When considering the thermal performance of encased structural steelwork, it's often the case that the steelwork itself is a significant contributor to thermal bridging through the overall construction. Promat recommend providing a boarded encasement system using one of our three fire protection boards suitable for use in this application: PROMATECT®-XW, PROMATECT®-250 or VERMICULUX®-S, then to fill all voids and air spaces within the steelwork encasements with a low density glass wool insulation, in the density range of 10 to 30kg/m³.

Stone or rock wool type non-combustible insulation products are not recommended for increasing the thermal performance within the steelwork encasements. This type of insulation can act as a heat sink, potentially causing hot spots within the overall detail which could go above the required limiting steel temperature. Low density glass wool insulation will tend to melt during a fire, whilst still being contained within the encasement, without compromising the stated fire performance of the steelwork protection.

The use of any kind of rigid thermoset plastic type insulation is not supported or endorsed in any way by Promat, in any passive fire protection systems, due to the toxic nature of the smoke and gases emitted by this type of insulation in a fire.