All You Need to Know - Building Regulations


What do extensions and loft conversion building regulations cover?


UK building regulations will cover a number of elements of a loft conversion, including the floor, the structural soundness and the insulation. The regulations are there to ensure that the new structure is completely safe.


Using your loft as a living space will mean that the floor has to hold a lot more weight than it did originally. As such, the structural strength of the new floor of your loft conversion must be sufficient enough to hold the added weight, or it will not meet building regulations. Any joists and load-bearing walls must be strong enough to support the extra weight, and you will also have to install steel beams to support the new joists.

Fire doors and fire escape

There must be the provision of a safe escape route from your loft conversion in case of fire. Each room of the conversion must have an appropriate escape window, and each window should be easily accessible, with the use of a ladder, from outside. Furthermore, fire alarms should be installed, there must be a self-closing fire door, any new floors and walls must be capable of resisting fire and any glazing used in doors should be fire resistant.

Stairs and access

The stairs to the new floor of the loft conversion must be safely designed. Any staircase to the new living space must be wide enough to allow anyone to use them easily in case of an emergency.

Headroom and ceiling height

Your loft conversion must offer sufficient headroom and a high enough ceiling height for it to be a practical living space. This applies both to the living area itself, and the staircase up to the conversion as well.

Insulation depth, energy efficiency and U-Value

Any dwelling should be energy efficient. Any walls, roof slopes, ceilings and new windows and doors installed in a loft conversion will be measured to determine how much heat passes through the glass and framework. The amount of heat lost must not exceed a certain limit, known as the ‘U-Value’. Even if the rest of your existing property doesn’t comply with this standard, your new loft conversion still must have sufficient insulation to meet the building regulations.

In terms of keeping sound transference to a minimum, insulation between the conversion and the rooms below must be sufficiently effective, as must the insulation in any new internal walls. If you live in a terraced or semi-detached house, you may also find that you have to improve the insulation between yours and your neighbours’ lofts.


Your new loft conversion must be ventilated properly to ensure that it meets building regulations. There should be a window that is a twentieth of the total floor area of the new living space, and there should be a mechanical fan of sufficient power if you are installing a bathroom. The roof void must also be ventilated to prevent condensation.

The information provided about loft conversions and building regulations above is designed as a brief guide to get you started thinking about what you might need to do to comply and get your conversion passed. However, each conversion will be judged individually. If you have any questions about loft conversions and building regulations in your area, you should call your local authority. Abbey Lofts will be able to provide further advice also.

All You Need to Know - Planning Premission

Will I Need Planning Permission for
a Dormer Loft Conversion?

In the majority of cases, adding a dormer loft conversion to a house falls under permitted development and will not require planning permission. It is however important to be aware of the specific conditions and limitations of permitted development, and if there is any doubt as to whether your proposed conversion passes the permitted development tests we recommend obtaining a Lawful Development Certificate from your local authority. The LDC is not the same as planning permission, but does provide you with written proof that your loft conversion is lawful should questions be raised at a later date when you come to sell your house.

You will require planning permission if:

  • The house is situated on designated land. A roof extension does not fall into the category of permitted development if a property situated within an area of outstanding natural beauty, conservation area, national park or world heritage site.

  • The volume of the new addition exceeds the limits of permitted development. The limits are currently 40 cubic metres for terraced houses, and 50 cubic metres for both detached and semi-detached houses. These limits apply to the size of the ‘Original House’ which refers to the house as it was on 1st July 1948, or if your property was constructed after this date, the size of the house when it was first built.

  • The dormer extension is to be built on the part of the roof that fronts the highway. Any extension beyond the plane of the existing roof slope of the principal elevation may only be constructed on the rear or the hipped side of the roof under permitted development rules.

  • The height of the proposed dormer extension will exceed the height of the existing roof.

  • The materials you plan to use in the construction of your loft conversion are not in keeping with the appearance of the existing house.

  • The dormer loft conversion includes a balcony, veranda or raised platform.

  • The loft conversion includes side facing windows overlooking neighbouring properties. To fall within the conditions of permitted development, any side facing windows must be obscured glass, and only able to open at a height of 1.7 metres above the floor of loft room.

  • The proposed dormer extension reaches less than 20cm from the original eaves when measured along the roof plane.

  • Bats are using the building. As a protected species, a licence is required to carry out work on any building which may disturb or affect the bats’ welfare.

Will I Need Planning Permission for
an Extension?

An extension or addition to your house is considered to be permitted development, not requiring an application for planning permission, subject to the following limits and conditions:

  • No more than half the area of land around the "original house" would be covered by additions or other buildings.

  • No extension forward of the principal elevation or side elevation fronting a highway.No extension to be higher than the highest part of the roof.

  • Single-storey rear extension must not extend beyond the rear wall of the original hous by more than three metres if an attached house or by four metres if a detached house.

  • In addition, outside Article 2(3) designated land and Sites of Special Scientific Interest the limit is increased to 6m if an attached house and 8m if a detached house until 30 May 2019.

  • These increased limits (between 3m and 6m and between 4m and 8m respectively) are subject to the prior notification of the proposal to the Local Planning Authority and the implementation of a neighbour consultation scheme. If objections are received, the proposal might not be allowed.

  • Maximum height of a single-storey rear extension of four metres.

  • Extensions of more than one storey must not extend beyond the rear wall of the original house by more than three metres.

  • Maximum eaves height of an extension within two metres of the boundary of three metres.

  • Maximum eaves and ridge height of extension no higher than existing house.

  • Side extensions to be single storey with maximum height of four metres and width no more than half that of the original house.

  • Two-storey extensions no closer than seven metres to rear boundary.

  • Roof pitch of extensions higher than one storey to match existing house.

  • Materials to be similar in appearance to the existing house.

  • No verandas, balconies or raised platforms.

  • Upper-floor, side-facing windows to be obscure-glazed; any opening to be 1.7m above the floor.

  • On designated land no permitted development for rear extensions of more than one storey.

  • On designated land no cladding of the exterior.

  • On designated land no side extensions.

  • The term "original house" means the house as it was first built or as it stood on 1 July 1948 (if it was built before that date). Although you may not have built an extension to the house, a previous owner may have done so.

  • Designated land includes conservation areas, national parks and the Broads, Areas of Outstanding Natural Beauty, and World Heritage Sites.