COLUMN BUILDING SCIENCES performance exceeds the building code requirements for slabs by the International Energy Conservation Code (IECC) for Climate Zones 3 and 4-but is recommended by me.# Figure 3 shows both vertical and horizontal thermal insulation. This approach is recommended for International Energy Conservation Code (IECC) Climate Zones 5 and higher. The stem wall perimeter foundation can be insulated on the interior with extruded polystyrene (XPS) (Photo 1) or expanded polystyrene (EPS). Note the depth of the "seat" in the top of the stem wall to accommodate the thickness of the rigid insulation yet to be installed and the thickness of the slab yet to be cast. Horizontal insulation should be covered with a polyethylene vapor barrier (Photo 2). Note the vertical rigid insulation strip in the "seat" of the stem wall creating a thermal break between the yet to be cast slab and the support for the perimeter exterior wall framing. The stones on top of the polyethylene sheet are being used to keep the sheet poly from blowing away before the slab is cast. The concrete slab is then cast (Photo 3). Note that the protective membrane strip is yet to be installed. The protective membrane strip should bridge the top of the slab and the top of the stem wall. The protective membrane strip acts as a capillary break providing moisture control and acts as a termite and insect barrier. Figure 4 shows semirigid board insulation such as mineral wool/stone wool or fiberglass installed both horizontally and vertically. The key to Figure 4 is that PHOTO 1 Stem wall perimeter foundation insulated on the interior with extruded polystyrene (XPS). Note the depth of the "seat" in the top of the stem wall to accommodate the thickness of the rigid insulation yet to be installed and the thickness of the slab yet to be cast. FIGURE 3 Stem wall with horizontal and vertical insulation. Extruded polystyrene (XPS) or expanded polystyrene (EPS). Cladding Continuous Exterior Insulation Protective Membrane Strip Also Acts as Capillary Break and Acts as a Termite and Insect Barrier Rodent Protection for Continuous Rigid Insulation For Insect Protection Provide 3 ft of Mulch and Then Drought Resistent Plants Ground Slopes Away From Wall at 5% (6 in. per 10 ft) Cavity Insulation Gypsum Board Sealant, Adhesive or Gasket Sill Gasket Rigid Insulation as Bond Break Material Polyethylene Vapor Barrier Concrete Slab Rigid Board Insulation Extruded Polystyrene (XPS) or Expanded Polystyrene (EPS) Concrete Foundation Wall Granular Capillary Break and Drainage Pad (No Fines) Concrete Footing Below Frost Depth there must be an interior perimeter drain and a granular capillary break along the vertical portion-as well as the horizontal portion-of the mineral wool/stone wool or fiberglass layer. This is necessary to keep the PHOTO 2 Horizontal rigid insulation installed, covered with a polyethylene vapor barrier. Note the vertical rigid insulation strip in the "seat" of the stem wall creating a thermal break between the yet to be cast slab and the support for the perimeter exterior wall framing. The stones on top of the polyethylene sheet are being used to keep the sheet poly from blowing away before the slab is cast. PHOTO 3 Concrete slab is cast. Protective membrane strip is yet to installed. The protective membrane strip should bridge the top of the slab and the top of the stem wall. The protective membrane strip acts as a capillary break providing moisture control and acts as a termite and insect barrier. #The material cost of the insulation is low compared to the installation cost itself. IECC does not require slab insulation for Climate Zone 3, and I think that is a big mistake. Can't retrofit slab foundations easily. Why should you believe me? Ah, every time I have made a thermal resistance recommendation over the years I have pretty much ended up being wrong-I have consistently been too low. 78 ASHRAE JOURNAL ashrae.org M AY 2020https://www.ashrae.org/