The invention relates to a method of constructing a building, comprising the step of providing a skeleton for a building wall of the building. The skeleton includes at least upright building elements such as columns or dividing walls. At least one lightweight, heat insulating and fire retarding wall element is placed between each adjacent pair of said columns. The columns are covered to provide substantially closed wall surfaces. The wall surfaces are covered with a covering layer having properties so as to provide fire-resistance to the complete wall. The covering layer on the inside wall surface may include a base layer of modified resin mortar, and a top layer of plaster mortar. The covering layer on the outside wall surface may include a base layer of modified resin mortar and a top layer of mineral mortar. Lightweight, heat insulating floor elements are placed and interconnected, and supported if necessary, and thereafter structural fill-material, such as concrete, is poured onto the floor elements to form a floor. The invention also includes a building, and wall and floor elements.