Planning Permission

You do not normally need to apply for planning permission to re-roof your house or to insert roof lights or skylights as the permitted development rules allow for roof alterations subject to the following limits and conditions:

  • Any alteration to project no more than 150 millimetres from the existing roof plane.
  • No alteration to be higher than the highest part of the roof.
  • Side facing windows to be obscure-glazed; any opening to be 1.7m above the floor.
  • The permitted development regime for solar panels has different limits on projections and in relation to protected areas.

Solar panels: View guidance on the planning and building regulations regime for solar panels.

Please note: the permitted development allowances described here apply to houses not flats, maisonettes or other buildings. You are viewing guidance for England. View guidance on flats and maisonettes here.

Protected Species

Work on a loft or a roof may affect bats. You need to consider protected species when planning work on this type. A survey may be needed, and if bats are using the building, a licence may be needed.

Building Regulations

There are two sets of building regulations for roofs:

Work to an existing roof

If you want to carry out repairs on or re-cover less than 25 per cent of the area of a pitch or flat roof, you will not normally need to submit a building regulations application. You will need approval, however, if:

  • You carry out structural alterations
  • The performance of the new covering will be significantly different to that of the existing covering in the event of a fire
  • You are replacing/ repairing more than 25 per cent of the roof area, in which case, the roof thermal insulation would normally have to be improved.

The removal or alteration to any roof elements could affect how the roof works and cause movement to occur. Movement could cause cracks to occur in the walls and, possibly, the eventual collapse of the roof. When performing work on any roof, care should be taken to ensure the roof will continue to perform effectively and without any movement.

Existing Pitched Roofs

The existing roof structure that forms the loft space has a number of timber elements that make the overall pitch. Each element enables the roof to span across the building and support the tiles/covering on top as well as being able to transfer the loads (weight) created by any wind and snow down to the walls.

Listed below are the typical elements of a pitched roof:

  • Ridge Board – This forms the apex of the roof and is where the rafters are fixed to both sides.
  • Rafters – These are the timbers that form the main pitch to the roof and support the tiles and battens.
  • Purlins – These are long pieces of timbers that are normally seen half way along the rafters and act like beams to reduce the span (unsupported length) of the rafters.
  • Struts – These support the purlins.  They are fixed at an angle with one end connected to the purlin and the other on to a load bearing wall or a timber spread across ceiling joists. These are the diagonal timbers seen in the roof.
  • Ties – These are timbers which stop the roof from spreading and form an A-frame shape.  They can either be the ceiling joists (as described below) or can be fixed half way up usually above the purlin and are fixed horizontally from front to back. (Common in terraced houses).
  • Ceiling Joists – These can act as ties, but mainly support the ceiling below.  Their sizes are usually relatively small and will not be able to take the load of any typical room used in a house.

Existing Flat Roofs

Flat roofs are more simple and generally consist of joists that span the gap between two walls. These are covered by panels which, in turn, are covered in felting or other such coatings as required.

Further information


After a period of time the roof on existing buildings will need to be replaced. In most situations, this work will need Building Regulations approval.

Flat Roofs

Some repairs to flats roofs will not require an application for approval under the Building Regulations. However, if the roof with integral insulation is to be replaced then you may be required to upgrade this ‘thermal element’ of the structure and reduce the amount of heat that was originally lost, by upgrading the insulation.

Pitch Roof

If the existing roof covering is to be replaced with a different material to its original for example, slate to tiles, then approval under the Building Regulations is likely to be needed to ensure the roof will be adequate in terms of structural stability (applicable where the replacement tile will be significantly heavier or lighter than the existing), and also meets requirements in respect of fire safety and energy efficiency (see above).

If the new roof covering is significantly heavier or lighter than the existing one, the roof structure may need modifying and/or strengthening, and you are advised to check with a structural engineer or surveyor before commencing with works.

Energy Efficiency

As a roof is defined as a thermal element, the work to re-cover a roof should also include for improving the thermal insulation properties of the roof.


A rooflight is a window that is installed within a pitched roof or flat roof normally to give more light to rooms or spaces within the home.  Approval under the Building Regulations will generally be needed for the installation of a new rooflight for the following reasons:

  • To install a rooflight, the roof structure will generally need to be altered to create the opening.
  • The roof will have to be able to carry the load (weight) of the new rooflight. If the roof can not do this then it will need to be strengthened.
  • Any rooflight that is installed will need to prove that it has sufficient insulation against heat loss i.e. is energy efficient.
  • If the rooflight is in close proximity to a boundary, the fire performance of the rooflight will need to be considered.


