In the buildings industry, the meaning of “green” has evolved significantly. In the 1980s the term focused tightly on environmental impacts. Since then it has broad- ened to include concepts of sus- tainability and then of resilience.
The Resilient Design Institute (
resil-ientdesign.org) identifies resilience as
“the capacity to adapt to changing conditions and to maintain or regain functional-ity and vitality in the face of distress or
disturbance.” This approach encompasses
environmental as well as economic and
Resilience goes beyond durability to
redundancy and back-ups. It focuses on
extreme weather as well as power outages and transportation interruptions. It
encompasses safety and comfort for occupants and production of power, lighting
New construction in North America
accounts for roughly 0.5 billion square
feet of roofing installed each year.
Existing buildings account for 2.5 billion square feet of replacement roofing.
The combined volumes are a significant
opportunity for the resilient approach.
No other major building system is
installed as frequently or offers as much
potential for resilience.
When you consider the view of an
urban landscape from an airplane, you see
an expanse of roofs. Outside the urban
core of high rises, you see vast numbers of
low commercial buildings – offices, apartments, and big box retail – with large
roof areas. The roof area of many of these
buildings exceeds the area of their outside
walls. Roofs are critical membranes that
interact with the outside environment
and affect the interior environment.
In the pursuit of resilience, nine strate-
gies can be applied to roofing. Some of
these strategies are familiar, some are
emerging, but all can work together.
Durable materials make a roof
last longer and slow the flow
of used materials to landfills.
Durability depends on a system’s
total thickness and its thickness over
reinforcement. Other important factors
are tensile and breaking strength, hail
ratings, and heat and UV aging.
The roof membrane also benefits from
protection above and below. Mats and
walkways protect the roof’s surface while
cover boards provide reinforcement
Redundant design provides
more reinforcement for durable
materials. Critical roof areas
receive sacrificial layers or multi-
ple plies in base sheet/cap sheet combina-
tions. Wider seams, greater flashing heights
and multiple flashings add redundancy.
The attachment method can also be
redundant in its density and by accommodating critical areas like perimeters.
Non-penetrating fasteners, fully adhered
methods and induction-welded systems
increase durability. Factory-assembled
membranes and curb flashings can provide
Wind resistance is increased
by paying special attention to
attachments, especially roof
BY JIM HOFF
Resilient approaches minimize environmental impact
while maximizing return on roof investment
Roles in Resilience