High-R20 Concrete Foundation Construction Diagram – Building Science

This construction strategy has an installed insulation R-value of R-20.

Source: www.buildingscience.com        >” […]


  • Dampproofing
  • 2″ XPS rigid insulation
  • Concrete foundation wall
  • 2″ XPS rigid insulation
  • 2″ XPS rigid sub-slab insulation
  • Gypsum board with vapor retarder paint
  • 2″ XPS rigid insulation under slab

Thermal Control:  This construction strategy has an installed insulation R-value of R-20 and has a predicted annual heating energy loss of 16.7 MBtus.

Moisture Control:  Two inches of XPS on the interior, connected to the thermal break at the slab edge, controls the interior vapor drive and capillary wicking to the interior so there are no moisture related issues from inward vapor diffusion or capillary wicking.

Constructability and Cost:  The interior of the insulated concrete form will require drywall or other thermal barrier to achieve the fire rating required by code. The gypsum board is very easy to attach to the plastic clips designed into the ICF. The drywall should not be painted, if it is not necessary, to allow maximum drying of the concrete. It may be easier and more practical to install a thin framed wall (e.g. 2×3 wood or steel framing) on the interior of the ICF to allow any necessary services to be run in the wall, and potentially more insulation.

Other Considerations:  Because the concrete is installed between two vapor retarding layers, it will take several years for the concrete to dry to equilibrium. Since additional interior vapor control should be avoided, no more than latex paint should be used on the interior surface of the drywall. […]”<


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