What is the most effective way to insulate an old garage?

I would like to insulate my garage better. At the moment the sides are single brick plus breeze blocks (internally), but there is no cavity. It is only single brick with a pitched roof at the back of the building. How do I insulate the structure effectively so I can use the space more?

Is your garage integral to the rest of the house or is it a detached structure? If it’s the latter, and therefore separate from any living areas, then you just need to line the walls with PIR insulation boards and tape up the joints as required. If it’s an integral garage, you will need to be more careful as just fitting layers of rigid foam boards to your walls can affect the dew points and lead to internal condensation and damp issues.

Using rigid foam will also encroach on internal space because it’s quite thick, so consider multi-layer foil laminate insulation to save space. It costs a bit more but performs very well, so can be excellent value. Fit it to timber battening affixed to the inside of the external walls and cover over with plasterboard.

Remember to fit a vapour control barrier, such as polythene sheeting, beneath the plasterboard. Suppliers can advise on correct way to fit their products and you can always speak to your local building control officer to determine what they would want to see as best practice in your situation.