The SP-E system was designed first and foremost to provide protection against heat loss. Highly acclaimed, especially by the Passivhaus Institut (passive house institute) in Darmstadt, which issued a recommendation for employing both solutions for boxes of 165 mm and smaller in passive buildings. The prerequisite condition is, above all, proper installation in a pre-insulated lintel, according to the manufacturer’s guidelines. Additionally, window joinery should comply with the right specifications, e.g.: the Uw overall heat-transfer coefficient should be lower than 0.80 W/(m2K) and Ug windowpane coefficient should not exceed 0.70 W/(m2K). An additional advantage of flush-mounted roller shutters is the possibility of including an independently operating mosquito screen, which also provides protection against insects.