You should insulate the entire house if you want to live comfortably. You will need to fortify your attic, walls, floors, and basement in order to stay warm during winter and cool during summer. Insulation prevents the entry of hot air from the outside during summer and the escape of warm air from the interior of the home during winter.
You can insulate the attic, basement, and flooring without much trouble using cellulose insulating machines. However, to properly insulate the walls, you must first have wall cavities to work with. Many older homes lack wall cavities, but even if you insulate every other part of the house, air can still creep in and out through unfortified walls.
It used to be common to build homes with solid walls. If you have an older home without cavities, don’t lose hope. You can insulate solid walls in two ways: internally and externally. For internal insulation of solid walls, you can fit insulation boards to the walls, a process known as dry lining. The insulation materials can be fixed to the inner side of the solid walls and then covered with cladding or plasterboards. The thicker the insulation boards, the better the insulation. Bear in mind, though, that if the solid walls are already thick, installing thick insulation boards plus the cladding will reduce the floor space of the house.
To insulate solid walls externally, apply insulation materials outside the walls with adhesive. The materials can then be covered with cement. Insulating the solid walls from outside may alter the appearance of the house. Many homeowners opt for internal insulation to preserve the look of their home.