Whether you are planning a loft conversion, property extension or any other kind of building work, you will need to address the necessary paperwork. It is the same when you are adding skylights or roof windows to your existing roof.

Even in the case of a simple conversion with roof windows, you will need to be mindful of the existing building regulations for rooflights. In some cases, just adding roof lights may not require planning permission, but you will still do well to check with your local planning authority before the start of the project. Otherwise, you risk having to undo the project or incur a fine.

In this article, we will go over permitted development rules and planning permissions from a local authority for a new window that is installed on your roof structure.

Do you need planning permission for roof windows?

For many roof windows, you will not always require planning permission. The most straightforward fittings can do without one, including pitched roof windows and flat roof windows. This is because when you install a rooflight, the work is commonly carried out without the need for major structural changes.

Do I need roof light building regulations approval?

In general, you will need an approved document under the building regulations when installing a new rooflight or roof lanterns for these reasons:

  • The roof structure will need a new opening
  • The roof must be able to carry the weight, or else needs to be strengthened/have new support introduced
  • New rooflights need to be energy efficient and have sufficient insulation
  • If the new window is within close proximity to a boundary, fire performance must be considered

Important factors to consider when getting replacement windows

Here is what you have to consider when getting a new rooflight.

The structure

A rooflight is a window installed within a pitched roof or a flat roof normally to give more access to natural light. During the process, installers usually need to cut rafters and joists and have new support introduced at the cut ends, usually with double timbers called trimmers. The adjacent rafters may need to be strengthened to better support the load transferred from the cut areas. One way to achieve this is to fix a new rafter running the full length of the structure.

Weather proofing

The laminated glass and the edges of the installed rooflight require weatherproofing. The most common solution is lead flashing and proprietary kits supplied with the rooflight itself. You can seek advice from the installers and manufacturers of the rooflight.


Every room with a rooflight requires ventilation. The rooflight can be utilised for quick venting or background venting. It is also important to consider ventilation of the existing roof void so that air can flow freely.

Energy conservation

In regards to energy conservation dwellings must be energy efficient. One way of achieving greater energy efficiency is to minimise the heat loss from doors and windows. This is measured through the u value, which states how much heat is lost through the surface. Building regulations provide guidance on the maximum u value allowed for windows so any loft conversion project revolving around that needs to be in accordance.

Building regulations for skylights and u value

Building regulations in the UK set a standard for what the u value of buildings needs to be. This showcases the least energy efficient windows need to achieve, in order to be legal for installation. And while it is true that U value alone doesn't determine how good thermal insulation is, it is an important parameter to keep in mind.

Current regulations list the allowed u value for dwellings at 1.6 W/(m²K). This means that it is illegal to go for single-glazed units, which often have a u value of around 5. Double and triple-glazed windows are usually the go-to options.

If you are in doubt contact your manufacturer or installer for further information on the u value of your chosen windows.

Is My Roof Suitable For A Roof Window

Roof windows are a great option for loft rooms or spaces within the home that require more light. The installation process is commonly done by cutting one or more of the roof's rafters. Building regulations will generally allow the installation of new windows, but it is always well advised to check the planning regime in your local area before commencing any work. One of the most important requirements is having enough head height and floor space.

When you are doing any loft conversion or just one aspect of it by adding new skylights to your home, you will do well to check the current building regulations for what is permitted development and what requires permission from your local authority. When it doubt, always seek out further information before continuing with the project.

Topics and questions

What is the building regulation for skylight upstand?

In accordance with the building regulations, skylights have to protrude no more than 150 mm from the existing structure. Their pitch must be at least 3 degrees. This ensures the proper weather proofing.

Do I need building regs to fit a Velux window?

In most cases, you will not need planning permission to install a rooflight, or any other Velux window that is installed on the existing roof plane. However, when you install windows for more light, it is always best to contact your local planning authority and double-check regulations for further guidance.

Do you need planning permission to install rooflights?

When installing rooflights to get more natural daylight in your home, you don't need to apply for planning permission when certain building regulations requirements are met. Replacement windows must not protrude more than 150 mm above the existing structure. Alterations cannot be higher than the highest part of the roof ridge.

Do you need planning permission for skylight in the loft?

If you live in England and Wales, you don't need to apply for planning permission to install a skylight. However, installing the structure on a roof generally entails cutting part of the roof rafters, so the size and scope of the roof lights need to be sensible.

Are roof windows covered under permitted development?

Permitted development rules allow for some roof alterations, as long as there is no protrusion longer than 150 mm from the existing roof plane, no alteration is higher than the current highest point of the roof and side-facing windows are obscure glazed, with an opening at least 1.7 m above the floor.

Do you need planning permission for a balcony window?

Balconies and verandas are not permitted development and need planning permission. That is because they require extra support and need to adhere to certain fire performance standards. However, they improve the loft significantly and add value to the property. Certain balconies do not add extra floor space and so don't require planning permission.