Sunsquare: The market leaders in skylight and roof light design and installation


In England and Wales, you do not normally need to apply for planning permission for the insertion of new roof windows subject to the current limits and conditions stipulated by the government’s Planning Portal under Schedule 2, Article 3, part 1, class C permitted development.

This includes:

  • Any alteration cannot project more than 150 millimetres from the existing roof plane i.e. any new flat roof skylights cannot project more than 150 millimetres.
  • No alteration can be greater than the highest part of the existing roof.
  • Side-facing windows must be obscure glazed with any opening to be made 1.7 metres above the floor.

If your project fails to comply with one or more of the above, your development would not be permitted and a second application would need to be resubmitted following amendments to your plans.

Roof windows and Listed buildings and conservation areas

If the property you want to install a new skylight is a listed building or in a designated conservation area, you should check first with your local planning authority before carrying out any work.

Additionally, there may also be an “Article 4 Direction” or any other type of planning restriction that means certain works which could normally be undertaken will be the subject of control.

It’s important to note that planning laws in Scotland are rather different. Planning permission for roof windows is very often required for even the most straightforward of skylight designs. Scottish property owners should contact their local authority to ascertain the best way forward.

Similarly, home owners in Ireland should also contact their local authority for advice as you should make absolutely certain that you don’t need planning permission for your roof window before you begin making alterations. Failure to obtain permission where it is required can result in penalties as significant as imprisonment.

Building regulations

The removal, addition or alteration of a skylight can potentially impact how a roof works, resulting in unplanned movement. When making any aesthetic improvements to your roof it’s critical that care is taken to ensure the roof continues to perform as it should and without any movement.

Even if planning permission for a new roof window is not required, building regulations cannot be ignored. By law, any building or structural modification work must comply with building controls which stipulate minimum standards for design and safety.

There are two sets of building regulations for roofs; work on an existing roof and the construction of a new roof e.g. for an extension.

Be sure to pay particular attention to Parts J and L of Building Regulations; these deal with energy efficiency, thermal insulation and the protection of buildings against the threat of fire.

Approval under the Building Regulations will generally be needed for the installation of a new rooflight for the following reasons:

  • To install a new rooflight, the roof structure will often need to be altered to create the opening.
  • The roof will have to be able to carry the weight of the new skylight. If the roof is not able to do so it will need to be strengthened prior to installation.
  • Any rooflight installed must prove it has sufficient insulation against heat loss with effective energy performance.
  • In the event a skylight is in close proximity to a boundary, its fire performance must also be taken into consideration.

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Roof structure

To install a rooflight in a roof you will often need to cut part of one or more of the roof’s rafters or joists away. You will need to fit a new support for the cut ends of the rafter or joist in question. Adjacent rafters or joists may also need strengthening as they will be supporting the load transferred from the cut rafters or joists.

Ventilation and energy performance

Any room that a skylight is designed to serve will also need to be well ventilated. This can be achieved using the skylight itself for both rapid and background venting.

In terms of energy performance, any window or door must comply with the minimum requirements of the Building Regulations in relation to the amount of heat that can pass through a window or door, including the frame.

This is known and measured as a U-Value. This U-Value should not be exceeded. At Sunsquare we can accurately calculate the U-Value of each of our BSI-accredited skylights.

However, for more information on the maximum U-Value allowed you can refer to Approved Document L-1B, Table 1.

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