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Roofs, Energy Efficiency, Codes and Sustainability: Complexity and Compromise on the Road to Net Zero

May 15, 2011

ROOFS, ENERGY EFFICIENCY, CODES, AND SUSTAINABILITY:
COMPLEXITY AND COMPROMISE ON THE ROAD TO NET ZERO
BY R. CHRISTOPHER MATHIS
MATHIS CONSULTING COMPANY
2002 Riverside Drive, Suite 42F, Asheville, NC 28814
P: 828-273-0696 • F: 828-254-5455 • E-mail: chris@mathisconsulting.com
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ABSTRACT
Over the past few years, energy codes have evolved to more highly prioritize building
envelopes, especially their energy efficiency and the durability of that delivered efficiency.
Unfortunately, the processes by which codes and standards are developed can result in a
chaotic landscape of requirements – prescriptive provisions, performance-based provisions,
requirements that differ from one code to another, and even requirements that seem internally
inconsistent within the same code. This paper seeks to quantify the diversity of
requirements currently in the marketplace governing commercial roof insulation and to
assist building industry professionals involved in roofing to better understand and navigate
this chaotic and changing regulatory landscape.
SPEAKER
R. CHRISTOPHER MATHIS — MATHIS CONSULTING COMPANY
R. CHRISTOPHER (“CHRIS”) MATHIS is a building scientist who has spent the past 30
years focusing on how buildings and building products perform – from energy efficiency to
code compliance to long-term durability and sustainability. Chris holds a master’s degree in
architectural science from MIT, where his graduate work focused on energy use in buildings
He is an active participant in national codes and standards development, having served four
times on the ICC’s Energy Code Development Committee and currently serving on the drafting
committee for the new International Green Construction Code. He served on the
ASHRAE 90.1 committee for ten years. Mathis has authored over 30 articles and technical
papers on an array of building science subjects ranging from insulation test methods to new
building codes. He conducts training seminars for builders, architects, engineers, and
building officials across the country and worldwide on a variety of building science and regulatory
topics. He has recently been recognized as an ASHRAE Distinguished Lecturer. He
is also one of the principal investigators on a three-year project with the N.C. State Energy
Office to improve the current N.C. Energy Conservation Code by at least 30%.
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INTRODUCTION
Over the past few years, energy codes
have evolved to more highly prioritize building
envelopes, especially their energy efficiency
and the durability of that delivered
efficiency. Unfortunately, the processes by
which codes and standards are developed
can result in a chaotic landscape of requirements
– prescriptive provisions, performance-
based provisions, requirements that
differ from one code to another, and even
requirements that seem internally inconsistent
within the same code. This paper seeks
to quantify the diversity of requirements
currently in the marketplace governing
commercial roof insulation and to assist
building industry professionals involved in
roofing to better understand and navigate
this chaotic and changing regulatory landscape.
Background
Not since 1975 and the development of
the first of our model energy codes for buildings
have architects, specifiers, engineers,
and contractors faced such a chaotic landscape
of energy code requirements. From
the multitude of acronyms and numbers –
ASHRAE, IECC, 90.1, IgCC, 189, Title 24,
FTC, ICC, PV1, MEC (to name a few) – to the
variety of prescriptive requirements and
performance-based approaches to code
compliance, confusion over what is actually
required is often the norm. And where confusion
exists, so exist noncompliance, poor
building performance, and professional
risk.
In 1975, the American Society of
Heating, Refrigerating and Air Conditioning
Engineers (ASHRAE) gave the country its
first national model energy code for buildings.
1 A rapid response to America’s energy
crisis, this code signified what would
become an ever-changing landscape of
requirements – changing as building materials
and systems technology changed, as
well as changing with the cost of energy and
fuels.
States began using the new energy code
with varying degrees of effectiveness. The
language of the early codes was more
aligned with “design guides” than with the
mandatory language of life safety codes.
Minimum attributes for building envelopes,
HVAC systems, and lighting systems
evolved over each version of the ASHRAE
standard (90A-1980, 90.1-1989, etc.).
Then, the energy code landscape changed
completely in 1992.
