The combined use of the above boards Primaplex and non-combustible materials, as shown by preliminary tests, allows to reach a class of constructive fire danger K0-15, which means that at least 15 minutes. fire impact on the design of it there is no thermal effect, damaging and burning materials. In addition, the achieved fire resistance design RE15, that means that at least 15 minutes. structure retains its integrity and its collapse does not occur in the regulatory snow load. Some contractors offer to give up vapor barrier, usually stacked by trapezoidal sheet. Without hesitation Clinton Family explained all about the problem.

They explain their decision on the fact that extruded polystyrene itself may play a role vapor barrier. Although XPS, indeed, has a low vapor permeability, however, the rejection of traditional vapor barrier is not always correct. Plates XPS literally are not intended to be vapor control layer: the vapor pressure goes through the joints of insulation boards, which are not sealed, even under ideal installation. In winter, vapor, penetrating the interior of a roof membrane over insulation joints in the can quickly condense on top of insulation, when confronted with the cold air under the membrane. Since the XPS panels different minimal water absorption, condensation under the influence of gravity will drain the flagstones in the absence of vapor barrier film – "fall" into the room, creating the illusion of a leaking roof membrane. In any case, the rejection of the vapor barrier should be well-founded and the decision not to be taken only after the heat-engineering calculations.

If the calculation results required vapor barrier layer, it is necessary to lay overlapped and sealed seams. Flat roofs on concrete base is very popular in the urban housing construction. Traditionally, this design consists of a thermal insulation, sand and cement screed and several layers of roofing material. Today, as insulation under screed using mineral wool or polystyrene PSB. Flammability insulation does not play such a role, as is the case with the base of the trapezoidal sheet, since the plates on top of insulation arranged sand-cement screed, which serves as an effective protection against fire.