Do I Need Planning Permission for a Skylight?

Whether you need planning permission for a skylight comes down to Class C of Part 1, Schedule 2 in the General Permitted Development Order 2015. It covers "any other alteration to the roof of a dwellinghouse", and in practice that means roof windows, rooflights and sun tunnels on a house. Planners call this rooflight permitted development, and it works as a set of conditions. Meet them all and you do not need to apply.

There are three. First, the unit must not project more than 150mm beyond the plane of the original roof slope. Second, it cannot stand taller than the roof's own highest point. Third, a unit on the side-elevation slope must be obscure-glazed, and any part of it that opens has to be higher than 1.7m measured up from the floor of that room.

The first two conditions are why the ordinary pitched-roof job is straightforward. On a pitched roof the window lies in the slope, near the tiles or slate, and its flashing lifts it only slightly clear of them. A sun tunnel dome on a pitched roof is much the same. Neither comes near the ridge.

• Projects 150mm or less from the roof plane
• Stays below the roof's highest point
• Side-facing slopes: obscure glass
• Side-facing slopes: no opening part below 1.7m

The third condition catches more people than the other two, and it is mostly a question of which slope you mean. A slope forms a side elevation when it faces the side of the house rather than the front or the back. Take a hipped 1930s semi in Crosby or Wallasey: the sloping end of the roof counts as a side-facing slope. A gable-fronted terrace or villa has side slopes running along the party wall side.

A window in one of those slopes has to be obscure-glazed whatever height it sits at. Opening is a separate rule. Any part of the window that opens has to be over 1.7m from the floor of the room. The measure is taken from the floor of the room itself, not the ground outside, which is why a roof window set high in a loft room can be allowed to open while the same window set low must be fixed. If you are unsure which of your slopes counts as a side elevation, show us the house at the survey and we will say.

Three situations take the right away or change the answer.

Flats and maisonettes. Permitted development rights under Part 1 are for houses. A flat or maisonette does not have them, so a new rooflight in the roof above you usually needs a planning application, and the freeholder's permission as well. If you own a top-floor flat in a converted Victorian house, start with the planning authority.

Listed buildings. Listed building consent is needed for alterations that affect the character of the building, and a new or replacement rooflight usually does. That is a separate system from planning permission, and permitted development does not remove it. The detail is in listed building consent for a rooflight.

Article 4 directions. Where a council makes an Article 4 direction, permitted development rights are withdrawn across a defined area, and conservation areas are a common choice for one. Where one applies, a rooflight that would otherwise be allowed needs a planning application. Conservation area status alone does not take away the Class C rights, but a direction in the area can. The conservation rooflight hub explains how to check.

Class C is written around a unit that sits close to the roof. A roof lantern stands up from a flat roof, usually well beyond 150mm, so it does not sit comfortably inside that condition. How a lantern on an extension is treated depends on the extension and on the council, which is the one case where we suggest asking before ordering. For a lawful development certificate, which is the council's written confirmation that your plan is lawful, the Planning Portal sets out how to apply. It is worth having if you plan to sell. Flat roof rooflights, which sit on a low kerb, are a closer call and the same advice applies.

The front of the house gets its own question, because people worry about what the street sees. That question has its own answer: a roof window on the front slope and planning.

Everything above describes England. Wales makes its own permitted development rules, and they are not word for word the same. In Flintshire County Council's area or Wrexham County Borough Council's, the Welsh permitted development rules replace these. Check the current position on gov.wales or with the planning team at Flintshire or Wrexham. Listed buildings in Wales are handled through Cadw.

Planning is one half of the paperwork. The other half is the Building Regulations, which apply to rooflights whatever the planning position, and which we cover separately in rooflights and Building Regulations. Notification to Building Control is something we take on when the work calls for it. To have a surveyor look at your roof and tell you which rules apply, get a free quote. You get the survey first, then one fixed quote on paper.