ASHRAE Journal - March 2022 - 64

COLUMN BUILDING SCIENCES
So let's take a closer look at some of these
" hot rod " walls.
Single Top Plate
Vapor Control Layer as Per IRC
Fiberglass or Cellulose
Insulation in Stud Space
Figure 2:
Advanced Framing with Insulating Sheathing
Fiberglass batt, blown cellulose, sprayed
cellulose and sprayed fi berglass are
typically used to insulate the stud space.
Expanded polystyrene (EPS), extruded
polystyrene (XPS) and foil-faced polyisocyanurate
(PIR) board foam are used as the
exterior insulating sheathing. Spray foam
is used at the rim joist to control air leaks.
Fiberglass, blown and sprayed cellulose
are air permeable materials used in the
stud space of the wall, allowing possible
air paths between the interior and exterior
as well as convective looping in the insulation.
Dense pack cellulose has less air permeance,
but does not control air leakage.
Insulating sheathing (EPS, XPS and foilfaced
polyisocyanurate board foam (PIR)
products are air impermeable. When joints between
panels of insulation and the insulation and framing are
properly sealed with tape, mastic, caulk, etc., an effective
air control layer (air barrier system) can be created
at the exterior sheathing.
Rain control is typically addressed using a shingle
lapped and/or taped water control layer such as building
paper or a synthetic housewrap. It is possible to use
insulating sheathing as the water control layer if all the
intersections, windows, doors and other penetrations
are connected to the surface of the insulating sheathing
in a watertight manner, and the seams of the insulation
are taped or fl ashed to avoid water penetration.
Fiberglass or cellulose in the stud cavity are vapor permeable,
while EPS, XPS and PIR are moderately permeable,
moderately impermeable and completely impermeable,
respectively. Insulating sheathing reduces the
risk of winter condensation by increasing the temperature
of the condensing surface (condensation plane),
and reduces the risk of summer inward vapor drives by
slowing the vapor movement into the enclosure from
storage claddings such as masonry or stucco. The level
of vapor control in insulating sheathing walls is determined
in the International Residential Code (IRC).
(Yes, we were here before- " Hybrid Attics and Hybrid
64
ASHRAE JOURNAL ashrae.o rg M A R C H 2 0 2 2
2 × 6 Stud Wall at 24 in. o.c.
Taped and Painted 1/2 in. Gypsum
Wall Board as Interior Finish
Exterior Sheathing
Liquid-Applied Water
Control Layer
Drainage Gap/Channels/
Grooves Necessary Between
Drainage Plane and EPS
3 in. to 6 in. EPS Insulation
Glass Mesh Reinforced
Lamina and Synthetic
Stucco Finish
Insulation at
Rim Joist
Figure 3 Exterior Insulation Finish System (EIFS).
* 2 × 6 advanced wood-frame wall
* Glass faced gypsum sheathing
* Drainage gap/channels
* Stucco finish
* Fiberglass, cellulose or spray foam cavity insulation
* Liquid- or trowel-applied water control layer
* Exterior expanded polystyrene (EPS) insulation
Walls-Simple Physics, Complicated Language, " ASHRAE
Journal, October 2017).
Figure 3: Exterior Insulation Finish System (EIFS)
Fiberglass batt, blown cellulose, sprayed cellulose and
sprayed fi berglass are typically used to insulate the stud
space. Expanded polystyrene (EPS), extruded polystyrene
board foam is used as the exterior insulating
sheathing. Spray foam is used at the rim joist to control
air leaks.
Fiberglass, blown and sprayed cellulose are air permeable
materials used in the stud space of the wall, allowing
possible air paths between the interior and exterior
as well as convective looping in the insulation. Dense
pack cellulose has less air permeance but does not control
air leakage. The glass faced gypsum sheathing is air
permeable. When joints between the gypsum sheathing
are properly sealed with a liquid- or trowel- applied
water control layer, an effective air control layer (air barrier
system) is also created.
Rain control is typically addressed by providing a
drainage gap between the liquid- or trowel-applied
water control layer and the EPS sheathing.
Fiberglass or cellulose in the stud cavity are vapor permeable,
while EPS and the stucco lamina are moderately
http://ashrae.org
ASHRAE Journal - March 2022

Table of Contents for the Digital Edition of ASHRAE Journal - March 2022
