Fitting a skylight, or a roof window as the trade calls it, changes the outside of a house, so people reasonably ask whether it needs planning permission. For most houses the answer is no, because the permitted development rules allow it within limits. For some buildings the answer is different, and the difference depends on what the building is, not on the window.
The permission question has four parts. First, is it a house, a flat or a listed building? Second, does the window stay within the projection limit that Class C sets? Third, if it sits on a side slope, does it meet the glazing condition? Fourth, is there a conservation area, a National Landscape or an Article 4 direction that withdraws rights?
Planning permission is separate from Building Regulations. A skylight that needs no planning permission still has to meet the Regulations on insulation, structure and escape, so we cover both. The information is general and not legal advice, so check your address with the planning team of your council. For addresses in Rushmoor that is Rushmoor Borough Council, and for Fleet and the Hart villages it is Hart District Council.
Class C and the 0.15 metre limit
Houses get their permitted development rights from Schedule 2 Part 1 of the General Permitted Development Order 2015. Class C of that schedule is the catch-all for roof alterations on a house, and a skylight is exactly that.
The projection limit
Under Class C an alteration is ruled out if it would stand more than 0.15 metres proud of the original roof surface, measured at right angles to that surface. That is about six inches. A roof window lies in the plane of the roof and rises only by the depth of its frame and flashing, so it normally passes this test easily.
Where the limit bites
A window that stands up from the slope, such as a domed rooflight on a raised kerb or a roof lantern, may go beyond 0.15 metres. Those need a closer look, and some will need planning permission. A rooflight on a flat roof sits on its own upstand, so the measurement is taken from the roof it stands on.
Like-for-like replacement
Section 55(2)(a) of the 1990 planning Act leaves out of "development" any work that leaves the outside appearance of a building materially unchanged. Swapping an old skylight for one of identical size and look therefore usually falls outside planning control. A change of size or position is a different matter.
What this class leaves out
Class C is a right belonging to houses. Flats, listed buildings and conservation areas are treated below, and each has its own consequence.
The side-slope glazing condition
Class C carries one condition that catches homeowners out. It applies to any window put into a roof slope that makes up a side elevation of the house.
What it requires
Condition C.2 sets two requirements. Such a window has to be obscure-glazed. It also has to be non-opening, except that the parts which open may do so when they are over 1.7 metres up from the floor of the room.
Reading the two parts
They work differently. The obscure glazing requirement is unconditional, so a side-slope window is obscure-glazed whatever its height. The 1.7 metre figure belongs only to the opening requirement. A window whose opening parts sit above that height may open, while one whose opening parts are lower must be fixed shut.
A common slip
The rule is sometimes summarised in a way that suggests height removes the need for obscure glass. It never does, and a roofer who tells you otherwise is giving you half the rule.
Why the rule exists
A window in a side slope can look sideways into a neighbour's garden or bedroom, and the condition is there to protect that privacy. That is why it is the glazing that is fixed by rule, and why the opening restriction eases once the sill is high enough that nobody can look out of it.
Which slope counts as a side
On a gable-ended house the side slopes are the long faces, while on a hipped house the plan needs a closer look. If you are unsure whether a slope counts as a side elevation, ask the planning team to confirm. Our answer on a roof window on a side roof slope goes through it with examples.
Flats, listed buildings and protected landscapes
Class C is a right that belongs to houses. The type of building, and the land it stands on, change what you can do.
Flats
Under the Order, a dwellinghouse is not a block containing flats, nor a flat within one. Flats therefore have no permitted development rights, and Rushmoor makes the same point in its conservation guidance: works to flats need permission unless they replace like with like and leave the appearance alone. A new skylight in a top-floor flat normally needs an application.
Listed buildings
A listed house keeps its Class B and Class C rights, because the Order has no listed-building exclusion. It also needs listed building consent, under section 7 of the 1990 Listed Buildings Act, wherever the work touches its character. A new hole in an old roof is likely to do so. Our answer on a roof window in a listed building sets out the route.
