A casing for openings in buildings with enhanced thermal insulation capacity includes a first tubular section bar which is fixed to a perimetrical wall delimiting the opening, and a second tubular section bar cooperating with the first tubular section bar in order to hermetically close the opening. The first and second tubular section bars are capable of supporting one or more front panels of an interface between an inner environment and an outer environment of the building. At least one of the first tubular section bars and the second tubular section bars presents a plurality of through openings which create within at least one of the tubular section bars a continuous flow of circulating air which, due to the temperature difference between the inner environment and the outer environment, forms a natural thermal barrier in any season.