Ramsgate. Canterbury says its district has 97 conservation areas, Dover 57 and Swale 51. Dover adds that its directions can touch roof alterations on dwelling parts that look out onto roads, waterways or public open space.
Nobody can tell you from a postcode alone whether a direction covers your roof. Ask your council whether an Article 4 direction applies, and say which slope the rooflight would be on. Folkestone and Hythe publishes an interactive map instead of a count, so for a house there the map and a call to the council are the route.
Listed houses and what to put in front of the council
A listed house keeps Class B and Class C, but listed building consent is also required where the work changes the building's character, under section 7 of the Planning (Listed Buildings and Conservation Areas) Act 1990. A rooflight changes the roof, so assume consent is in play and ask first. Our answer on fitting a roof window on a listed building covers that route in more detail.
Whatever your house, a request to the council goes better with a short pack:
- The supplier's section drawing, showing frame width and projection.
- Which slope and which rafter bays the opening would use.
- The covering around it and how the flashing would be formed.
- A photo of the whole elevation, taken from the street.
A council may also ask about the glass: clear, tinted or with a coating, and whether the unit opens. Have the supplier's data sheet to hand when you ring. Allow time for a reply, since the officer may want to see the roof before answering. For the wider choice of products, see roof windows and skylights.