The fall of 1992 marked a pivotal
moment in the history of Standard
90.1 with the passage of the U.S.
Energy Policy Act of 1992. The
Energy Policy Act contained sweeping
provisions related to energy, in
particular, it contained a requirement
that all states must adopt
energy codes for commercial and
high-rise multifamily residential
buildings at least as stringent as
Standard 90.1. This singular
requirement effectively anointed
Standard 90.1 as the “law of the
land.” Additionally, the Act required
that states must update their codes
when Standard 90.1 was revised
subsequent to a DOE determination
that the new version of the Standard
was more stringent than the old
one.2
With the passage of this law, architects,
engineers, specifiers, and other certifying
professionals faced a new, federally mandated
standard of care. When stamping
drawings and certifying code compliance,
professionals now faced a new compliance
question: “Does this meet the latest version
of ASHRAE 90.1 – even if my state has not
yet adopted it?” Architects, engineers, specifiers,
and others began to pay much more
attention to the latest update from ASHRAE
to make sure they protected their own professional
liability.
States now faced the federal requirement
to adopt and regularly update their
state energy code requirements to match or
exceed the requirements of each new 90.1
update. Unfortunately, state code cycles
didn’t always mesh with the latest version of
ASHRAE. In fact, even though work on the
standard continued nonstop for ten years
(1989 to 1999), ASHRAE didn’t publish a
new version of the Standard. When 90.1-
1999 was published, a new round of DOE
evaluations, state code updates, and new
requirements began.
ASHRAE then put the standard on “continuous
maintenance” to better mesh with
the now-common three-year code development
cycle of the ICC and many states, and
has published a new version of the standard
every three years since 1999. By the time
this paper is published, ASHRAE 90.1-
20103 should be published and starting the
state code-review and update cycle once
more. And certifying professionals will now
have a new standard against which they
must certify energy code compliance.
All of this background on ASHRAE is
just a preamble to the fact that chaos
regarding energy code provisions still reigns
in the local code marketplace. Some states
have complied with the federal requirements.
Others have lagged behind, some
not updating their energy codes for decades.
Some states have attempted to stay ahead
of ASHRAE and the federal requirements,
adopting and maintaining their own state
codes. (These states are often a laboratory
for new code requirements that end up as
proposals to the national model codes.)
Over the past decade, an increased
understanding has grown of the critical role
that our nation’s buildings play in our total
energy use, fossil fuel demands, electricity
demands, and national energy security.
Building energy performance has become a
higher priority, shown clearly by the growth
of product and building energy-labeling programs
(such as Energy Star®).
A new contributor to the chaos of building
energy requirements is the growing
“sustainability” movement. A diverse array
of green building programs has each sought
to define minimum energy requirements
beyond those defined by the energy code.
While the provisions of each green program
vary, they often present yet another set of
performance requirements for architects,
specifiers, and engineers (see below).
A look at the evolution of the prescriptive
requirements for one building variable –
roof insulation – will demonstrate some of
the reasons that specifiers can become eas-
ROOFS, ENERGY EFFICIENCY, CODES, AND SUSTAINABILITY:
COMPLEXITY AND COMPROMISE ON THE ROAD TO NET ZERO
ily confused when trying to identify “minimum
requirements.”
Current Regulatory Landscape for Roof
Insulation
While there are multiple ways of complying
with a given energy code, by far the
most common is the “prescriptive path.”
Using this path, specifiers and contractors
merely select from a table of minimum values
for a given building component to determine
code requirements. Table 1 shows an
example of the requirements for the opaque
elements of a building envelope from
ASHRAE 90.1-2004 for climate zone 3,
which includes Charlotte, NC; Atlanta, GA;
Little Rock, AR; and most of California.
Here, a specifier would select the building
system being used for each component,
and the table then identifies the minimum
energy performance requirements. (Note:
The performance requirements are generally
defined by the component U-factor, with
R-value shown defining the requirements in
“purchasable units” for various construction
systems.)
