Loft and garage conversions

Loft and garage conversions

You may wish to make alterations to your home to enhance the storage facilities or to increase the available living space. If you plan to make the loft space or garage more accessible or more habitable, and extensive work is likely to be required, for example installing a staircase or laying a new foundation, the Building Regulations (BR) are likely to apply.

It is recommended that you contact Building Control to discuss your proposal and to obtain further advice.

For more information, see our 'Building regulations' and 'Approval for building works' sections.

Boarding-out for storage

In most homes, the existing timber joists that form the 'floor' of the loft space (i.e. the ceiling of the rooms below) will not have been designed to support a significant weight (known as 'load'). The joists tie the pitched members of the roof together to prevent them spreading and support the ceiling lining of the rooms below.

An excessive additional load, for example from storage, may mean that the joists are loaded beyond their design capacity. If you decide to lay flooring boards over the existing joists in the loft space, then this may require a BR application to Building Control. Your local Building Control body will be able to advise you on this issue.

Creating a habitable space

The list below shows some typical examples of what is considered to be habitable spaces for a loft or garage conversion:

  • Bedroom
  • Play/Hobby room
  • Office/Study
  • Bathroom

If you decide to create a habitable space in an existing loft space or garage of a home, it is likely to require a range of alterations. Many of these could have an adverse impact on the building and its occupants if they are not properly thought out, planned and undertaken in accordance with the requirements of the legislation.

Fire safety

Any loft room should be separated from the rest of the home by fire resisting construction. This may involve:

  • Flooring – The ceiling fixed below the new room(s) may need to be upgraded to stop fire that might occur in the existing room(s) below from entering the new room.
  • Walls - The provision of new walls either at the first floor landing or in the loft space.
  • Doors - Any door formed within the wall(s) mentioned above is to be a self-closing fire door.

The exact details of these fire safety provisions depend on the circumstances. They will effectively result in the formation of a fire resisting box inside the house in which the occupants can wait with some protection until they are rescued from the fire via a rescue window.

If any part of the new construction faces a neighbouring property and is near to the boundary (or party wall) with that property it may well need to be constructed so as to give resistance to a fire spreading to or from the neighbouring property. The nature and extent of the construction to give this fire resistance will be dependent on the size of the dormer cheek and its proximity to the boundary.

Sound insulation

Sound insulation is required between habitable rooms. With a terraced or semi-detached house, the building control body may also ask for sound insulation between the converted loft and the neighbours' loft to be improved, and a test of the insulation to be carried out, but this will depend on the neighbours allowing access for the testers.

New external walls & roof

Weather protection

The materials forming the walls and roof should be able to provide protection against the elements. There are many different materials on the market for flat and pitched roofs. It is always recommended to gain advice from the manufacturers or Building Control as to the most suitable system to use for your roof.

Thermal insulation

The external walls and the roof of a building are required to help contain the heat inside it (for the conservation of fuel and power). To assist with the conservation of fuel and power these external elements of the building should be insulated to an appropriate degree. Whilst the overall construction contributes to this aim, it is usually necessary to provide insulation material, for example, in between the rafters or joists of the roof construction and in the cavities of wall construction.


Ventilation should be maintained to the existing roof structure to prevent condensation forming, which could cause the timber to rot and also reduce the performance of the thermal insulation. Additional venting may be required along the ridge of the roof to allow the air to travel from the bottom of the roof up to the top, between the existing rafters. A new flat roof on a dormer may also need to be ventilated. An alternative approach is to use warm-roof constructions that do not need ventilation.

Loft stair

Fire and general safety

To ensure adequate fire safety for the dwelling, a new stair serving the new room(s) will be needed. Where there is not enough room for a full traditional stair, it may be possible to use a 'space saving' stair. Retractable ladders or stairs are not normally acceptable.

For general safety reasons, there are specific criteria that a stair should be designed to.

Loft windows or skylights

Windows and skylights in loft conversions provide:

  • Thermal resistance
  • Weather resistance
  • A means of rescue from fire

For more information, see our 'Maintenance and renovation work' section.


Smoke alarms

A smoke detector should be installed on each floor landing and all detectors should be interconnected (meaning that they will all go off simultaneously and be heard on all levels of the dwelling).

The smoke alarm system should also be wired to a separate fuse, or to a lighting circuit – however, they will then need to have a battery backup.


Roofs should be effectively drained and any new bathroom or kitchen fittings should be adequately drained.

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