In order to insulate the attic, you need to carry out a number of rather difficult manipulations. This room is only warm if all the roof slopes are reliably closed by the insulation. You can cope with this task with the help of such material as polystyrene foam. It is characterized by practicality and simplicity of laying. It must be attached directly to the rafter system.
But before that, a crate is equipped, which is a system of horizontally fixed bars. They need to lay a layer of waterproofing on them. It uses a polyethylene film for her. The main thing is that all joints are reliably fastened.
Then move on to the installation of insulation. In order to fix the polystyrene foam, in this case you need to use screws. The joints between the sheets of insulation are closed with an mounting ribbon. After that, form the base for finishing, for example, using drywall.