In this example, roofs for commercial
buildings with insulation installed entirely
above deck must have a U-factor of the
0.063 Btu/hr*sq ft*F. The R-value requirement
shown (from analysis of the most costeffective
construction system to meet this
performance objective) is R-15 ci, meaning
“continuous insulation over the entire deck
having an R-value of at least 15.”
Interestingly, this particular value had
remained unchanged since 1989 – almost
20 years. So it is easy to see why many in
the marketplace think that R-15 is the prescriptive
requirement. That is no longer
true.
Following publication of the 2004
Standard, ASHRAE began a new look at the
cost of energy, construction economics, and
minimum performance attributes. Already,
the marketplace was reassessing and reprioritizing
durable building envelopes as a
key area for improved energy efficiency.
This same table from the 2007 standard4
showed changes to the minimum
requirements for the first time in almost 20
years. Now, roofs with insulation above
deck must have a U-factor of at most 0.048
Btu/hr8sqft*F and translating to continuous
insulation of at least R-20.
Some states had already adopted state
codes that surpassed these slight R-value
improvements. Other states lagged behind,
failing to update their energy codes or, even
if updated, failing to exert much compliance
pressure.
Simultaneously, the International Code
Council (ICC) was continuing its regular
efforts at updating the International Energy
Conservation Code (IECC). (It should be
noted that the IECC also has federal law reference
status. Under the Energy Policy Act
of 1992 [the same law defining ASHRAE
90.1 as the federal standard of care], the
“Model Energy Code” was similarly referenced
as the standard for one- and twofamily
dwellings against which state codes
would be compared. The MEC evolved in the
IECC, which now includes residential and
commercial building energy requirements.)
It is critically important to understand
how this seemingly chaotic regulatory landscape
could easily result in confusion over
minimum requirements. While this paper is
only looking at one prescriptive attribute,
this same potential confusion exists for
Table 1 – A portion of ASHRAE 90.1-2004 Prescriptive Requirements – CZ3
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Table 5.5-2 Building Envelope Requirements for Climate Zone 3 (A, B, C)
Nonresidential Residential Semiheated
Assembly Insulation Assembly Insulation Assembly Insulation
Opaque Elements Maximum Min. Maximum Min. Maximum Min.
R-Value R-Value R-Value
Roofs
Insulation entirely above deck U-0.063 R-15.0 ci U-0.063 R-15.0 ci U-0.218 R-3.8 ci
Metal building U-0.065 R-19.0 U-0.065 R-19.0 U-0.097 R-10.0
Attic and other U-0.034 R-30.0 U-0.027 R-38.0 U-0.081 R-13.0
Walls, above-grade
Mass U-0.151 R-5.7 ci U-0.123 R-87 ci U-0.580 NR
Metal building U-0.113 R-13.0 U-0.113 R-13.0 U-0.184 R-6.0
Steel-framed U-0.124 R-13.0 U-0.084 R-13.0 + R-3.8 ci U-0.352 NR
Wood-framed and other U-0.089 R-13.0 U-0.089 R-13.0 U-0.089 R-13.0
Walls, below-grade
Below-grade wall C-1.140 NR C-1.140 NR C-1.140 NR
Floors
Mass U-0.107 R-6.3 ci U-0.087 R-8.3 ci U-0.322 NR
Steel joist U-0.052 R-19.0 U-0.052 R-19.0 U-0.069 R-13.0
Wood-framed and other U-0.051 R-19.0 U-0.033 R-30.0 U-0.282 NR
Slab-on-grade floors
Unheated F-0.730 NR F-0.730 NR F-0.730 NR
Heated F-1.020 R-7.5 for 12 in. F-1.020 R-7.5 for 12 in. F-1.020 R-7.5 for 12 in.
Opaque doors
Swinging U-0700 U-0.700 U-0.700
Nonswinging U-1.450 U-0.500 U-1.450
every element of buildings having performance
requirements governed by the code.
“Which code does my state reference?”
“What are the latest ASHRAE values?” “Are
these also in the IECC?” “But what if my
state has not updated the state requirements?”
“Is my state code more stringent
than the latest version of 90.1?” All these
are perfectly reasonable questions to ask in
an almost constantly changing code landscape.
