ASHRAE Journal - July 2020 - 62

COLUMN BUILDING SCIENCES

FIGURE 20 Concrete masonry unit (CMU) with exterior insulation and brick or stone veneer and vapor-impermeable/semi-permeable insulation.

Applicability
OK All hygrothermal regions.
OK All rain exposure zones.
OK All interior climate (Classes I, II and III).
Description This wall is an implementation of the "perfect wall," with all insulation outboard of the
structure, and a combined air/vapor/water control layer at the CMU surface, inboard of continuous
exterior insulation.
Drainage Cavity Hydrostatic pressure is controlled by providing a drainage space behind the
cladding. The ideal solution is to decouple the exterior brick veneer (a "reservoir" cladding) from the wall
assembly with a ventilated and drained cavity. The cavity behind the brick veneer should be at least 1 in.
(25 mm) wide and free from mortar droppings. It must also have air inlets ("weep holes") at its base and
air outlets ("weep holes") at its top to provide back ventilation of the brick veneer.
Exterior Insulation Vapor impermeable (foil-faced polyisocyanurate) or vapor semi-impermeable
(extruded polystyrene) acceptable.
Water Control Layer Combined air/vapor/water control layer at the exterior of CMU. Can be fully
adhered sheet membrane or trowel-on or spray-applied coating.
Air Control Layer Combined air/vapor/water control layer at the exterior of CMU.
Vapor Control Layer (Exterior) Combined air/vapor/water control layer at the exterior of CMU; vapor
impermeable.
Vapor Control Layer (Interior) and Condensation Control Interior latex paint (Class III) on
interior finishes. In cold climates, condensation is limited on the interior side of the air/water/vapor
control layer by installing all of the thermal insulation on the exterior side of these control layers. In
hot-humid climates, any moisture that condenses on the exterior side of the air/water control layer
will be drained to the exterior. This wall assembly will dry from the vapor control layer inward and will

dry from the vapor control layer outward.
Thermal Control Layer Continuous exterior rigid insulation.

FIGURE 21 Concrete masonry unit (CMU) with exterior insulation and brick or stone veneer and vapor-permeable insulation.

Applicability
OK All hygrothermal regions.
OK All rain exposure zones.
OK All interior climate (Classes I, II, and III).
Description This wall is an implementation of the "perfect wall," with all insulation outboard of the
structure, and a combined air/vapor/water control layer at the CMU surface, inboard of continuous
exterior insulation.
Drainage Cavity Hydrostatic pressure is controlled by providing a drainage space behind the cladding.
The ideal solution is to decouple the exterior brick veneer (a "reservoir" cladding) from the wall assembly
with a ventilated and drained cavity. The cavity behind the brick veneer should be at least 1 in. (25 mm)
wide and free from mortar droppings. It must also have air inlets ("weep holes") at its base and air
outlets ("weep holes") at its top to provide back ventilation of the brick veneer.
Exterior Insulation Vapor permeable (mineral wool or rigid fiberglass insulation) required.
Water Control Layer Combined air/vapor/water control layer at the exterior of CMU. Can be fully
adhered sheet membrane or trowel-on or spray-applied coating.
Air Control Layer Combined air/vapor/water control layer at the exterior of CMU.
Vapor Control Layer (Exterior) Combined air/vapor/water control layer at the exterior of CMU.
The vapor control layer can either be vapor impermeable or vapor permeable. Where the annual
average rainfall exceeds 20 in. (508 mm) and a reservoir cladding such as brick or stone veneer is
used, the vapor control layer should be vapor semipermeable (or less in permeance) to control inward
vapor drive.
Vapor Control Layer (Interior) and Condensation Control Interior latex paint (Class III) on interior
finishes. In cold climates, condensation is limited on the interior side of the air/water/vapor control
layer by installing all of the thermal insulation on the exterior side of these control layers. In hot-humid
climates, any moisture that condenses on the exterior side of the air/water control layer will be drained
to the exterior. This wall assembly will dry from the vapor control layer inward and will dry from the vapor
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control layer outward. If a vapor-permeable vapor control layer is used, coupled with mineral
wool insulation, through-wall vapor flow occurs. The wall assembly dries in both directions
depending on the moisture gradient.
Thermal Control Layer Continuous exterior rigid insulation.

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ASHRAE Journal - July 2020

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