ASHRAE Journal - August 2021 - 32

BUILDING SCIENCES
COLUMN
Joseph W. Lstiburek
Wildfires
BY JOSEPH W. LSTIBUREK, PH.D., P.ENG., FELLOW ASHRAE
In general there are two main types of fire issues: fires emanating from the interior of
a building and fires emanating from the exterior of a building, such as wildfires.
The single most important design considerations for
fire safety relating to interior fires is discovery of the
fire and getting everyone out of the home quickly and
safely. Smoke detectors, carbon monoxide detectors and
egress are central to this approach. This is a huge, huge,
big deal. It is obvious and we are not going to address it
here.
The single most important design considerations for
fire safety relating to exterior fires is the prevention
of the spread of fire by vegetation to a building ( " wildfires " )
and the spread of fire from the exterior of one
structure to another. Again this is a huge, huge, big deal
and obvious and we are going to focus on it, particularly
focusing on the wildfire.*
With respect to wildfires, the issue is burning embers.
Roofs are particularly vulnerable to burning embers-
both from the perspective of the roof covering and from
the perspective of roof venting. If we could build roofs
that are not vented in wildfire areas we would all be
better off. We are going to cover this, but there are still
places where we have to vent because we do not have a
*This has nothing to do with a pony or Nebraska. Michael
Martin Murphy had a hit song in 1975 titled " Wildfire " about a
pony named Wildfire lost in a blizzard in Nebraska, a favorite of
David Letterman and Paul Shaffer for reasons that are " haunting
and disturbingly mysterious, " much like the fire performance
of walls and roofs during wildfire events.
32
ASHRAE JOURNAL ashrae.org A U G UST 2021
better way of dealing with the " confounding issue " even
though we are in a wildfire risk area. More on that later.
We also have to deal with burning embers and walls,
particularly walls with vented claddings. Again, more on
that later. Seems to me that this venting thing can be a
fire thing. Just ask the Brits (we were here before: " Great
Fire of London, " ASHRAE Journal, July 2017).
Homes built in regions designated as Urban Wildland
Interface Zones are at a high risk for fire exposure.
Wildfires burn with speed and intensity that often leads
to a high percentage of homes lost in these communities.
However, the ignition of homes is typically not
caused directly by flames but rather by ignited embers
becoming airborne.
A bit of obvious things homeowners can address,
particularly with respect to roofs and walls: for there
to be a wildfire problem you need a fuel source. Some
obvious fuel sources are within the control of homeowners:
leaves, pine needles, ground debris, trash, grasses
and shrubs. Burning embers generated from these fuel
sources are transported through the air and become
deposited on roofs of homes or can be drawn into
the attic through the openings in roof vents. Embers
deposited on roofs may ignite debris on rooftops and in
Joseph W. Lstiburek, Ph.D., P.Eng., is a principal of Building Science Corporation in
Westford, Mass. Visit www.buildingscience.com.
http://www.buildingscience.com http://www.ashrae.org

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
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ASHRAE Journal - August 2021 - 25
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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
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ASHRAE Journal - August 2021 - Cover3
ASHRAE Journal - August 2021 - Cover4
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