|
The use of reflective, or “cool,” roofs has become a much-debated
topic throughout the United States in the last several years, due to their presumed
role in providing energy savings, reducing peak energy demand and mitigating the
Urban Heat Island Effect. Many of these attributes are associated with the color
of the roof’s surface. The Solar Smart Roof Alliance (SSRA) believes that
any evaluation of long-term energy savings, peak load reduction or mitigation
of Urban Heat Island Effect must include the entire roof system. In addition,
there has been a notable absence of any cost-benefit analysis in public policy
discussions about reflective roofs, especially in the areas of reflective roof
maintenance and displacement of certain products from the market. SSRA believes
that additional data on these topics are crucial for intelligent decision-making
by the building design and construction communities or by public policy officials
who may use reflective roofs as a regulatory tool.
Choosing the Right Roof
Since the introduction of built-up roofing in the late 1880’s, manufacturers
of roofing products have developed literally thousands of roofing systems based
on the needs of the market. Today, roof designers have a wide choice of roofing
systems: built-up, modified bitumen, thermoplastics such as PVC and TPO, thermosets
such as EPDM, roof coating and spray polyurethane foam roofs. A specific roof
system selection will depend upon a number of design criteria for that building:
building code compliance, fire code compliance, expected lifetime of the roof,
warranty concerns, cost and aesthetics. SSRA is concerned that any action that
limits the choice of roofing systems has the potential to create roof performance
issues or may unnecessarily increase first cost of installation, or long term
operating costs for the building.
Reflective or “Cool” Roofs
At this time, there is no single, agreed-upon definition of a reflective, or
cool, roof. While all attempts at a definition address solar reflectance (or albedo),
emittance is not always included. The most frequently referenced definition is
that used in the Environmental Protection Agency’s Energy Star Roofs Program;
other definitions have originated in regulatory requirements considered in the
City of Chicago and promulgated in the state of California.
SSRA believes a uniform definition of a reflective or cool roof is a necessary
first step in having an informed discussion on the subject. Further, SSRA believes
the overall thermal performance of the roof system should be the focus of the
discussion. When assessing roof performance, R-values of the roof should always
be included. Unfortunately, many buildings do not meet the energy standards of
the American Society of Heating, Refrigerating and Air-Conditioning Engineers
(ASHRAE). SSRA believes strongly that energy performance including minimum insulation
levels as defined in ASHRAE requirements should be a first consideration.
Validation of Energy-Savings Claims
There are widely varying energy savings claims resulting from the use of a cool
roof. EPA’s Energy Star Web site claims energy savings up to 50 percent,
while certain manufacturers of cool roofing products have claimed savings of “up
to 70 percent.” It is not clear if these claims are summer cooling savings
only, or net savings that take into account energy penalties in buildings where
there are significant heating loads. Compounding the problem is the availability
of two government-agency sponsored “Cool Roof Calculators” -- by EPA
and the Department of Energy --that produce different energy savings estimates
when a user selects similar design conditions. This may be the result of different
default values within the calculators. This dilemma not only affects decision-makers
such as architects and building owners, but also affects the manufacturers of
all roofing products.
There is a loss of reflectivity values and energy savings due to degradation
in the reflectance of roofs over time, attributable to aging and dirt accumulation.
In addition, the costs of installing and maintaining cool roofs and restoring
the reflectivity of the roof, need to be factored into considerations of the economic
value of reflectivity. This is true especially where there is high reliance on
the reflectivity to achieve reduced energy consumption, i.e., where high reflectance
is used in lieu of added insulation values.
The confusion in the market about energy savings credited to reflective roofing
systems has the potential for the misuse of reflective roofs, and consequently
of eroding consumer confidence with appropriately installed reflective roofs.
SSRA understands that all computer models and other simulations of energy performance
have limitations and may not truly reflect the performance of occupied buildings.
Therefore, a clear description of assumptions that are used by government calculators
to arrive at estimated energy savings associated with the use of reflective roofing
systems is critical. In the residential market, where the Federal Trade Commission
strictly regulates advertising claims of energy savings to consumers, the complexity
of estimating the effective energy savings is even greater.