Current Requirements
Figure 1 shows the changes to this one
construction element over the past few code
development cycles. (Note: The values for
ASHRAE 90.1-2010 had not yet been published
at the time of this writing, but these
are the values approved by the development
committee, approved through the various
ASHRAE technical and standards committees,
and handed up to the ASHRAE board
of directors for final approval.)
It is significant to note some of the reasons
for this shift in minimum performance
requirements.
First, the standard became dramatically
more robust and detailed over time. In
1989, there was only one roofing requirement
per climate zone. (Note: There were 38
climate zones!) In 1999, the number of climate
zones had been reduced to 26, but the
Figure 1 – 2004 to 2010 ASHRAE minimum requirements for above-deck
insulation.
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Table 5.5-3 Building Envelope Requirements for Climate Zone 3 (A, B, C)
Nonresidential Residential Semiheated
Table 2 – Portion of ASHRAE 90.1-2007 Prescriptive Requirements – CZ3.
Assembly Insulation Assembly Insulation Assembly Insulation
Opaque Elements Maximum Min. Maximum Min. Maximum Min.
R-Value R-Value R-Value
Roofs
Insulation entirely above deck U-0.048 R-12.0 ci U-0.048 R-20.0 ci U-0.173 R-5.0 ci
Metal building U-0.065 R-19.0 U-0.065 R-19.0 U-0.097 R-10.0
Attic and other U-0.027 R-38.0 U-0.027 R-38.0 U-0.053 R-19.0
Walls, above-grade
Mass U-0.123 R-7.6 ci U-0.104 R-9.5 ci U-0.580 NR
Metal building U-0.113 R-13.0 U-0.113 R-13.0 U-0.184 R-6.0
Steel-framed U-0.084 R-13.0 + R-3.8ci U-0.064 R-13.0 + R-7.5 ci U-0.124 R-13.0
Wood-framed and other U-0.089 R-13.0 U-0.089 R-13.0 U-0.089 R-13.0
Walls, below-grade
Below-grade wall C-1.140 NR C-1.140 NR C-1.140 NR
Floors
Mass U-0.107 R-6.3 ci U-0.087 R-8.3 ci U-0.322 NR
Steel joist U-0.052 R-19.0 U-0.052 R-19.0 U-0.069 R-13.0
Wood-framed and other U-0.051 R-19.0 U-0.033 R-30.0 U-0.066 R-13.0
Slab-on-grade floors
Unheated F-0.730 NR F-0.730 NR F-0.730 NR
Heated F-0.900 R-10 for 24 in. F-0.900 R-10 for 24 in. F-1.020 R-7.5 for 12 in.
Opaque doors
Swinging U-0700 U-0.700 U-0.700
Nonswinging U-1.450 U-0.500 U-1.450
number of construction types were expanded.
By 2010, there were three different
specifications for three different categories
of roof construction for each of the (now)
eight climate zone classifications.
Secondly, over time, building envelope
provisions became more highly prioritized
in the standard. ASHRAE’s economic analysis
techniques evolved over time. These economic
tools consider, among other things,
the life expectancy of various building components
to determine the most cost-effective
set of construction minimums. So the
development committee had to ask tough
questions like: “How long does this building
provision last?” “How long does a building
envelope last?” “How long does a heating
system last?”
Prior to 2010, building envelope provisions
had been evaluated on a 30-year life
cycle basis. (HVAC, lighting, and other provisions
were each evaluated at different life
expectancies, based on the technology and
professional experience.)
Review of U.S. Census and construction
data show that the average age of commercial
buildings in the United States is well
over 75 years, suggesting that the 30-year
economic assumption was now fully valuing
building envelope decisions. New economic
boundary conditions were established and
40 years was selected for evaluating building
envelope measures.
Additional contributors to these
changes in building envelope provisions
included the cost of energy and the cost of
money. Our ever-increasing demand for
electricity combined with re-establishing
pre-embargo levels of reliance on foreign
fuel supplies influenced the energy cost
assumptions. Natural gas, oil, and electricity
prices were on the rise. The scalar ratios
used in ASHRAE’s National Energy Model
were adjusted by newly revised economic
inputs such as fuel escalation rates (heating
and cooling), the general inflation rate, the
discount rate, interest rate, and state and
federal tax rates.
