As the boxes are 27cm deep they can stick out on both sides of a thin wall or ceiling. It can also be installed flushed or asymmetrically, but may not stick out more than 8.5cm at one side. Consequently, the wall would have to be at least 18.5cm thick for a flushed installation. In ceilings the box may not stick out more than 6cm. Therefore, the ceiling then must be at least 21cm thick. Assymmetrical installations can be made in very thin walls as well.