ASHRAE Journal - August 2021 - 35

COLUMN BUILDING SCIENCES
Robust wildfi re resiliency involves
minimizing or eliminating roof ventilation,
minimizing drainage gaps
and back ventilation of claddings
and providing screens that resist
airborne ember/cinder entry. Fireresistant
claddings should be used.
Additionally, fi re-resistant continuous
exterior insulation should be
used or, alternatively, the combustible
continuous exterior insulation should
be protected.
FIGURE 5 Vented Roof Constructed From Non-Combustible Materials. Use rockwool 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 rockwool will depend on the ground snow load for the location.
Right off the bat, an ignition-resistant
or non-combustible cladding
should be coupled with a drainage
gap and water control layer to control
hydrostatic pressure.
The water control layer can take
numerous forms. It can be a mechanically
attached membrane, a fully
adhered membrane, a fl uid applied
coating, a sheet good with an integral
water control layer or rigid insulation
with sealed joints.
Figure 1 (page 33) shows a wall
assembly with an ignition-resistant
or non-combustible cladding, fi re
retardant or fi re resistant continuous
exterior insulation, fi re retardant
or fi re-resistant sheathing, fi re
retardant framing, fi re retardant or
fi re resistant cavity insulation and a
non-combustible interior lining such
as 5/8 inch (15.9 mm) " Type X " gypsum
board. The brick/stone veneer
is installed over a ¾ inch (19 mm)
drained and vented cavity. This cavity
should not be vented into soffi t
assemblies. It should be capped and
vented at the top to the exterior using
weep openings similar to the weep
openings typical at the bottom of the
wall. It is important not to provide
a pathway for airborne embers/cinders to enter soffi t
assemblies and ultimately roof assemblies. The 2021
International Wildland-Urban Interface Code (IWUIC)
expressly prohibits soffi t ventilation.
FIGURE 6 Vented vs. Unvented Attic With Vapor Diffusion Port. In the classic vented attic air change removes
water vapor from the attic. In an unvented attic with a vapor diffusion port water vapor is removed via vapor
diffusion rather than air change.
Figure 2 also shows a wall assembly with an ignitionresistant
or non-combustible cladding, fi re retardant or
fi re resistant continuous exterior insulation, fi re retardant
or fi re resistant sheathing, fi re retardant framing,
A U G U S T 2 0 2 1 ashrae.org ASHRAE JOURNAL
35
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ASHRAE Journal - August 2021

Table of Contents for the Digital Edition of ASHRAE Journal - August 2021

Contents
ASHRAE Journal - August 2021 - Intro
ASHRAE Journal - August 2021 - Cover1
ASHRAE Journal - August 2021 - Cover2
ASHRAE Journal - August 2021 - 1
ASHRAE Journal - August 2021 - Contents
ASHRAE Journal - August 2021 - 3
ASHRAE Journal - August 2021 - 4
ASHRAE Journal - August 2021 - 5
ASHRAE Journal - August 2021 - 6
ASHRAE Journal - August 2021 - 7
ASHRAE Journal - August 2021 - 8
ASHRAE Journal - August 2021 - 9
ASHRAE Journal - August 2021 - 10
ASHRAE Journal - August 2021 - 11
ASHRAE Journal - August 2021 - 12
ASHRAE Journal - August 2021 - 13
ASHRAE Journal - August 2021 - 14
ASHRAE Journal - August 2021 - 15
ASHRAE Journal - August 2021 - 16
ASHRAE Journal - August 2021 - 17
ASHRAE Journal - August 2021 - 18
ASHRAE Journal - August 2021 - 19
ASHRAE Journal - August 2021 - 20
ASHRAE Journal - August 2021 - 21
ASHRAE Journal - August 2021 - 22
ASHRAE Journal - August 2021 - 23
ASHRAE Journal - August 2021 - 24
ASHRAE Journal - August 2021 - 25
ASHRAE Journal - August 2021 - 26
ASHRAE Journal - August 2021 - 27
ASHRAE Journal - August 2021 - 28
ASHRAE Journal - August 2021 - 29
ASHRAE Journal - August 2021 - 30
ASHRAE Journal - August 2021 - 31
ASHRAE Journal - August 2021 - 32
ASHRAE Journal - August 2021 - 33
ASHRAE Journal - August 2021 - 34
ASHRAE Journal - August 2021 - 35
ASHRAE Journal - August 2021 - 36
ASHRAE Journal - August 2021 - 37
ASHRAE Journal - August 2021 - 38
ASHRAE Journal - August 2021 - 39
ASHRAE Journal - August 2021 - 40
ASHRAE Journal - August 2021 - 41
ASHRAE Journal - August 2021 - 42
ASHRAE Journal - August 2021 - 43
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ASHRAE Journal - August 2021 - Cover3
ASHRAE Journal - August 2021 - Cover4
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