This below-grade slab assembly consists of rigid insulation placed beneath the polyethylene air barrier and concrete slab. High effective R-values are achieved by using continuous insulation outside of the concrete slab.

The insulation product used in this arrangement should be highly moisture tolerant and suitable for below-grade applications.

In cold climates, insulation placed on the exterior of the slab increases the temperature of the concrete and consequently often reduces the risk of condensation and associated damage to moisture-sensitive interior floor components and finishes.

A capillary break is provided between the slab assembly and the ground by a layer of course, clean granular fill to eliminate hydrostatic pressure on the floor assembly and reduce the risk of water ingress. The polyethylene also functions as a capillary break in this assembly.