All of these different forces combined
placed a higher value on the energy efficiency
and performance of building envelopes
than ever before. New minimum performance
values were defined in the code.
Higher levels of insulation were now
demanded (along with better windows, better
air sealing, better walls, and other
improved building envelope components.)
State and national model codes began, once
again, to assess and update their minimum
performance requirements.
From Minimum Code to a “Green”
Marketplace
As previously mentioned, the past
decade also saw an emerging market force
called “green.” Sustainability became the
new buzzword and industries scrambled to
address the new trend. “Beyond code”
became a fundamental building block of
every green building program. “How far
beyond code?” became the question asked
in each program. 10%? 15%? 30%? More?
Unfortunately, this questioning resulted
in even more confusion for architects, engineers
and specifiers seeking to participate
in these emerging green building programs.
Which baseline? The 2004 ASHRAE? 2007?
How many LEED® points is this worth? How
many carbon credits? Would someone
please tell me what I need to build to get my
green label?
Once again, ASHRAE and ICC tried to
address the regulatory vacuum and the
growing demand for a “green code.”
ASHRAE began work on Standard 189.1,
trying to address minimum requirements
for attributes that had not (typically) been
parts of normal ASHRAE standards development
activities. Issues such as water conservation
and soils protection entered the
discussion, along with the familiar energycode
topic. In fact, deciding on beyond-code
energy provisions was seen by many as the
easiest part of the 189.1 development activity
– it was familiar ground. After years of
developmental effort involving thousands of
man-hours, ASHRAE published Standard
for the Design of High Performance Green
Buildings Except Low-Rise Residential
Buildings in 2009.5
Like other green-building programs,
Standard 189.1 defines minimum energy
performance objectives that are more efficient
than the minimum code (Standard
90.1).
Figure 2 shows the prescriptive values
for above-deck roof insulation defined in
Standard 189.1 and compared to the previously
cited versions of the 90.1 requirements.
As can immediately be seen, another
source of confusion emerges for architects,
engineers, contractors, and specifiers. In
some cases, the prescriptive values for the
green code are not as good (efficient) as the
values in the minimum code.
The explanation, while simple, demonstrates
a new challenge to be faced by all
specifiers – constant vigilance. While the
189 committee was working feverishly to get
the first green code published, the standards
development committee working on
the next round of revisions to 90.1 also continued
its work. Just months after publication
of 189.1, the new “beyond-code” standard
at ASHRAE, 90.1-2010, was being put
to bed with even higher minimum R-values
than the green code.
While most of the minimum insulating
values are essentially the same between
189.1 and 90.1, note Climate Zones 4 and
5, which cover most of the U.S. from
Virginia to Nevada and northern Georgia to
Chicago. The minimum code now says R-
30. The green code is only at R-25. Isn’t
green supposed to be better than minimum?
While this difference can easily be
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Figure 2 – Above-deck insulation requirements: Standard 90.1 versus 189.1.
attributed to development and publishing
schedules, the fact remains that specifiers
should be cautious and conservative when
certifying code compliance. The need for
caution is especially amplified by the
renewed focus on the building industry’s
role in our national energy picture and the
ever-increasing desire to get to “net zero”
energy buildings.
The Road to “Net Zero”
Designers across the country, and
indeed, around the world, are seeking new
ways to achieve the “ultimate” in building
energy performance – net zero energy buildings.
By its simplest definition, “net zero”
simply means that the building (and the
systems it employs) generates as much
energy as it takes to operate the building.
An array of emerging energy and power
production technologies are showing up on
buildings seeking to achieve this consumption
versus generation balance. From photovoltaic
systems to wind turbines to combined
heat and power systems and many
others, these technologies offer the promise
of greater energy security – a sort of hedge
against energy inflation and potential fuel
disruptions.
But the effectiveness and impact of all of
these new power production technologies
depend significantly on one thing – a fundamentally
energy-efficient building from
the start.