To install a rooflight in a roof generally entails cutting part of one or more of the roof’s rafters or joists away. The cut ends of the rafter/joist will need to have new support introduced – usually achieved by fixing two pieces of timber together which span across the new opening on either side. These double timbers are called ‘trimmers’.

The adjacent rafters or joists to which these trimmers are fixed may also need to be strengthened as they will be supporting the load transferred from the cut rafters or joists.  This strengthening can be achieved by fixing a new rafter or joist to them which must also run the full length.

Weather Proofing

Once a rooflight is installed the edges (where the rooflight meets the roof) will require weather proofing as well as the glass of the rooflight itself.  This is commonly carried out by using lead flashing or with proprietary kits supplied with the rooflight.  Manufacturers of rooflights may be able to advise on how this can be carried out.


A room that the rooflight is to serve will need to be ventilated.  Ventilation can be achieved by using the rooflight for both rapid and background venting.

Ventilation of the existing roof void(s) will have to be considered as air must still be allowed to flow from one to another.


Energy Conservation

Dwellings are required to be energy efficient. A method of achieving greater energy efficiency is to take steps to reduce the amount of heat that is lost through the glazing in both windows and doors.

If you are to install windows and doors you should be aware that they need to comply with the requirements of the Building Regulations in relation to the amount of heat that can pass through the door or window, including the frame, which is measured as a U-Value.  This U-value should not be exceeded.  For information on the maximum U-Value allowed please refer to Approved Document L-1B, Table 1.

 Insulation and thermal elements

Making significant changes to thermal elements (walls,roodor floors) would normally require Building Regulations approval and require the thermal insulation of the element to be upgraded to a reasonable standard. Walls are defined by Regulation 2(3) of the Building Regulations 2010  as being thermal elements.

The extent to which the work on the element is controlled and the amount of upgrading needed depends on the particular circumstances of the thermal element. Generally, when it is renovated then it should be upgraded, where it is cost effective to do so, to the standard set out in the Approved Document. See section 5 and Appendix A of Approved Document L1B.[a1]

The definition in Regulation 2(3) is extracted here for convenience from the Building Regulations 2010 

(3) In these Regulations “thermal element” means a wall, floor or roof (but does not include windows, doors, roof windows or roof-lights) which separates a thermally conditioned part of the building (“the conditioned space”) from:

     (a) the external environment (including the ground); or
     (b) in the case of floors and walls, another part of the building which is:
          (i) unconditioned;
          (ii) an extension falling within class7 of Schedule 2; or
          (iii) where this paragraph applies, conditioned to a different temperature,

and includes all parts of the element between the surface bounding the conditioned space and the external environment or other part of the building as the case may be.

(4) Paragraph (3)(b)(iii) only applies to a building which is not a dwelling, where the other part of the building is used for a purpose which is not similar or identical to the purpose for which the conditioned space is used.

Further guidance on this is available in Approved Document L1B covering:

  1. Guidance on thermal elements (Section 5 pages 17-18)
  2. Explanation of when renovation works trigger requirement for upgrading insulation and what additional work may be required.(see Appendix A  and Table A1 pages 21-23)

You should fully consult the Regulations and the Approved Document and, if you are in any doubt, seek advice before commencing work. The definition of a thermal element does not include windows, doors, roof windows or rooflights.

Pitch Roofs

Insulation can be placed between the ceiling joists. Again, the thickness will vary depending on the material you choose to use.

If the roof has no ceiling then the insulation can be placed between the rafters and ventilation maintained as described above – in which case the ridge should also have vent tiles installed to allow for through ventilation.

Further guidance on insulating roofs can be found in Approved Document L1B, Table A1.

Conversion projects

When converting areas to liveable space then it is likely that any existing roof needs to be checked for adequacy in terms of weather resistance and thermal insulation.

If the underside of the roof (the ceiling) is to be lined with plasterboard then the resulting void may also need to be ventilated.

Flat roofs

The roof will need to be ventilated. Typically, a 50mm gap should be maintained between any insulation and the underside of the roof.  Through ventilation is then achieved by incorporating eaves venting.

