Skylight and Rooflight Planning Rules in Derby

For a house in Derby, a rooflight is usually covered by what planning law calls permitted development. The national rules are in the General Permitted Development Order. Class C of Part 1 covers any other alteration to the roof of a dwellinghouse, and that is the class that rooflights and roof windows fall under. The government's Planning Portal sets out the same rules for householders in plain language.

That is the good news. The catch is that permitted development comes with conditions, and a rooflight that breaks one needs a planning application. Derby City Council is the planning authority for the city, and its website, derby.gov.uk, is where applications are made.

For towns outside the city but inside our 30-mile area, the planning authority is usually the district or borough council covering that town. The rules of Class C are national, but Article 4 directions and local designations differ from place to place.

What permitted development is not

It is not a free pass. It is a set of conditions, and if the conditions are met, you do not need to ask. If one is not met, you ask. It also covers planning only. Building Regulations are a separate system, covered in a later chapter.

What this guide covers

The conditions for a house, what changes for flats and for listed buildings, what changes in conservation areas and World Heritage land, lanterns and flat roofs, and the order of steps if you need to ask the council. Each chapter stands alone, so jump to the one that fits your home.

Class C allows any other alteration to the roof of a house, which includes fitting a rooflight or roof window. It does not apply if one of the following is true.

• The alteration would protrude more than 150 mm beyond the plane of the original roof slope, measured from the outer surface of the roofing.
• The alteration would be higher than the highest part of the original roof.

There is also a condition on windows. Any window inserted on a roof slope that forms a side elevation of the house must be obscure-glazed. It must also be non-opening, unless the parts that open are more than 1.7 m above the floor of the room in which the window is installed.

What that means for a roof window

Most roof windows are designed to sit close to the roof covering, so they stay within the 150 mm limit. A flush-fitting unit on tiles is well inside it. A unit on a raised kerb may not be. The measurement is taken from the roof plane, so what matters is how far the finished unit stands above the original covering.

What that means for a side-facing slope

A side slope is a roof slope that forms a side elevation of the house rather than its front or back, as the end slopes of a hipped roof do. A gable roof has no side slope: its end is a wall. A rooflight on that slope has to be obscure-glazed, and if it opens, the opening part has to be high enough, more than 1.7 m above the floor, that it cannot be used to look out and across at the neighbour. This protects privacy. If you want a clear-glass opening unit on a side slope, that usually needs a planning application.

Original roof, not today's roof

The conditions refer to the original roof as built, or as it stood on 1 July 1948 for older homes. Earlier alterations by past owners do not reset the baseline. If the roof was altered by a previous owner, check what is recorded.

The rule that a rooflight is permitted development applies to houses. Householder permitted development does not reach flats or maisonettes, so adding or changing a rooflight in one normally needs a planning application. In practice, many flat roofs and roof spaces belong to the freeholder, who also needs to agree. Check your lease and the building's management arrangements before you plan anything.

Flats in converted houses

Derby has many large Victorian and Edwardian houses that have been split into flats. A top-floor flat in one of these buildings may seem to have a roof of its own, but the planning position follows the flat's status, not the roof's look. Treat a flat as a case where you ask the council first.

Listed buildings

If your building is listed, most changes to it, including roof alterations, need listed building consent. That is separate from planning permission, and it applies even where the work would otherwise be permitted development. Historic England explains the system at historicengland.org.uk, and the council's conservation officers can advise on a specific building. Conservation-style rooflights are made to sit flush with the roof and to look like the original, and our page on conservation rooflights in listed buildings goes deeper.

Buildings that are not dwellinghouses

Small commercial jobs are welcome, but permitted development for shops, offices and other uses follows different classes. Treat a non-residential building as a case where you check with the council before anything is ordered.

Conservation areas matter for rooflights because the council can remove permitted development rights there. It does this by making an Article 4 direction, which brings back the need for a planning application for work that is normally allowed. Whether a direction covers your street is a question only the council can answer for sure, so ask before you plan.

