Beyond “Cool” and “Sustainable” to High-Performance Roofing 

The Next Stage in Low-Slope Commercial Roofing 

Cool roofing and sustainable (or “green”) roofing emerged as separate, but closely related, commercial roofing industry trends about 10 years ago. Today, both cool and sustainable roofing continue to gain momentum, and they are driving change in commercial roofing market dynamics, roof system design and manufacture, product innovation, industry initiatives, selection priorities, building codes and legislation. They are also sparking a considerable degree of discussion, disruption and controversy due to their ongoing impact on the commercial roofing industry. 

As industry groups continue to develop universal definitions and objectives for cool and sustainable roofing, government agencies at the federal, state and local level are implementing more standards, regulations and incentives to encourage, or mandate, the use of energy-efficient and/or sustainable roofing systems. These actions, combined with simple but powerful economic factors, are creating increased demand for a new class of High-Performance Roofing (HPR) systems that can satisfy traditional performance criteria – such as installed cost, performance and longevity – as well as relatively newer criteria – such as life-cycle costs, energy efficiency and preservation of the environment. 

High Performance Roofing is part of a larger trend toward High-Performance Buildings – a hot topic among builders and managers involved in the construction and renovation of school systems and government facilities. The benefits and objectives of High-Performance Buildings and “whole-building design” include: 

• Energy consumption reductions of 50 per cent or more.
• Reduced maintenance and capital costs.
• Reduced environmental impact.
• Increased occupant comfort and health.
• Increased employee productivity.

 

High-Performance Roofing systems can contribute significantly toward all of these objectives. As part of a High-Performance Building, an HPR system acts as a vital, performance-enhancing umbrella that protects the facility from the elements, enhances the performance of other building components, enables uninterrupted operations, and contributes to the health and performance of occupants. 

Contrary to some popular myths, HPR systems that are cool and sustainable do not necessarily involve additional costs. In fact, one essential definition of a High-Performance Roofing system is that it reduces life-cycle costs (LCC) significantly without substantial trade-offs in performance or longevity. 

HPR protective umbrellas have five important, closely related attributes that make them cost-effective, leak-proof, reliable, long-lasting and environmentally friendly. They are called the “Five Es,” and they can help building owners make informed roofing choices – Energy, Environment, Endurance, Economics and Engineering.

 

HPR 1 – ENERGY

Today, energy conservation is important for a variety of reasons. Roofing can contribute to the energy efficiency of buildings, as well as overall sustainability performance, in two important ways: insulation and reflective (cool) surfaces. 

Insulation is an important component of all roofing systems, especially for reducing heat loss by convection in winter months, but also by controlling heat gain through conduction in the summer. 

According to noted roofing technical authority Carl G. Cash in his book, )Roofing Failures, thermal insulation performs several other important functions in a roofing system, acting as:

• A structural bridge across deck corrugations or discontinuities.
• An attenuating layer between the deck and the membrane.
• A reservoir to handle seasonal moisture variation within the system.
• Structural support for the roofing membrane and any static or dynamic loads applied to the system.

 

Long before cool roofing became a buzzword to signify reflective roofing surfaces in the mid-1990s, the earliest reflective single-ply roofing systems, notably polyvinyl chloride (PVC), touted energy efficiency as part of their sales pitch. By the late 1990s, cool roofing was the hottest trend in commercial roofing, and white, thermoplastic single-plies began a sustained run as the fastest-growing category of commercial roofing systems. 

Although there is no industry-wide definition, cool roofing is generally understood to involve a white roof that reflects, rather than absorbs, sunlight. This keeps building interiors cooler, with less energy needed for air conditioning. 

While there is some concern that cool roofing has been over-promoted at the expense of insulation, there is little doubt among the technical community that reflective roofing surfaces, used in tandem with roofing insulation, is a powerful tool for reducing energy consumption and improving the environment. There are two primary types of widely-accepted cool roofing products on the market today – protective paints and coatings, and single-ply roofing systems. Related, but different, categories that contribute to energy efficiency include garden roof systems (GRS), sometimes called “green” roofs, and solar-integrated roofs.

