For many houses, fitting a roof window needs no planning application. The rules class it as a roof alteration, and a national permission covers it while the unit stays close to the slope and below the top of the existing roof. That permission has conditions attached, and a handful of streets in Worthing and Shoreham have had it withdrawn, so the answer depends on the building in front of you rather than on the window.
Three checks settle nearly every case. First, is the property a house or a flat, because flats do not get the same rights. Second, does it sit in a conservation area or the South Downs National Park, or is it listed, because extra controls then apply. Third, which way does the slope face, because a window on a side slope carries a glazing condition that catches many people out.
This guide covers the national rule, the side-slope condition, the local directions that remove it, flats, listed buildings and the point where a roof window turns into a dormer. Planning is separate from Building Regulations, which have their own page: Building Regulations for roof windows. The wider range of work we do on this subject sits under skylights and roof windows.
The permission that covers most roof windows
Planning law lists what a householder may do to a house without applying, and Class C of Part 1 in the General Permitted Development Order is the entry for roof alterations. A roof window, a skylight set in the slope or a rooflight all fall under it, provided they stay inside three limits.
The first limit is projection. The unit may not stand more than 0.15 metres proud of the slope as the original roof was built, measured square to the outer face of that roof. The second is height: no part may be taller than the top of the original roof, so a unit close to the ridge cannot poke up past it. The third is scope. Class C does not stretch to chimneys, flues or soil and vent pipes, nor to solar panels, which are dealt with under their own heading.
Why 0.15 metres matters on site
A roof window is built to sit flush with the surrounding covering, and its flashing frame adds some thickness. On a roof laid with deep profile tiles the margin can be thin. Before ordering, we measure how far the finished unit will stand off the covering, check that against the limit and give you the figure alongside the quote.
A glazed unit on a raised kerb is a different product, a rooflight, and it stands further out. On a pitched roof that can push it beyond 0.15 metres, which is one reason to know the two apart. Our guide on the difference between a rooflight and a roof window sets out how each is defined.
The permission belongs to dwellinghouses. A block of flats, or a shop with a flat above it, needs a separate look, which comes later in this guide.
Side slopes and the obscure glazing condition
Class C carries a condition that causes most of the trouble. A window in a slope that forms a side elevation of the house has to be obscure-glazed. It also has to stay closed, except where the openable parts are over 1.7 metres up from the floor of that room.
The two halves are easy to blur, so read them apart. Obscure glass is needed for every side-slope window, whatever its height. The 1.7 metre figure governs only the opening rule. A window whose openable part sits at 2 metres may open, and it must still be obscure. One lower than 1.7 metres has to be obscure and fixed.
Which slopes count as side elevations
On a simple gabled house the long front and rear slopes face the street and garden, and the sides are walls, so there is no side slope. A hipped roof has four faces, and the two short ends look sideways. Hipped bungalows are common on this coast, and their end slopes are easy to overlook. A semi-detached house with a cross gable can have a side-facing slope too. If you are unsure, send a photograph of the house from the road and we will say which slopes are side elevations.
A clear roof window on the end slope of a hipped bungalow is a frequent reason for needing an application after the fact. Obscure glass still lets daylight in, which is the point of the window.
Many ranges offer an obscured pane as an option at order. How that works is covered in obscure glass in side-slope roof windows.
Conservation areas, the National Park and listed buildings
People often assume that a conservation area means every roof change needs consent. The national rules say otherwise. Class C has no carve-out for conservation areas or National Parks, so a roof window can remain permitted development in either, unless a local direction or a condition has taken the right away, or the building is listed. The postcode alone never answers the question.
The South Downs National Park matters because part of the Worthing area lies inside it. Across the recovered areas, which include Adur and Worthing, Arun, Horsham and Brighton and Hove, the Authority, not the council, decides planning matters. In Worthing, Castle Goring and Highdown are the conservation areas that fall to the Authority for planning. Class C survives Park location by itself, but the Authority takes your questions.
Listed buildings are different
A listed building needs listed building consent for work that changes its special character, and proceeding without it is an offence. Permitted development does not override that. Opening up a listed roof for a new window will usually count, and enforcement against unauthorised listed work has no four-year cut-off.