Even without an Article 4 direction, a conservation area changes the way the council looks at an application, because it has a duty to preserve or enhance the character of the area. A rooflight on a front slope facing the street is the most sensitive case. A rooflight on a rear slope out of public view is usually less so.

Derby's designations

The Derwent Valley Mills World Heritage Site follows the Derwent through Derby, Darley Abbey included, then heads north to Milford, Belper and Cromford. Parts of Derby also sit inside conservation areas. We do not list them here, because boundaries and directions change, and the council's maps are the reliable source. Our page on conservation areas and rooflights in Derby goes through how to check, and what kind of unit tends to be accepted.

What to ask the council

• Is my address inside a conservation area?
• Is there an Article 4 direction that removes permitted development for roof alterations?
• Is the building listed, or in the setting of a listed building?
• Would a rooflight on the rear slope be treated differently from one on the front?

Peak District edges

Some of the towns within our 30 miles lie in or beside the Peak District National Park. In those places the planning authority may be the National Park Authority, and the rules for protected landscapes can be tighter. We check which authority applies before we plan.

Flat roofs and extensions raise a slightly different question. A flat rooflight on a kerb, or a roof lantern on a single-storey extension, stands up from the roof by more than a roof window on a pitched slope does. Where the unit rises more than 150 mm above the plane of the roof, it can fall outside Class C. A lantern is also taller than most flat rooflights, so check before assuming. Our page on roof lanterns covers the shapes and heights.

New extensions

If the lantern is part of a new extension, the whole extension is often judged together. An extension built under permitted development has its own limits on height and size, and a lantern forms part of the roof of the extension. If planning permission is being applied for anyway, put the lantern on the drawings so that it is approved with the rest. A lantern added later to a roof that was approved with a flat or low-profile finish is better checked first.

Existing flat roofs

Adding a flat rooflight to an existing flat roof is usually a smaller step. The height above the roof plane is the thing to measure, and the kerb is part of that measurement. For the practical side of fitting one, see adding a rooflight to an existing flat roof. New extensions are covered in rooflights for single-storey extensions.

Walk-on and ground-level rooflights

A walk-on rooflight set in a terrace or a courtyard is not a roof alteration in the same sense. Even so, a flat rooflight is raised on a kerb or upstand, so the unit can still stand more than 150 mm above the roof surface; measure it before assuming it is permitted development. Other rules can apply, such as those on balconies, raised platforms and overlooking, so ask if the setting is unusual.

Planning and Building Regulations are different things, and passing one does not satisfy the other. A rooflight can be permitted development and still need Building Regulations approval. A rooflight can also need planning permission and be fully compliant with the Regulations. You need to deal with both.

New openings

Cutting a new opening alters the roof structure, which makes it building work. Approval comes from the local authority or a registered building control approver, the term in use since April 2024. Where the job is notifiable, we make the notification and fit to current Building Regulations.

Replacements

A straight swap of one rooflight or roof window for another counts as controlled fitting, so Part L, the energy part of the Regulations, applies to the new unit. The figures sit in Approved Document L on gov.uk. The ceiling for a roof window is 1.4 W/m²K, and for a rooflight, lanterns included, 2.2 W/m²K. A competent person scheme can be used to self-certify a replacement. Our guide to rooflight U-values explains what the numbers mean in a room.

Escape and safety

Where the rooflight serves a loft room, Approved Document B decides whether it can be the way out in a fire. That works only where the room sits no higher than 4.5 m from the ground, with a clear opening of 0.33 m² and no side shorter than 450 mm. Two-storey houses with a loft conversion need a protected stair. Bungalows and chalet bungalows with rooms in the roof can use a roof window, as long as that height limit is met.

No daylight rule

Houses in England face no daylight test under the Building Regulations, so a rooflight is never needed to pass on light. That is another reason planning and Regulations are separate questions.