The table lists the minimum thickness of thermal insulation for a flat roof according to the current thermal protection requirements for buildings. A Ceram rib-and-slab ceiling was adopted for the structural layer of the double-section roof, reinforced concrete slab and a wooden beam ceiling with a soffit. The types of ceilings selected for the analysis occur in newly erected buildings, as well as in insulated buildings. Rigid insulation boards can be used to insulate flat roofs, insulating mats and backfill materials. In the case of double non-passable flat roofs, it is particularly advantageous to use backfill materials to insulate the attic space., where they are placed directly on the ceiling, creating a layer of the required thickness. When used on non-flammable light ceilings, loose, backfill materials, like for example.: wood shavings and sawdust mineralized with lime or granulated mineral wool, there is a possibility of blowing them out during intensive air movement in the ventilated space. For this reason, the layer of thermal insulation material must be secured from above with a thin plastic mesh. The selected calculation results are presented in tab, which summarizes the minimum thickness of the roof insulation required according to the specific types of ceilings and thermal insulation materials. In the table, the values ​​of the thermal resistance of the ceilings for individual types of ceilings were calculated together with the ceiling made of cement-lime plaster with a thickness of 1,5 cm, in the case of a flat roof with an inaccessible attic space. In flat roofs, in which the high attic space is used by users as a warehouse or drying room, there is a need to lay a floor layer on the thermal insulation layer of the ceiling (floors). Due to the function of the attic, only load-bearing materials may be used under the floor for thermal insulation, suitably hard, thermal insulation boards made of mineral wool, polyurethane, e.t.c.

For attic ceilings, the required ceiling insulation thicknesses are required for ceilings made of cement-lime plaster with a thickness of 1.5 cm and a chipboard concrete floor, thick 4 cm, compiled in tab.

Minimum thickness of thermal insulation d [cm] acc. to a two-section flat roof

attention: Physical properties for thermal insulation materials were adopted according to [35] for moderately humid conditions.

In the table, the minimum thickness of thermal insulation is the greatest for the "coldest" ceiling, tj. monolithic slab ceiling (second column of table). However, these thicknesses differ little, within 2-4 cm from the required thickness of thermal insulation for the "warmest" ceiling, tj. a wooden beam ceiling with a soffit (third column of tab.). It can be stated, that the type of floor structure has little effect on the minimal, required, thickness of the insulation layer. Therefore, generally, in the case of thermal insulation in the form of polystyrene or mineral wool boards, the minimum thickness of insulation for double-section flat roofs, regardless of the structure of the ceilings, is approximately 15 cm. However, for loose materials, such as e.g.. mineralized sawdust or wood shavings, the minimum thickness is from 25 to approx 30 cm.

It should be remembered that the thermal insulation material located on the ceiling is inaccessible (non-manhole) of the flat roof is exposed to destruction and destruction by birds and rodents nesting in it. Therefore, in addition to securing the thermal insulation against blowing out, proper meshing of the air inlet and outlet openings to the flat roof space should be used..