Garage conversion to habitable room

The conversion of a garage into a living space is treated as a change of use of a 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. The following points must be considered when converting a garage into a living space:

  1. Foundations
    A foundation must be provided to carry any additional masonry loads such as a new inner leaf to external walls or the garage door infill. The condition and suitability of the existing foundation/floor can be checked when the door infill area is excavated.

  2. Wall thickness
    If the existing wall is single leaf construction with piers it must be checked for stability and freedom from defects. If satisfactory it is likely the wall would be considered suitable (subject to c and d below).

  3. Weather resistance
    A wall of single leaf construction must be treated to provide satisfactory resistance to the passage of moisture. A waterproofing compound applied on the internal face and incorporated into a floor membrane may be an effective way of achieving this. The provision of an inner leaf to create a cavity wall will require a cavity tray at the base of the wall. Floors (new and existing) should also have a suitable damp proof membrane.

  4. Insulation
    It will be necessary to insulate the existing walls, roof and floor to habitable standards. Windows should achieve a 'U' value of 1.4 W/m²K and the use of low 'E' double glazed units would satisfy this requirement. The wall insulation value should be equal to 0.30 W/m²K, the floor 0.18 W/m²K and roof 0.15 W/m²K.

  5. Ventilation
    Windows must incorporate openable vents of an area equal to 1/20th of the floor area of the room, trickle vents to provide background ventilation of 8000mm². Generally a window of 0.33m² with a clear opening width or height of 450mm and no greater than 1100mm from floor level is to be provided if the new room can only be accessed through another room (for escape purposes). It is not possible to be precise in the advice we give regarding garage conversions as individual circumstances vary, please contact Building Control for further advice.

Last updated: Wednesday, 5 October, 2022.