ASHRAE Journal - March 2021 - 53

COLUMN BUILDING SCIENCES

interior vapor control layer should be located within the
frame wall, thereby permitting inward drying.
All interior concrete surfaces are wrapped with the
spray foam insulation layer-particularly at the top of the
wall and at foundation " step downs. " Note the spray foam
insulation applied at the rim joist assembly. Note the capillary break at the top of the footing. Further note the air
sealing of the spray foam insulation connecting the concrete ﬂoor slab to the perimeter concrete foundation wall.

Concrete Basement Foundation With Interior Rigid
Insulation and an Interior Insulated Frame Wall
Applicability-All Hygro-Thermal Regions

FIGURE 3 Concrete basement foundation with interior spray polyurethane foam
insulation.

High Density Spray Foam
Sealant
Water Control Layer
Capillary Break
High Density Spray Foam
Steel Stud Assembly
Dampprooﬁng

Concrete Foundation Wall
Gypsum Board
Bond Break
Sill Seal Thermal Break and Capillary Break
Concrete Slab

Filter Fabric

Figure 4 illustrates a concrete basement foundation
Coarse Gravel
(No Fines)
wall with interior rigid insulation and an interior insulated frame wall. The key to this assembly is the use of
Perforated
non-water-sensitive rigid insulation on the interior
Drain Pipe
that still permits drying to the interior. The recomPolyethylene Vapor Barrier
Capillary Break Over
mended permeance of the interior rigid insulation
Footing (Dampprooﬁng or Concrete
Granular Capillary Break and
Footing
layer is approximately 1 perm. This typically limits
Membrane)
Drainage Pad (No Fines)
the thermal resistance of the interior
FIGURE 4 Concrete basement foundation wall with interior rigid insulation and an interior insulated frame wall.
rigid insulation layer, and an insulated
Wood Siding (All
Cavity Insulation
frame wall assembly can be located to the
Surfaces Coated)
Gypsum Board
Rigid Insulation (Taped
interior of the interior rigid insulation
Or Sealed Joints)
Sealant, Adhesive or Gasket
(Photo 3). No interior vapor control layer
Air Space
Sealant at Corner of Bottom Plate and Subﬂoor or
is located within the frame wall, thereby Sealant, Adhesive or Gasket
Gasket Under Bottom Plate
permitting inward drying.
Cavity Insulation
Adhesive
All interior concrete surfaces are
Sealant
Furring
Wood Filler (Draftstop)
wrapped with the rigid insulation layer-
Sealant, Adhesive or Gasket
particularly at the top of the wall and at
Sealant, Adhesive or Gasket
foundation " step downs. " Exterior rigid
Sill Gasket
Ground Slopes Away From
Treated Wood Frame Wall
insulation is located at the rim joist ﬂoor
Wall at 5% (6 in. per 10 ft)
Gypsum Board With Vapor Semipermeable (Latex) Paint
Impermeable Backﬁll
framing to control summer condensation.
Unfaced Batt Insulation
When insulating sheathing is not used,
Impermeable Backﬁll
Concrete Foundation Wall
rigid insulation should be installed to the
Granular Backﬁll
Extruded or Expanded Polystyrene Rigid
Insulation (Taped or Sealed Joints)
interior of the rim joist or an air impermeTreated Wood Bottom Plate
able insulation should be applied at the
Dampprooﬁng
Sealant, Adhesive or Gasket
rim joist assembly. Note the capillary break
Sealant
Sealant or Gasket Under Bottom Plate
at the top of the footing. Further note the
Filter Fabric
Concrete Slab
air sealing of the rigid insulation at the top
Expanded Polystyrene Rigid Insulation
of the concrete ﬂoor slab-a sealant is used
Coarse Gravel
or High Density Mineral Fiberboard
(No Fines)
to seal the top of the concrete slab to the
rigid insulation, and an additional sealant
Perforated
Granular Capillary Break and
Drain Pipe
is used to seal the rigid insulation to the
Drainage Pad (No Fines)
interior of the concrete perimeter foundaCapillary Break Over Footing
Extruded Polystyrene Rigid Insulation as Bond Break
(Dampprooﬁng or Membrane)
tion wall. These two seals are necessary to
Concrete Footing
control soil gas ingress.
MARCH 2021

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ASHRAE Journal - March 2021

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