SSRA believes that energy savings claims related to the use of reflective roofs,
especially by government agencies, should be substantiated and integrated into
a single, validated, transparent roof energy calculator. All underlying assumptions
and mathematical models should be clearly stated. All limitations due to seasonal
variation and geography should be described. This calculator should be capable
of determining energy use over time as the components degrade from their initial
values.
Regulatory and Other Government Initiatives
A number of government bodies, most notably the state of California and the City
of Chicago, have taken action to require the use of reflective roofs as a means
of saving energy. These initiatives result in a narrowing of choice for the consumer,
which often eliminates roof systems that have been proven to perform over time.
Alternate government choices that result in energy savings, such as non-reflective
roofs with increased insulation, or non-reflective roofs with increased surface
shading provided by the use of ballast, have not been adequately explored.
SSRA believes communities and policymakers need to understand the entire energy
balance of buildings and to use cool roofs as just one tool in determining energy
performance. SSRA believes that climate makes a substantial difference in the
value of reflective roofs and the effect of reflectivity must be carefully considered
before any requirements are in place. Additional information about the accumulated
effect of energy savings, costs and environmental benefits is needed.
Reduction in Peak Energy Demand
The role of reflective roofs in reducing peak energy demand in the short term
has been demonstrated in California. However, any long-term, consistent benefit
depends on the manner in which reflective roofs are maintained. Dirt accumulation
and aging can impact this benefit, as can the effects of other effluents. Care
must also be taken when attempting to extend the California experience to other
parts of the country. For example, it would appear that a cool roof would deliver
the same reduction in peak energy demand in Florida, a state with a climate that
contributes to peak loads resulting from cooling. However, Florida is equally
concerned about peak loads during the heating season, because of the widespread
use of inefficient heating systems. The cost/ benefits need to be weighed in each
community and can be very dependent on the costs of electricity and or other energy
sources.
SSRA believes maintenance, i.e. cleaning, of reflective roof surfaces is a
necessary component of peak load demand reduction. In addition, the relationship
between the continued decrease in peak loads and the reduction in the reflectivity
of cool roof surfaces must be explored.
The Urban Heat Island Effect
The Urban Heat Island Effect is described as a condition in which urban areas
have higher air and surface temperatures than the surrounding rural regions. There
is ample evidence to support the underlying assumption about this phenomenon,
and it is generally agreed that it may contribute to air quality problems. However,
SSRA believes that much more information is needed about Urban Heat Islands before
changes in building codes are warranted, and other mandates are imposed. For example,
information is needed on the extent to which there is a problem in areas where
heating degree days exceed cooling days, and information is also needed about
whether restrictions on the use of certain building materials are warranted.
Measuring Effectiveness of Mitigation Strategies
The spotlight is clearly on the use of reflective roofs as a major contributor
to reducing the Urban Heat Island Effect. However, the lack of empirical air temperature
data for those areas where reflective roofs have been installed has prompted EPA
to use energy savings as a surrogate measure of the effectiveness of reflective
roofs in reducing the Heat Island Effect.
SSRA believes the use of energy savings as a measure of Urban Heat Island Effect
mitigation necessitates the acceptance of all strategies that result in energy
savings, and not just the use of reflective roofs. These include building envelope
insulation, energy efficient HVAC equipment and energy-efficient lighting, among
others.
# # # # # # # # # # # # # # # #
The Solar Smart Roof Alliance is composed of roofing industry
trade associations committed to providing the best information available about
energy and environmental issues pertaining to roof systems. SSRA members are:
- Alliance for the Polyurethanes Industry (API)
- Asphalt Roofing Manufacturers Association (ARMA)
- EPDM Manufacturers Association (ERA) National Roofing Contractors
Association (NRCA)
- North American Insulation Manufacturers Association (NAIMA)
Polyisocyanurate Insulation Manufacturers Association
- PIMA)
- Roof Coatings Manufacturers Association (RCMA)
- SPRI
|
