Garages need to be well insulated, especially if you are using them as part of the home. Many people use garages as an extra living space, or the garage is a part of the home and so it needs to be kept well insulated in order to keep the house warm as well.
In order to keep your garage well insulated, make sure that any windows are double glazed and the walls are built using breeze blocks or another good quality material. The door is one of the most important aspects and should never be neglected. Select a door in a material like aluminium or fibreglass to help keep the heat in. These won’t be the cheapest options but they will make a really big difference to the temperature of your garage. Even if you go for a cheaper option, a new door will make a big difference as there will be fewer gaps where heat could escape.