Various types of insulation can be used, including rigid mineral fibre, extruded polystyrene, high-density expanded polystyrene, and closed cell spray foam.

It is important that the selected insulation product is moisture tolerant, as it will be exposed to dampness and possible wetting in this below-grade application.

The exterior insulation in this assembly will maintain the concrete slab at closer-to-indoor temperatures, enhancing comfort, typically reducing the risk of condensation and associated damage, and allowing for more durable installation of a wider range of floor finishes.

Although not always required by code, full insulation coverage below floor slabs is recommended. Compared to perimeter-insulated slabs, completely insulated slabs perform better in energy efficiency, moisture, and condensation control. They also result in a more occupant friendly, and thermally comfortable below-grade space.