ASHRAE Journal - May 2021 - 51

COLUMN BUILDING SCIENCES

FIGURE 2 Gutters and Downspouts. Direct rainwater from gutters and downspouts
away from buildings.

Rainwater Falling on Roof is
Collected in Gutters

FIGURE 4 Pea Gravel-Crushed Stone Perimeter Pest-Resistant Ground Break
(Basement Foundation). The thickness of the pea gravel-crushed stone layer should
be a minimum of 4 in. (102 mm). The pea gravel-crushed stone ground break
should slope away from the building at approximately 5% (½ in./ft [0.04 mm/m]).

Gypsum Board With Semipermeable (Latex Paint)

Vinyl Siding
Overhang Protects the
Ground Around the
Foundation from Getting
Saturated

Sealant, Adhesive or
Gasket
Adhesive
Sealant, Adhesive
Or Gasket
Plastic L-Bracket for
Insect/Rodent Protection
Of Rigid Insulation
For Pest Protection Provide
2 ft of Pea Gravel
Or Crushed Stone 4 in. Thick

Downspouts Carry
Rainwater From the Roof
Away From the Foundation

Ground Slopes Away
From the Foundation

Ground Slopes Away From
Wall at 5% (6 in. per 10 ft)

FIGURE 3 Pea Gravel-Crushed Stone Perimeter Pest-Resistant Ground Break (Slab
Foundation). The thickness of the pea gravel-crushed stone layer should be a
minimum of 4 in. (102 mm). The pea gravel-crushed stone ground break should
slope away from the building at approximately 5% (½ in./ft [0.04 mm/m]).

Cladding
Continuous Exterior Insulation
Fully Adhered Membrane or Fluid
Applied or Integral Water Control
Layer, Air Control Layer
Structural Sheathing
Rodent Protection for
Continuous Rigid Insulation
Protection Board or Panel

Cavity Insulation
Gypsum Board
Flashing Set in Mastic and
Sealed to Slab
Sealant, Adhesive or Gasket
Sill Gasket
Reinforced Structural
Concrete Slab

For Pest Protection Provide 2 ft of Pea
Gravel or Crushed Stone 4 in. Thick
Granular Capillary
Break and Drainage
Pad (No Fines)
Ground Slopes Away From
Wall at 5% (6 in. per 10 ft)

Concrete Stem Wall

Rigid Insulation
Polyethylene Vapor Barrier
Extended Under Stem Wall Where
It Also Acts as a Capillary Break

and clutter should not be stored near buildings.
Provide 2 ft (0.6 m) of pea gravel or crushed stone and
then plant drought-resistant plants and do not overirrigate. Alternative pest-resistant ground breaks such
as graded basalt particles, concrete skirts or concrete
pavers are also effective.

Impermeable Backﬁll
Free-Draining Backﬁll
Dampprooﬁng
Filter Fabric

Sealant, Adhesive or Gasket
Sealant at Corner of Bottom Plate and
Subﬂoor or Gasket Under Bottom Plate
Sealant Cavity Insulation
Sealant, Adhesive or Gasket
Sill Gasket (Also Acts as Capillary Break)
Concrete Foundation Wall
Unfaced Extruded or Expanded Polystyrene
Rigid Insulation (Vapor Semipermeable
With Taped or Sealed Joints)
Gypsum Board Over Furring Strips
Gypsum Board Thermal Barrier Necessary
When Rigid Insulation is Not Rated for
Exposed Application
Sealant
Gypsum Board Held Up From Slab
Concrete Slab
Extruded Polystyrene, Expanded Polystyrene or
High-Density Mineral Wool

Stone Drainage Bed
Perforated
Drain Pipe
Capillary Break Over Footing
(Dampprooﬁng or Membrane)

Concrete Footing
Drain Pipe Through Footing

Sub-Slab Stone
Layer (No Fines)

Figure 3 and Figure 4 as well as Photo 1 and Photo 2 illustrate the use of a 2 ft (0.6 m) wide perimeter pest-resistant pea gravel-crushed stone ground break. The thickness of the pea gravel-crushed stone layer should be a
minimum of 4 in. (102 mm). The pea gravel-crushed
stone ground break should slope away from the building
at approximately 5% (½ in./ft [0.04 mm/m]).
Photo 3 and Photo 4 illustrate the use of a 2 ft (0.6 m)
wide perimeter concrete skirt ground break. Its thickness should be a minimum of 4 in. (102 mm). The
concrete should be cast on a 4 in. (102 mm) thick stone
capillary break. Control joints should be provided every
4 ft (1.2 m). In Climate Zones 5 and higher, the concrete should be air entrained to a minimum of 5% at
compressive strength of 3,500 psi (24 132 kPa) to resist
freeze-thaw damage. The concrete skirt ground break
should slope away from the building at approximately
5% (½ in./ft [0.04 mm/m]).
Photo 5 illustrates the use of a 2 ft (0.6 m) wide
M AY 2021

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