It makes no sense, economically or otherwise,
to use any of these great, new power
production technologies on a building that
is an energy hog from the start. Similarly,
why put fancy PV or wind power systems on
a roof that isn’t first sufficiently insulated?
The Starting Point
If we are to ever get to “net zero” buildings,
we must have dramatically better
building envelopes. We must also be ever
mindful that the code values are the minimums
– the starting point. The code does
not define high quality levels of energy efficiency
– it defines the least efficient allowed.
The new standard of care for specifiers
will be ASHRAE 90.1-2010. It defines the
starting point. For above-deck roof insulation,
those values will be as shown in Table 3.
The climate zone map from the code is
reproduced in Figure 3 for ease of projecting
these requirements to other locales.
CONCLUSIONS
Specifiers can easily be confused over
the array of potential requirements defined
in the energy code. Certification of code
compliance requires that the professional
standard of care be recognized and
employed. Regardless of which local code
might be in place in a given state, certifying
professionals should we aware and
informed about these critical national standards
that can impact non-compliance liability.
Voluntary or codified building programs
that seek energy performance levels beyond
minimum code should also be carefully
scrutinized by raters and certifiers.
Compliance with beyond-code objectives
demand first a full understanding of current
code minimums referenced in federal law.
When published, the new standard of
care for certifying professionals seeking compliance
with the latest energy code will be
ASHRAE 90.1-2010. The prescriptive
requirements for commercial roofs with
insulation above deck will likely range from
R-20 in Miami to R-35 in the far north.
Regardless, the values will surely be different
from what has been common practice,
even over the past ten years. Building professionals
should become immediately fluent
in these new prescriptive code requirements.
REFERENCES
ASHRAE Standard 90.1-2007, American
Society of Heating Refrigerating
and Air Conditioning Engineers,
Atlanta, GA.
ASHRAE Standard 90.1-2010 (P),
American Society of Heating Refrigerating
and Air Conditioning
Engineers, Atlanta, GA.
ASHRAE Standard 90-1975, American
Society of Heating Refrigerating and
Air Conditioning Engineers, Atlanta,
GA.
The International Energy Conservation
Code 2009, International Code
Council, Country Club Hills, IL.
Ronald E. Jarnagin, “1992 Energy
Policy Act and 90.1-1999,” ASHRAE
Journal, March 2010, Page 41.
Standard for the Design of High
Performance Green Buildings Except
Low-Rise Residential Buildings,
American Society of Heating Refrigerating
and Air Conditioning
Figure 3 – U.S. Climate Zone Map from ASHRAE 90.1 and IECC.
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Climate Zones 1 2 3 4 5 6 7 8
Example City Miami Houston Atlanta St. Louis Chicago Minneapolis Anchorage Nome
Minimum R-Value R-20 R-25 R-25 R-30 R-30 R-30 R-35 R-35
Table 3 – Minimum R-values for above-deck roof insulation in ASHRAE 90.1-2010.
Engineers, Atlanta, GA, 2009.
P. Torcellini, M. Deru, B. Griffith, K.
Benne, M. Halverson, D. Winiarski,
and D.B. Crawley, “DOE Commercial
Building Benchmark Models,”
ACEEE Summer Study on
Energy Efficiency in Building,. 2008.
FOOTNOTES
1. ASHRAE Standard 90-1975, American
Society of Heating Refrigerating
and Air Conditioning Engineers,
Atlanta, GA.
2. Ronald E. Jarnagin, “1992 Energy
Policy Act and 90.1-1999,” ASHRAE
Journal, March 2010, Page 41.
3. ASHRAE Standard 90.1-2010 (P),
American Society of Heating Refrigerating
and Air Conditioning
Engineers, Atlanta, GA.
4. ASHRAE Standard 90.1-2007,
American Society of Heating Refrigerating
and Air Conditioning
Engineers, Atlanta, GA.
5. Standard for the Design of High
Performance Green Buildings Except
Low-Rise Residential Buildings.
American Society of Heating Refrigerating
and Air Conditioning
Engineers, Atlanta, GA, 2009
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