Thermal Air Flow

• If the space under the suspended slab is part of the home's thermal envelop, use the minimum insulation required by the building codes for your area. Blocking air flow under a ground level floating floor can limit cooling abilities during hot months.
  
  

Under Slab Insulation

• Polystyrene boards or foil faced polystyrene boards should be installed on the underside of a suspended concrete slab. The boards are typically installed with special retaining pins that have expanding plug ends. The pins allow the needed still air space to exist between the insulating boards and the concrete slab. This type of insulation is sufficient for codes in most areas.
  
  

Top Side Insulation

• Suspended slabs of cast in-situ concrete are initially ground bearing, but are built to be suspended slabs once the fill under them has settled. In this situation, insulation has to be placed on top of the suspended concrete slab. Polystyrene boards are available in a wide variety of load bearing thicknesses. Insulating boards are placed directly on top of the slab. Additional flooring materials, such as plywood, are then installed on top of the polystyrene boards. The floor can be finished with the desired materials, such as tile, carpet or wood.