 

HPR 2A: ENVIRONMENT/EXTERNAL

A popular adage within the sustainable building and construction movement laments that concepts are hard to define, the objectives are complex, and implementation is difficult to accomplish. Nevertheless, the global sustainability movement continues to gain momentum, especially in Europe and North America, and sustainable roofing is an increasingly hot topic. 

One of the earliest general definitions of sustainable development, by the United Nations Commission on the Environment and Development, dates back to 1987. The UN Commission defined “principles of environmental sustainable development” as: Development that meets the needs of the present without compromising the ability of future generations to meet their own needs.

 

The First International Conference on Sustainable Construction was held in Tampa, Fla., in 1994. Attendees defined sustainable construction as: The creation and maintenance of a health built environment based on ecologically sound principles and resource efficiencies. 

The definition for sustainable roofing most experts cite today is the one used in the proceedings of the Sustainable Low-Slope Roofing Workshop held at the Oak Ridge National Laboratory facility in Oak Ridge, Tenn., in October 1996. At the workshop, a sustainable roof was defined as A roof system that is designed, constructed, maintained, rehabilitated and demolished with an emphasis throughout its life cycle on using natural resources efficiently and preserving the global environment.

 

Life Cycle Assessments (LCAs) are science-based studies designed to measure the environmental impact of a product through its entire life cycle. The objective of an LCA is to examine and uncover all the important environmental factors involved in the production, use and disposal of a product – a “cradle-to-grave” analysis that yields what is called an ecoprofile. In the case of roofing products, some of the important criteria an LCA examines include:

• Material Extraction Costs: Environmental impact of obtaining and transporting raw materials.
• Manufacturing Waste: The amount of wastewater and solid waste generated during the manufacture of the finished roofing product.
• Hazardous Waste: The amount of toxic emissions resulting from the extraction of raw materials, manufacture and transport of the finished product and installation of the roofing system.
• Embedded Energy: The amount of energy required to extract, transport, manufacture, deliver, install, maintain and discard a roofing product during its life cycle.
• Recycling and Re-use: The potential for a used roofing product to be recycled or re-used in another form.

 

LCAs are very complex and results can vary depending on methodology, underlying assumptions and, unfortunately, the source of funding. LCAs are used today primarily as guidelines for establishing or defining standards, and in the design phase of product development. The U.S. Green Building Countil has formed a task group to study the feasibility of applying LCA findings toward practical use in building and construction. Various other industry groups have already concluded that, while LCAs are interesting and useful as guidelines, they are not likely to be adopted for practical purposes by the building and construction industry.

 

In their Primer on Sustainable Building Design, the Rocky Mountain Institute maintains that sustainable roofing can be accomplished in five different ways:

• Recycled content in the roofing product.
• The use of recycled materials, such as thermoplastics or metal.
• Extended service life.
• More efficient use of energy and other natural resources.
• The actual renewal of natural resources.

 

A more thorough, practical guide to sustainable roofing – The Tenets of Sustainability – was published by the International Council for Research and Innovation in Building Construction (CIB) in 2000 after five years of committee work. 

One area where sustainable roofing is making a notable impact on a better environment is the mitigation of urban heat islands. Lawrence Berkeley National Laboratories (LBNL) used infrared photographs from outer space taken by NASA to confirm that most large American cities suffer from the heat island effect. This not only means higher electric consumption for air conditioning, it also contributes to high pollution levels. 

LBNL also determined that cooler roofing surfaces are the most economical, viable means of making a significant, immediate impact on the urban heat island problem. The combined benefits of energy efficiency and the mitigation of air pollution, and the UHI effect are the major reasons for the rising tide of legislation mandating or encouraging the use of cool and/or garden roofing systems. 

Three factors have been identified as the primary causes of UHIs. According to LBNL, reduced vegetation accounts for 56 per cent of the increased heat in a UHI. Dark roofing surfaces account for another 38 per cent of the additional heat, while asphalt roads and parking lots are responsible for just six per cent. Clearly, the most practical, economical means of reducing the UHI effect is a reduction of dark roofing surfaces. Specifically, this would include the use of more reflective cool roofing systems, garden roofing systems and perhaps solar-integrated roofing systems. 