If the roof is to be re-covered then the insulation can be installed on top of the joists making a ‘warm deck’ roof (check with manufacturers for details).  This avoids the need for ventilation and the roof covering can be re-applied over the top.

Pitch Roofs

Insulation can be placed between the ceiling joists. Again, the thickness will vary depending on the material you choose to use.

If the roof has no ceiling then the insulation can be placed between the rafters and ventilation maintained as described above – in which case the ridge should also have vent tiles installed to allow for through ventilation.

Constructing a new roof (e.g. for an extension)

A new roof will be required to:

  • resist weather
  • resist the spread of fire from one property to another
  • be able to support loads (weights)
  • provide resistance to heat loss (insulation)
  • be ventilated to protect from condensation (in most cases)
  • have adequate drainage

There are generally two types of roof construction used:

  • Pitch roof – This is where tiles or slates are used and a void is usually created underneath.
  • Flat roof – This usually consists of felting which has a slight fall to allow rain water to drain off.

To enable compliance with the requirements of the Building Regulations to be demonstrated, full details of the new roof will be needed – including materials and their dimensions and performance properties.


The materials used to cover the roof should be durable and capable of resisting the elements of the weather.  With a pitched roof the type of tile or slate you wish to use will be partly governed by how steep or shallow the slope is.  If the roof is close to a boundary, which is often the case, the roof should also have properties to limit the risk from fire spreading across the boundary.


Not all roofs need to be ventilated. Ventilation is not required to a warm roof system, which is where the insulation is placed above the joists or rafters.   Otherwise ventilation is required and this is known as a ‘cold roof system’.

When ventilating a roof the air should be able to enter at one end and travel through to the other end where it can exit.

Further Information

Weight (Loading)

The loads (weights) to be supported are from various sources:

  • Materials: This would include tiles, battens, felt, insulation etc
  • Weather: e.g. wind, snow and rain
  • Maintenance: A person needing to access the roof in order to repair items

Wind Load

The roof should be tied down to the structure to stop it from lifting in times of strong winds. This is normally achieved by providing straps that are approximately 1.2m long with a cranked end which is fixed to the wall plate (to which the roof timbers are fixed) and then the inner skin of the wall at every 2.0m centres.


The timbers that make a pitch roof (rafters), will always want to spread apart.  Ceiling joists are a way of stopping this as they are fixed to the bottom end of the rafters and stop them from pulling apart. However, if you wish to take away the ceiling and be able to see roof, then another system should be used to tie down the rafters to the walls and stop them from spreading. For a roof that is to be exposed with no ceiling joists, you may wish to seek advice from an engineer.

Thermal resistance (Insulation)

There are two ways to insulate a roof:

Warm Deck – this is where the insulation is placed on top of the rafters/joists and the roof covering is then placed over the insulation. No ventilation is required for these types of roofs.

Cold Deck – this is where the insulation is placed between the joists/rafters or in between the ceiling joists in the case of a pitch roof. Ventilation is required for these roofs.

Flat roof

  • Warm Deck – The type of insulation for this is usually of a rigid type and the thickness will vary depending on the manufacturer’s specifications.  This is placed over the roof joists and an board (normally external ply) is laid on top. (Thickness varies according to the manufacturer’s specifications).  The roof covering is then laid over the ply.
  • Cold Deck – The thickness of insulation required will vary depending on the material you decide to use and the manufacturer’s specification.  A ventilation gap, usually 50mm, should be provided between the top of the insulation and underside of the roof covering to allow the air to flow across.  Ventilation openings (either at the eaves or upstand).  A vapour membrane should be added to the underside of the insulation and tacked to the joists before applying the plasterboard.

Pitch Roof

  • Warm Deck – The insulation is placed over the rafters and then a felt is placed on top.  The battening and tiling is then fixed down over.  The thickness of insulation will vary depending on the manufacturer’s specification.
  • Cold Deck – The insulation can be placed between the rafters or it can be placed between the ceiling joists.  The thickness of insulation in both cases will vary depending on the material you use and manufacturer’s specification.  The roof should have vents installed along the eaves to both front and rear or from side to side.  In the case where the insulation is placed between the rafters then vents should also be placed along the ridge.


This is an introductory guide and is not a definitive source of legal information. Read the full disclaimer here.

This guidance relates to the planning regime for England. Policy in Wales may differ. If in doubt contact your Local Planning Authority.