ASHRAE Journal - May 2013 - 63

are all non-combustible. The sub-fascia wood is also fire
retardant treated wood. Note that these wood members
cannot be “beveled” as they will lose their fire properties.
A metal C-section is used as blocking to connect the outer
sub-facia to the inner sub-fascia. Note the continuous
soffit vent. A beautiful thing.
Could the rigid insulation under the fiber cement siding be rock wool as well? Sure. But it does not have to
be. Could the two layers of rigid insulation on the top of
the roof sheathing and under the rock wool also be rock
wool? Sure. But they do not have to be.
Could the cavity insulation in the in rafter space be
cellulose or fiberglass? Sure. Knock yourself out. How
about the wall cavity insulation? Same answer.
Could I construct Figure 1 as a conditioned unvented
attic assembly rather than a cathedral ceiling? Sure. Just
omit the gypsum board.
Ah, but what if I want to use spray polyurethane foam
in the rafter space? Check out Figure 2. One layer of rock
wool rigid board insulation provides the fire protection on
the top side of the structural roof deck. The spray polyurethane foam (SPF) handles the condensation control.
Note that in IECC Climate Zones 5 and higher the SPF
must be 2 lb/ft3 (32 kg/m3) density. The gypsum board
layer need not be installed if the assembly is an attic
space rather than a cathedral ceiling. However, in such
cases, an intumescent fireproofing coating applied to the
interior surface of the SPF will likely be necessary for fire
protection on the bottom side of the assembly.
Now let’s have some fun. Let’s take Figure 2 and rotate
it so that it is vertical and call it a wall. Modify it a bit
and we get Figure 3. Paperless exterior gypsum board (a

Figure 1: Vented Roof Constructed From Non-Combustible Materials.
Use rock wool insulation (aka “fluffy rocks”), fire retardant treated
plywood, fire retardant treated wood, metal roofing and fiber cement
siding, trim and soffit material (rocks in sheet form) and follow the applicable physics and you get something that handles the embers and the
ice dams. The metal “hat-channel” can be replaced with fire retardant
treated wood 2 × 4s lying “flat.” The structural geeks like the wood on
the flat better. The fire geeks like the metal better. Note that the density
of the rock wool will depend on the ground snow load for the location.

Figure 2: Non-Combustible Vented Roof With SPF. One layer of
rock wool rigid board insulation provides the fire protection on the
top side of the structural roof deck. The spray polyurethane foam
(SPF) handles the condensation control. Note that in IECC Climate
Zones 5 and higher the SPF must be 2 lb/ft3 (32 kg/m3) density.
Same comment as for Figure 1: the metal “hat-channel” can be
replaced with fire retardant treated wood 2 × 4s lying “flat.”
May 2013

Figure 3: My Gift to Chicago. Paperless exterior gypsum
board (a “sheet rock”; recall, that rocks don’t burn) is used as
an exterior sheathing to support a fully adhered membrane
(or a liquid applied membrane) water control, air control
layer and vapor control layer. Over these three control layers
goes the rock wool thermal control layer. Recall that “fluffy
rocks” don’t burn. A non-combustible fiber cement cladding is
attached through the rock wool thermal control layer using a
0.75 in. (19 mm) metal “hat-channel” furring/spacer strip. Yes,
this metal spacer can be replaced with fire retardant treated
wood furring. But check with the fire folks first.
ASHRAE Journal