Another way of making roofs more sustainable is better management of materials by using recycled content in making roofing materials, recycling used roofing materials, and reducing waste associated with the manufacture, installation and disposal of roofing systems. 

Oak Ridge National Laboratory recently estimated that between nine and 10 million tons of asphalt roofing waste are sent to U.S. landfills every year, which costs more than $400 million (USD) in disposal fees. Most of this waste derives from asphalt built-up roofing (BUR) and modified bitumen roofs that are removed prior to re-roofing a building. Not included in this estimate are the additional tons of waste generated by other types of roofing systems during both installation and tear-off. Altogether, roofing materials are one of the largest waste categories found in American landfills.

 

While roofing waste cannot be eliminated altogether, there are ways of reducing the amount significantly: 

• Building owners can consider installing roofing systems directly over existing asphalt, metal and/or single-ply systems, depending on the level of saturation and certain other conditions. In many cases, thermoplastic single-ply systems can be installed with full warranties directly over existing roofs.
• Building owners can choose single-ply systems that are custom pre-fabricated to fit each building. Custom pre-fabrication reduces installation waste significantly, with many fewer trips to the landfill required, regardless of the size of the project.
• Building owners can choose a roofing system that can be recycled after its useful life, and re-used for other high-level applications, such as flooring, park benches or new roofing components. Metal and thermoplastic single-ply materials – such as PVC and TPO – are recyclable in the plant, after installation, and after the roof’s useful service. Some manufacturers of metal and thermoplastic roofing systems have initiated recycling programs.
• New technologies have made it possible for thermoset (typically, EPDM), single-plies to be recycled into materials for lower-level use, though the cost can be high.
• In fact, cost effectiveness is a barrier that all recycling programs must overcome before they become practical. This includes the geography of recycling – how far, and at what cost, should recyclable materials be transported before the environmental trade-off becomes negative? Still, most environmentalists argue that the cost effectiveness of recycling is a matter of critical mass – the more we do it, the less costly it will become.
• The use of recycled content in certain modified bitumen roofing systems can also contribute to an overall reduction of waste going to landfills.

 

One way of determining if a roof system is sustainable is whether or not it qualifies for points under the U.S. Green Building Council’s LEED Green Building Rating System. LEED is a voluntary, consensus-based national standard for developing high-performance, sustainable buildings. While LEED does not certify products, buildings can earn LEED certification.

 

Under the current standard, LEED version 2.2 credit categories include:

• Sustainable Sites
• Stormwater Efficiency
• Energy and Atmosphere
• Materials and Resources
• Indoor Environmental Quality
• Innovation and Design Process

 

HPR 2B: ENVIRONMENT/INTERNAL

One of the more neglected aspects of roofing is the positive impact it can have on a comfortable, healthy, productive environment inside buildings, where many people spend most of their days. A High-Performance Roofing system can contribute to a better indoor environment in two ways:

1. Cool, green and perhaps solar-integrated HPR systems help to moderate indoor temperatures, even in buildings without air conditioning. A number of studies have shown a direct relationship between thermal comfort and worker productivity in offices and manufacturing facilities. Comfortable indoor temperatures have been shown to improve overall mental concentration, manual work rates, and manual dexterity, while reducing accident rates and absenteeism.
2. Vented roofing systems can help reduce moisture and mould while relieving positive air press, allowing buildings to “breathe.”

 

HPR 3: ENDURANCE

Many factors affecting the durability and longevity of roofing systems are beyond our control, such as climate, catastrophic accidents and violent storms. In terms of High-Performance Roofing, endurance is the ultimate reflection of the performance of every roofing component or element that can be controlled by intelligent design, manufacture, installation and maintenance.

 

Most green building experts believe that longevity is among the most important factors contributing to the sustainability of any building product, including roofing systems. Long-lasting roofs reduce the rate of landfill waste build-up, as well as the demand for re-roofing projects, with all of the embedded energy that entails.

