Conversion of garage to habitable room

The conversion of a domestic garage into a living space is a 'change of use' of part of the building. An application for approval under the Building Regulations must be made before work commences. The submission of a Building Notice is an appropriate way to achieve this, although a Full Plans application provides the house owner with more security about what work needs to be carried out prior to commencement on site. This information is for general guidance only and advice specific to your conversion is available from us on request. It does not cover conversions involving the installation of a toilet or bathroom for example.

The following points must be considered when converting a garage into a living space.

Foundations

A foundation must be provided to carry any additional masonry loads, such as when a new inner skin to external walls is built or when filling in the garage door with brickwork and a window. The condition and suitability of the existing foundation/floor can be checked when the door infill area is excavated.

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Wall thickness

If the existing wall is single skin construction with piers, it must be checked for stability and absence of defects. If satisfactory, it is likely that the wall would be considered suitable for structural purposes. However, see weather resistance and insulation below.

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Weather resistance

A wall of single leaf construction must be treated in some way to make it weatherproof. Common ways to do this are:

  • to dry line the wall using a moisture barrier linked to a damp proof course or membrane at floor level. Treated battens, insulation, and polythene backed plasterboard would complete the installation and

  • to provide a lightweight blockwork inner leaf (if the floor is adequate to support this) with appropriate insulation in the new cavity. The provision of an inner leaf to create a cavity wall will require a cavity tray at the base of the wall unless it is possible to create a 6"/150mm deep cavity below finished floor level between the new inner leaf and the external skin. Floors (new and existing) should also incorporate a suitable damp proof membrane (1,200 gauge polythene for example).

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Insulation

It will be necessary to insulate the walls, roof and floor to habitable standards. Windows must achieve a 'U' value of 0.18 W/m2/K. The wall insulation value should be equal to 0.35W/m2/K, the roof 0.16W/m2/K if pitched or 0.25 W/m2/K if flat and the floor 0.25W/m2K.

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Ventilation

Windows must incorporate openable vents of an area equal to 1/20th of the floor area of the room and 8,000mm2 of trickle vents to provide background ventilation are also required. A window with a clear opening of 450 x 733mm will be required (for escape purposes) if the new room can only be accessed via another room.

Roof space ventilation will usually be required when the garage roof is being insulated for the first time.

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Sound resistance

Any party wall between the garage and an adjoining property will have to adequately resist the passage of sound. A cavity or 9"/225mm masonry wall will usually be acceptable but a single skin of brickwork (4"/100mm thick) as is often found between neighbouring garages is not sufficient and will need upgrading. This will normally be done by adding an extra skin of masonry or timber stud, plasterboard and mineral wool.

Internal walls may also need to resist the passage of sound depending on the new layout.

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Electrical installation

Refer to Part P, Electrical Safety.

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Planning consents

In many cases the conversion of a garage to living accommodation does not require planning permission and will be regarded as 'permitted development'. However, in some cases permitted development rights were removed when planning permission was granted for the original construction of houses. In these circumstances planning permission will be required before you can carry out the work.

Where work is proposed to a listed building you should contact one of the Council's planning officers for advice as Planning and/or Listed Building Consent may be required. Please note that it is a criminal offence to carry out unauthorised work to a listed building even if the work is completely inside the property.

Garage conversions can be relatively expensive. If you are unsure whether or not the work you propose requires approval please contact the Building Control Service for advice. If you carry out work which requires approval without first submitting an application, you will not benefit from having the work independently inspected and you risk enforcement action. The lack of a completion certificate from the Council may affect the future sale of your home.

Please note that these guidance notes are for advice only and may not cover all situations. It is your responsibility to ensure that they are appropriate for use in your particular circumstance.