Method for controlling an indoor climate of an inner space, said inner space being partly delimited by a floor, wherein an underfloor space, for example a crawl space, is present under the floor, wherein use is made of a flow-through insulation assembly that is arranged under the floor of the inner space and in the underfloor space, wherein the insulation assembly has a gas-tight chamber with a top wall, a bottom wall, and a perimeter, wherein the top wall is located under or against the floor of the inner space, wherein the top wall and the bottom wall are each substantially formed by a gas-tight film material, wherein a perforated top film and a perforated bottom film are further arranged in the gas-tight chamber, wherein the top wall, the bottom wall, the top film, and the bottom film have air-tight joints to the perimeter of the gas-tight chamber, so that a top cavity of the insulation assembly is delimited between the perforated top film and the top wall, a bottom cavity of the insulation assembly is delimited between the perforated bottom film and the bottom wall, and a flow-through space for gas is delimited between the perforated top film and the perforated bottom film, wherein the insulation assembly has a top opening that is connected to the top cavity, and a bottom opening that is connected to the bottom cavity, wherein use is further made of a ventilation system with at least one fan, wherein, for controlling the indoor climate of the inner space, the ventilation system is operated in order to supply a gas, for example air, to the gas-tight chamber of the insulation assembly via either the bottom opening or the top opening, said gas leaving the gas-tight chamber via the other one of the bottom opening and the top opening, so that the gas either flows from bottom to top or from top to bottom through the insulation assembly, wherein the gas flows via the associated bottom cavity, or top cavity respectively, through the bottom film or top film associated with said cavity into the space for gas flow-through between the bottom film and the top film and leaves said space through the other one of the bottom film and top film and then flows into the other one of the bottom cavity and the top cavity, wherein the gas then leaves said cavity and the gas-tight chamber via the associated bottom connection, or top connection. wherein use is made of a flow-through insulation assembly that is arranged under the floor of the inner space and in the underfloor space, wherein the insulation assembly has a gas-tight chamber with a top wall, a bottom wall, and a perimeter, wherein the top wall is located under or against the floor of the inner space, wherein the top wall and the bottom wall are each substantially formed by a gas-tight film material, wherein a perforated top film and a perforated bottom film are further arranged in the gas-tight chamber, wherein the top wall, the bottom wall, the top film, and the bottom film have air-tight joints to the perimeter of the gas-tight chamber, so that a top cavity of the insulation assembly is delimited between the perforated top film and the top wall, a bottom cavity of the insulation assembly is delimited between the perforated bottom film and the bottom wall, and a flow-through space for gas is delimited between the perforated top film and the perforated bottom film, wherein the insulation assembly has a top opening that is connected to the top cavity, and a bottom opening that is connected to the bottom cavity, wherein use is further made of a ventilation system with at least one fan, wherein, for controlling the indoor climate of the inner space, the ventilation system is operated in order to supply a gas, for example air, to the gas-tight chamber of the insulation assembly via either the bottom opening or the top opening, said gas leaving the gas-tight chamber via the other one of the bottom opening and the top opening, so that the gas either flows from bottom to top or from top to bottom through the insulation assembly, wherein the gas flows via the associated bottom cavity, or top cavity respectively, through the bottom film or top film associated with said cavity into the space for gas flow-through between the bottom film and the top film and leaves said space through the other one of the bottom film and top film and then flows into the other one of the bottom cavity and the top cavity, wherein the gas then leaves said cavity and the gas-tight chamber via the associated bottom connection, or top connection.