 

Every year of useful service free of major maintenance and repair work also reduces the life-cycle cost of any roof. According to the survey funded by The Roofing Industry Alliance in Progress in 2005, the average life expectancy of a low –slope roof is 17 years. In January 2006, Roofing, Siding and Insulationmagazine reported a “national average for roof service life” of 12 years. In his book, Roofing Failures, acknowledged roofing technology authority Carl Cash estimated the average service life of specific types of roofing systems, ranging between 12.1 years for spray polyurethane foam to 16.7 years for a five-ply BUR system.

 

More importantly in terms of High-Performance Roofing, Cash suggested that building owners consider the durability range of various systems, a better indication of how long the best roofing systems in each category can be expected to last. By this measure, five types of roofing systems have a high-end range of service longer than 20 years: PVC thermoplastic single-ply, asphalt-glass fibre BUR, SBS polymer-modified asphalt, EPDM thermoset single-ply, and asphalt-organic felt BUR.

 

After analysing over 1500 roofing failures, Cash concluded that there is no accurate means of predicting the longevity of any specific roof, but there are ways of maximizing the potential for a long-lasting roof. His four guidelines for roofing endurance are:

• Peer review of the contract document before bidding by a specialist in roofing technology with no financial interest in the project can eliminate one-third of the problems experienced with roofing systems.
• Use roofing systems, manufacturers, designers and contractors with long, successful track records.
• Use monitors hired by the owner to oversee the installation. Defective workmanship accounts for between 30 per cent (Cash) and 47 per cent (NRCA) of roofing failures. Another way of ensuring proper installation is to use suppliers that train their contractors and inspect every roofing job shortly after completion.
• Buy competence, not price, in the supplier, designer and contractor. Building owners should consider long-term value rather than up-front installed costs.

 

HPR 4: ECONOMICS

Life-cycle costs are the third most important consideration – after installed cost and quality of installation – according to the 2005 Roofing Industry Alliance for Progress survey of building owners. Clearly, economics  is a very important criterion for building owners, and High-Performance Roofing systems must be economical if they are to become viable, real-world options. 

One reason we hear more about the life-cycle costs of building materials and systems is the green building movement. Unlike immediate installation costs, however, life-cycle costing must estimate future considerations, such as longevity, maintenance and repair, and the long-term impact on overall facility operations. Life-cycle cost estimates are not as precise as installation cost estimates because variables can change, but life-cycle cost estimates can serve as a useful guide to the value of building system choices over time. 

This is especially true with cool and solar-integrated roofing, where energy savings alone can make a difference in the 20-year cost of a roof. In 2004, a hypothetical, 20-year LCC comparison was prepared with the help of independent Midwest roofing contractors. The contractors did all the estimating based on their years of experience installing and estimating many types of roofing systems. The objective was to compare the life-cycle costs of a High-Performance Roofing system – in this case, a white PVC single-ply – with popular black EPDM and BUR systems for a fully-warranted, 50,000 sq. foot re-roof in the Midwest. 

The PVC single-ply system was chosen because it is an ENERGY STAR-labelled cool roof system with the longest track record, dating back to the early 1960s. The black EPDM and BUR roofs were selected because they currently rank number one and two, respectively, in terms of market share for commercial roofing systems in the U.S. Contractor estimates for the built-up asphalt roofs and EPDM single-plies were averaged. For energy savings, the EPA ENERGY STAR Roof Products Program cool roof energy savings calculator (available on-line at http://roofcalc.cadmusdev.com) was used, projected out 20 years. 

This hypothetical life-cycle cost comparison demonstrates the impact that an energy-efficient, High-Performance Roof can have over time. The total installed cost – the cost of the roof product, installation, tear-off and disposal – are pretty close: $142,500 for the traditional black system; $133,000 for the white PVC cool roof. The main difference is the cost of tear-off and disposal for EPDM and BUR, which normally require a complete tear-off of the old roof before re-roofing. PVC single-ply systems are often installed directly over the existing roof, and require a tear-off only if the local code requires it, or if there is serious damage to the existing substrate. 

