ASHRAE Journal - March 2022 - 63

COLUMN BUILDING SCIENCES
end I get a " nominal " R-27, and
at the high end I get a " nominal "
R-47. Getting serious insulation
" horsepower " now.
Let's go to multiple layers
Base Assembly
Rigid Insulation
Multiple Layers
Rigid Insulation + Furring
Truss Wall/Offset
Double Wall
(also Figure 1). How about 4 in.
(102 mm)-two 2 in. (51 mm)
layers with 1 × 4 furring strips to
handle the cladding attachment.
Okay, we now get to add an additional
R-15 to R-30 depending on
the insulation selection. Wow.
At the low end, I get a " nominal "
R-35, and at the high end I
get a " nominal " R-65. You want
more than 4 in. ((102 mm)? Go
for it. Easy to do 6 in. (152 mm)
or 8 in. (203 mm). Yes, we were
here before ( " Leiningen vs. the
Ants Redux, " ASHRAE Journal,
October 2011). Yup, you could do
8 in. (203 mm) on a 2 × 6 wall-
approximately 14 in. (356 mm) total.§
Yup, I see it coming, that train coming
down the track. What if I don't want or like
spray polyurethane foam (SPF) or any of
the rigid insulations? Relax. We can do all
of this with cellulose or fi berglass or Gloria
Vanderbilt's ground up blue jeans as cavity
insulation. Use a " truss wall/offset " or go
to a " double wall " (yes, also Figure 1). You
want R-60 with cellulose? Easy. You need
approximately 16 in. (406 mm) of insulation.
You get 5.5 in. (140 mm) (R-20) in the
base assembly. Add a " wall truss " that is 11
in. (279 mm) thick, and you get approximately
R-40 more. You don't like a " wall
truss " ? Add a second wall to the outside-
go to a " double wall. " Heck, you want more
than R-60? Go for it. Easy to get to R-70 or
R-80.#
Fiberglass
Cellulose
SPF Fiberglass
Cellulose
EPS
SPF Fiberglass
Cellulose
XPS
FoilFaced
Polyisocyanurate
Stone
Wool
EPS
XPS
FoilFaced
Stone
Wool
Polyisocyanurate
FIGURE
1 Turbocharged Advanced Frame Walls. Start with a 2 × 6 advanced frame wall as the " base assembly " and add
the " horsepower " -exterior continuous insulation, truss wall/offset and double wall.
Single Top Plate
2 × 6 Stud Wall at 24 in. o.c.
Taped and Painted 1/2 in. Gypsum
Wall Board as Interior Finish
Sheathing; 1 in. to 4 in. Typical
Fiberglass or Cellulose
Insulation in Stud Space
XPS Insulating Exterior
Cladding
Furring Strips
Tape Joints in XPS
Sheathing
Fiberglass Cellulose
Fiberglass Cellulose
SPF
Fiberglass Cellulose
Fiberglass Cellulose
Spray Foam
Insulation at
Rim Joist
FIGURE 2 Advanced Framing with Insulating Sheathing.
* 2 × 6 advanced wood-frame wall
* Extruded polystyrene (XPS) insulating sheathing
* Fiberglass, cellulose or spray foam cavity insulation
* Drainage space, creating a minimum 1/4 in. (6.4 mm)
ventilation gap/drainage gap behind cladding
§If it was me-note the " me " part-I would go with the closed-cell spray foam (R-35) and 6 in. (152 mm) of foil-faced polyisocyanurate
(R-40), giving me a nominal R-75-the 12 in. (305 mm) total in my version of the song.
#Note that I am avoiding the question of whether this level of thermal resistance makes sense. Further note that I have an 800 horsepower
car. The reasons for why I have that much horsepower in a car are varied and have led to therapy. Further note I love hot rods and
they make perfect sense to me even though they make no sense to many other folks. Other folks want R-70 walls-and they want them
out of " carbon neutral " stuff. I get it.
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ASHRAE Journal - March 2022

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