National Landscapes and National Parks
Article 2(3) land takes in conservation areas, areas of outstanding natural beauty and National Parks. Class C has no exclusion for that land, so it does not bar a roof window. The restriction bites on dormers, which Class B refuses on article 2(3) land.
Dormers
A dormer is a different thing from a skylight. Class B caps its volume at 40 cubic metres on a terraced house and 50 elsewhere, and rules it out on a slope that is the principal elevation facing a highway.
Conservation areas and local directions
Class C has no conservation area exclusion, so a skylight on a house in a conservation area is usually still permitted development. A local direction can change that, so the next step is to find out whether one covers your address.
How directions work
Under article 4 of the Order, national or local planning authorities may take named permitted development rights away across a defined area. Each council makes its own, and what each one covers differs from place to place.
Rushmoor
Rushmoor has nine designated conservation areas. In Farnborough itself they include Farnborough Street and South Farnborough. Its directions in force include Cargate in Aldershot, where works seen from the street or open land are controlled, and Wellesley, which deals with front hard surfaces, gates and walls and antennas facing a road. The council's planning team can tell you whether any applies to your house.
Hart
Hart District Council made directions in 1998 for most of its conservation areas. Their wording covers altering the frontage of a dwelling, and it names the frontage roof slope. A roof window facing the street in one of those areas could therefore need an application. Hart gives no single count of its conservation areas, so use its map to check.
Elsewhere
Other councils have their own lists. Our answer on a roof window in a conservation area sets out how to check.
Building Regulations still apply
Planning permission is about appearance and land use. Building Regulations are about how the work performs, and they apply to a skylight whether or not planning permission is needed.
Insulation
A skylight is a hole in an insulated roof, so its performance matters for the room below. Approved Document L, the 2021 edition with the 2023 amendments, gives figures for new elements in an existing house. A window, roof windows included, should reach 1.4 W/(m²·K) or at least Window Energy Rating Band B. A rooflight has its own figure of 2.2. A skylight in a pitched roof is normally a roof window and takes the window figure. Roof windows are not thermal elements, so fitting one is not a renovation of the roof.
Structure
A new roof window usually means cutting into rafters and trimming an opening, which is structural work, so we ask the building control body whether an application is needed. For Rushmoor and Hart addresses, call the Hart and Rushmoor Building Control Partnership on 01252 398715.
Escape
In a loft room, the roof window may serve as the escape window. Approved Document B asks for a clear opening of at least 0.33 square metres, at least 450 mm high and wide, with the bottom of the opening no more than 1100 mm above the floor. Such windows count only for storeys within 4.5 m of the ground. Our answer on roof window Building Regulations goes into it.
A date to watch
The 2026 edition of Approved Document L takes effect on 24 March 2027, so check which edition governs your job.
Working out which route applies to you
You can settle most of the planning question by taking a few steps in order. It takes ten minutes and a look at your paperwork.
Step one: what is the building?
A flat, or a house converted into flats, has no permitted development rights, so an application is needed. A single house goes on to the next step.
Step two: is it listed?
Check the national list or ask the council. If it is, listed building consent is needed for anything touching its character, alongside any Building Regulations application.
Step three: where does it stand?
Ask the planning team whether the property is in a conservation area and whether a direction applies. For a house in one of Hart's directed areas, a window on the slope facing the street may need permission.
Step four: which slope, and how far does it stand proud?
A side-slope window must be obscure-glazed, without exception. Separately, it has to stay shut unless the opening parts are over 1.7 metres up. On any slope it must stay within 0.15 metres of the original roof plane.
Step five: the Regulations
Check the insulation figure and the structural opening and, if the window is an escape route, the Approved Document B sizes. File the council's reply and any building control letter safely, as a future buyer may want to see them.
With those answers in hand, a survey confirms the roof, the rafters and the position, and the written price follows. Our roof windows and skylights page covers the installations we carry out.