63



ASHRAE Journal - May 2013

Table of Contents for the Digital Edition of ASHRAE Journal - May 2013

ASHRAE Journal - May 2013
Contents
Commentary
Industry News
Letters
Meetings and Shows
Feature Articles
VAV Reheat Versus Active Chilled Beams & DOAS
A Stable Whole Building Performance Method for Standard 90.1
Technology Award Case Studies:
PSU Design Build Project
Passive Cooling for School
Standing Columns
Building Sciences
InfoCenter
Refrigeration Applications
IAQ Applications
Engineer's Notebook
Products
Data Centers
Emerging Technologies
Classified Advertising
Advertisers Index
ASHRAE Journal - May 2013 - ASHRAE Journal - May 2013
ASHRAE Journal - May 2013 - Cover2
ASHRAE Journal - May 2013 - 1
ASHRAE Journal - May 2013 - 2
ASHRAE Journal - May 2013 - Contents
ASHRAE Journal - May 2013 - Commentary
ASHRAE Journal - May 2013 - 5
ASHRAE Journal - May 2013 - Industry News
ASHRAE Journal - May 2013 - 7
ASHRAE Journal - May 2013 - 8
ASHRAE Journal - May 2013 - 9
ASHRAE Journal - May 2013 - 10
ASHRAE Journal - May 2013 - 11
ASHRAE Journal - May 2013 - 12
ASHRAE Journal - May 2013 - 13
ASHRAE Journal - May 2013 - Letters
ASHRAE Journal - May 2013 - 15
ASHRAE Journal - May 2013 - Meetings and Shows
ASHRAE Journal - May 2013 - 17
ASHRAE Journal - May 2013 - VAV Reheat Versus Active Chilled Beams & DOAS
ASHRAE Journal - May 2013 - 19
ASHRAE Journal - May 2013 - 20
ASHRAE Journal - May 2013 - 21
ASHRAE Journal - May 2013 - 22
ASHRAE Journal - May 2013 - 23
ASHRAE Journal - May 2013 - 24
ASHRAE Journal - May 2013 - 25
ASHRAE Journal - May 2013 - 26
ASHRAE Journal - May 2013 - 27
ASHRAE Journal - May 2013 - 28
ASHRAE Journal - May 2013 - 29
ASHRAE Journal - May 2013 - 30
ASHRAE Journal - May 2013 - 31
ASHRAE Journal - May 2013 - 32
ASHRAE Journal - May 2013 - A Stable Whole Building Performance Method for Standard 90.1
ASHRAE Journal - May 2013 - 34
ASHRAE Journal - May 2013 - 35
ASHRAE Journal - May 2013 - 36
ASHRAE Journal - May 2013 - 37
ASHRAE Journal - May 2013 - 38
ASHRAE Journal - May 2013 - 39
ASHRAE Journal - May 2013 - 40
ASHRAE Journal - May 2013 - 41
ASHRAE Journal - May 2013 - 42
ASHRAE Journal - May 2013 - 43
ASHRAE Journal - May 2013 - 44
ASHRAE Journal - May 2013 - 45
ASHRAE Journal - May 2013 - PSU Design Build Project
ASHRAE Journal - May 2013 - 47
ASHRAE Journal - May 2013 - 48
ASHRAE Journal - May 2013 - 49
ASHRAE Journal - May 2013 - 50
ASHRAE Journal - May 2013 - 51
ASHRAE Journal - May 2013 - 52
ASHRAE Journal - May 2013 - 53
ASHRAE Journal - May 2013 - Passive Cooling for School
ASHRAE Journal - May 2013 - 55
ASHRAE Journal - May 2013 - 56
ASHRAE Journal - May 2013 - 57
ASHRAE Journal - May 2013 - 58
ASHRAE Journal - May 2013 - 59
ASHRAE Journal - May 2013 - 60
ASHRAE Journal - May 2013 - 61
ASHRAE Journal - May 2013 - Building Sciences
ASHRAE Journal - May 2013 - 63
ASHRAE Journal - May 2013 - 64
ASHRAE Journal - May 2013 - 65
ASHRAE Journal - May 2013 - 66
ASHRAE Journal - May 2013 - 67
ASHRAE Journal - May 2013 - 68
ASHRAE Journal - May 2013 - 69
ASHRAE Journal - May 2013 - InfoCenter
ASHRAE Journal - May 2013 - 71
ASHRAE Journal - May 2013 - 72
ASHRAE Journal - May 2013 - 73
ASHRAE Journal - May 2013 - 74
ASHRAE Journal - May 2013 - Refrigeration Applications
ASHRAE Journal - May 2013 - 76
ASHRAE Journal - May 2013 - 77
ASHRAE Journal - May 2013 - IAQ Applications
ASHRAE Journal - May 2013 - 79
ASHRAE Journal - May 2013 - 80
ASHRAE Journal - May 2013 - 81
ASHRAE Journal - May 2013 - 82
ASHRAE Journal - May 2013 - 83
ASHRAE Journal - May 2013 - Engineer's Notebook
ASHRAE Journal - May 2013 - 85
ASHRAE Journal - May 2013 - Products
ASHRAE Journal - May 2013 - 87
ASHRAE Journal - May 2013 - Data Centers
ASHRAE Journal - May 2013 - 89
ASHRAE Journal - May 2013 - 90
ASHRAE Journal - May 2013 - 91
ASHRAE Journal - May 2013 - Emerging Technologies
ASHRAE Journal - May 2013 - 93
ASHRAE Journal - May 2013 - 94
ASHRAE Journal - May 2013 - Classified Advertising
ASHRAE Journal - May 2013 - Advertisers Index
ASHRAE Journal - May 2013 - Cover3
ASHRAE Journal - May 2013 - Cover4
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