The flat roof protects the internal rooms of the building against rainfall and temperature changes, that is, the influence of the external climate. The flat roof consists of many layers with different functions. On the supporting structure (ceiling) there is often a vapor barrier (vapor barrier), then a thermal insulation layer (thermal insulation). Between the roofing material (waterproof layer) and the thermal insulation in ventilated flat roofs is an air space connected with the outside air through intake and exhaust openings.

Double roofs have a ventilated air space between the insulated ceiling and the roof covering structure. They are divided into flat roofs with a man-pass attic and flat roofs with a non-manhole attic..

Slotted roofs are structures, in which over the insulating layer, placed on the supporting structure, there are air gaps under the roofing, most often several centimeters, combined with the outside air.

Solid roofs have all the construction layers completely adjacent to each other, tj. on the supporting structure of the ceilings (covers) are arranged directly: insulating layer and cover. Usually, under the insulating layer in solid flat roofs, there is a vapor barrier.
Ventilated flat roofs differ from full flat roofs in this respect, that under the covering layer there is a venting layer in the form of small channels created by the use of special roofing felt with coarse grains or perforated roofing felt.