Many roofing systems, including EPDM and BUR, require regular repair schedules to maintenance performance. Thermoplastic single-plies are hot-air welded, so repairs are needed only when accidental damage occurs. 

Energy savings are the biggest difference, where the reflective PVC roofing system saves the building owner an estimated $4200 a year. This is actually a conservative estimate considering the continuing upward spiral of energy prices. Not included in the LCC are the less tangible environmental benefits of the High-Performance PVC system – recyclability, reduced landfill waste, less air pollution and mitigation of the UHI effect. 

Another means of achieving better economics is the use of custom pre-fabricated single-ply roofing systems. Precise measurements of each roofing job are sent to the factory in advance. The manufacturer then factory-seams large, custom-fit roof sections of up to 2500 sq. feet under controlled conditions, as well as precisely cut flashings, edging and venting membrane pieces. Designed to fit every roofing job exactly, custom pre-fabricated single-ply roofing systems provide a number immediately, and long-term cost and performance benefits – less waste, less labour, less time and less human error.

 

HPR 5: ENGINEERING

Smart, coordinated engineering and design is not only the essential enabler for every other aspect of High-Performance Roofing it is the key to what the Department of Energy calls “whole-building design,” which integrates all the subsystems and parts of the building to work more effectively together. Roofing authority Carl Cash has estimated that defective design and engineering accounts for about half of all roofing failures.

 

In terms of the other four HPR “E’s”,  engineering and design make an impact in several obvious and less obvious ways:

• Energy

• Specifying premium materials and components to enhance properties such as reflectivity, emittance and ultraviolet radiation.
• Determining the optimal insulation R-values and devising a roof system with the best combination of insulation and roofing membrane for each application based on climate, roof deck and other factors.

• Environment:

• Incorporating materials and components that have a lower impact on the environment based on LCA criteria, such as embedded energy, recyclability and recycled content.
• Incorporating materials and processes that minimize waste of all types.
• Incorporating “green” and “cool” properties into existing roofing systems wherever possible or practical.
• Use of closed-loop manufacturing processes that minimize waste and toxic emissions, and utilize process-generated scrap.
• Incorporating venting to enhance the indoor environment.

• Endurance:

• Designing and specifying roofing systems appropriate for the climate, type of building and roof deck.
• Designing adequate drainage to avoid excessive ponding.
• Incorporating custom pre-fabricated roofing systems that minimize the potential for installation errors, simplify the installation process and minimize waste.
• Specifying premium materials, components and systems to enhance performance and durability properties such as water absorption, fire resistance, tensile strength, thermal expansion, dynamic puncture resistance and resistance to rooftop contaminants.
• Specifying roofing systems with a proven track record of reliable, long-lasting performance.

• Economics:

• Specifying roof systems that can be installed over existing roofs under certain conditions, eliminating tear-off and disposal costs.
• Specifying custom pre-fabricated roofing systems that can be installed quickly, with smaller labour requirements, less disruption to building operations, and fewer maintenance requirements over the long-term.
• Specifying roofing systems that are easy to maintain and repair.

 

SUMMARY: TOWARD A HIGH-PERFORMANCE FUTURE

The demand for energy-efficient, environmentally friendly buildings is creating market demand and government regulations for High-Performance Buildings. Likewise, the demand for cool and sustainable roofing is creating market demand and government regulations for High-Performance Roofing systems that provide optimal functionality with respect to energy, environment, endurance and economics.

 

High-Performance Roofing is a critical part of any High-Performance Building. An HPR system is a protective, performance-enhancing umbrella that protects the High-Performance Building from the elements, enables uninterrupted facility operations, and contributes to the health and productivity of the building occupants. HPR is also one of those rare cases where there does not have to be a trade off between “green” and performance, or “green” and cost. The best HPR systems cost less over time because they reduce energy bills, minimize environmental impact, require less maintenance, and keep the weather outside, where it belongs.