On a listed or very old roof, a slim unit that lies flush with the covering is the usual starting point. Our page on conservation rooflights covers the design.
Dormers are in another position
A dormer comes under the roof addition class, which has no application on land designated as a conservation area or National Park, so a dormer there goes through a full application. The comparison is set out in roof window or dormer.
Where a local Article 4 direction takes the right away
An Article 4 direction is how a council withdraws chosen permitted development rights from a mapped area. Adur and Worthing Councils stress that it does not ban the work: planning permission is simply required for what the direction lists. For roof windows, the directions we have read matter in five places.
- Old Shoreham conservation area. In force from 20 January 2023. For houses that face a public road or path it removes Class C, which the notice words as alterations to the roof, with coverings, rooflights and solar panels named. Chimney, flue and soil pipe changes are removed anywhere.
- Kingston Buci conservation area. In force from 10 February 2023, with the same shape: Class C for front-facing roofs, and the chimney class.
- Warwick Gardens, Worthing. Made in 2001. Where the house faces a highway or open space, changing how a roof slope is shaped or what it is made of needs permission, as does any chimney change.
- Warwick Place, Worthing. Made in 1997. Where the house faces Warwick Place, Class C roof alterations need permission.
- Western Row, Worthing. Made in 1978 and noted as removing dwellinghouse rights, including altering a dwellinghouse.
Two practical points follow. Where a direction covers only front-facing roofs, the rear slope is untouched, so a window at the back may be fine while the same unit facing the street needs an application. Other directions may also exist, so for any conservation-area house the safe step is a written question to the planning team.
The two councils share a planning team at Worthing Town Hall but remain separate planning authorities with their own directions. Their list is on the Article 4 directions page.
Flats, maisonettes and converted houses
The Part 1 rights belong to dwellinghouses, and the Order spells out what that word leaves out: a building containing one or more flats, and a flat within such a building. So a roof window in a flat, or in a house split into flats, does not have the Class C permission.
That does not mean refusal. It means applying in the usual way, and councils often grant a modest roof window where it suits the building. It does mean the house rules, 0.15 metres included, are no safe harbour.
Check how the property is classed
We meet this in top-floor flats, converted seafront villas and large houses divided into maisonettes. In each, the first question is how the property is classed, not how big the window is. A house converted to flats long ago may have lost its house rights though it still looks like a house from the road. If the title is unclear, the planning team can say how the council treats the building.
A flat brings in others besides the planning authority. A leaseholder normally needs the freeholder's agreement before cutting into the roof, which is often part of the structure the freeholder maintains. Raise it with the managing agent early, since both answers are needed and can arrive in either order.
The legislation also lists amendments to the definitions that were not yet applied when we checked, so for any flat recheck the wording with the council before work starts.
Windows in flat roofs over extensions and garages follow different logic, covered in roof windows in flat roofs.
What we check before ordering a window
A planning question is best answered before the window is bought. When you ask us about a roof window, the survey takes in the permission points as well as the roof, and photographs of the roof itself come with the written quote.
We start with the address: house or flat, conservation area or National Park, listed or not. Then the slope, front, rear or side, since a side slope brings the obscure glazing condition. Then the numbers: how far the chosen unit will stand off the covering and how high it will sit against the ridge. If any check points to an application, you hear before an order is placed. The deciding body is the council planning team based in Worthing Town Hall, or the South Downs National Park Authority where the house is inside the Park.
Planning and Building Regulations are separate
Planning governs how the building looks from outside. Building Regulations govern how it performs: the structure around the opening, the heat rating of the glass and, in a loft room, the way out in a fire. A window can be permitted and still need a building control application, or the other way round. We explain which consents apply and handle the Building Regulations notification where the work is notifiable.
Keep the glazing specification, the fitter's paperwork and dated photographs together in one folder, because a buyer's solicitor may ask for them when you sell. Cost follows access, covering, the type of window and the survey findings, and the quote is a single total that we keep good and fair. Typical UK fitting ranges are in roof window cost, and do roofers fit Velux windows covers who does the fitting.
