The easiest way is to fill the boards on the ceiling, and with an edge down. The boards should be the same in size: the width should be equal to the double layer of insulation, and the thickness can be about 40 mm. The boards are stuffed from each other at a distance, as you probably guessed equal to the width of the insulation. Then, the space between the boards is filled with insulation, doubled. For insulation, experts recommend using mineral wool. After that there is a layer of waterproofing. It is attached by means. Reiki are nailed perpendicular to the boards throughout the ceiling at an equal distance. They perform the functions of not only a waterproofing and thermal insulation fixer, but also ventilation.