Building Control - Garage Conversions

The following guidelines are to advise you of certain requirements if you are considering converting your garage area into a habitable room. This advice is given in general terms and will not cover all possible factors.

For further information please contact Building Control Services


A foundation may be required to carry any additional masonry loads, such as a new inner leaf to external walls or where a garage door is to be infilled. The condition and suitability of the existing foundation/floor can be checked on site.

Existing 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 structurally suitable but also check the points below on weather resistance and insulation.

Weather resistance

A wall of single leaf construction should 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 may require a cavity tray at the base of the wall.


It will be necessary to insulate the walls and roof to habitable room standards. Existing external walls, roofs and floors will generally need to be provided with additional insulation. Typically 275 mm “Rockwool” or similar to a pitched roof.120 mm of “Cellotex” or similar to walls and 75 mm of “Cellotex” or similar to the floor. For precise thickness you should contact the manufacturer. Windows should be double glazed with Low “E” glass.


Windows should incorporate openable vents of an area equal to 1/20th of the floor area of the room, and trickle vents to provide background ventilation.

Means of escape in case of fire

Where the new room does not have a door direct to an external place of safety away from the house or access to a hall or lobby, the windows will need to be of a suitable size and configuration to permit escape. The clear opening should not be less than 0.33m sq in area with any one dimension not less than 450mm and a maximum window cill height of 1100 mm.

Additional permission that may be required