Insulating a garage reduces the cold that emanates from the unheated space and improves comfort in both the garage and adjoining rooms. The approach depends on whether the garage is integral to the house or detached, and which elements are causing the most heat loss.

Insulating Garage Walls

For single-skin brick or block garage walls, the most practical insulation method is to install a timber stud frame on the inside face of the wall, fill it with mineral wool or rigid foam insulation, and line with plasterboard. This adds approximately 100mm to the wall thickness per side. For cavity wall garages, injected or blown insulation can be added to the cavity in the same way as a house. Wall insulation makes a significant difference to the thermal performance of an integral garage and to the temperature of rooms sharing walls with it.

Insulating the Garage Roof or Ceiling

For a flat-roofed garage, insulation can be added to the roof structure from above as part of a roof refurbishment, using a warm flat roof construction with rigid foam above the existing deck. For a pitched-roof garage used as a cold loft, insulation at ceiling level (between and over the ceiling joists with mineral wool to 270mm total depth) is the most cost-effective approach. If the loft space is used, insulation at rafter level creates a warm loft suitable for habitable use.

Insulating the Garage Floor

As covered in the garage floor guidance, floor insulation requires laying rigid foam board over the existing slab and covering with a floating deck. This raises the floor level, which must be managed at the door threshold and any internal steps.

Insulating the Garage Door

An uninsulated steel garage door is a significant cold bridge. Fitting a purpose-made insulation panel kit to the inside of the door adds meaningful thermal resistance at modest cost. Combined with a good perimeter seal to close gaps, an insulated door with full sealing reduces door-related heat loss dramatically.

Summary

Insulate garage walls with a stud frame and mineral wool or rigid foam plus plasterboard lining. Insulate a flat roof with warm roof construction from above; insulate a pitched roof ceiling at joist level. Insulate the floor with rigid foam under a floating deck. Insulate the door with a purpose-made kit. For integral garages, prioritise walls and ceiling shared with the house first for maximum impact on adjoining room temperatures.