This course is part of the Commercial Roofing Academy

VOCS OUTSIDE

The term “VOC” is a universal label applied to this class of compounds, but the reasons these compounds are of concern are different outdoors. Whereas the main concern indoors is the risk to humans from directly inhaling, drinking, or absorbing the toxins in the VOC, outside VOCs pose less of a threat in this way. Natural ventilation helps disperse the chemicals quickly, diluting the concentration of the toxins so that under normal conditions they don’t pose a threat to human health.

The main concern with VOCs outdoors is how they serve as a main ingredient in creating the problem of photochemical smog.

On normal sunny days, the air can be clean and healthy, but when VOCs are introduced, a photochemical reaction starts. These VOCs can be from industrial facilities, electric utilities, motor vehicle exhaust, gasoline vapors, and, like the VOCs indoors, chemical solvents and adhesives. When these VOCs are mixed with oxides of nitrogen (an abundant and naturally occurring chemical in the air) or carbon monoxide (a byproduct of combustion engines plus the addition of heat from sunshine), ozone is created.

Photo courtesy of Versico Roofing Systems

Specifying low-VOC adhesives can help contribute to both a healthier environment and sustainability goals on the project.

There are two kinds of ozone. One called stratospheric ozone is beneficial for our planet and occurs naturally in the upper atmosphere. This “good” ozone forms a protective layer that shields us from the sun's harmful ultraviolet rays. The other type of ozone is ground-level or tropospheric ozone. This is considered “bad” ozone and proves the main ingredient in smog. Smog can be created by a mixture of other chemicals, but for this article, we can consider the terms photochemical smog and ozone to be interchangeable.

Ozone can create all sorts of health issues for humans, vegetation, and the environment. For humans─depending on the level of exposure─ozone can cause coughing and a sore or scratchy throat, make it more difficult to breathe, inflame and damage airways, and leave lungs more susceptible to infection. For people with existing conditions such as asthma, emphysema, and chronic bronchitis, the impact of ozone can be sudden, severe, and persistent. However, some of these effects have been found even in healthy people without these conditions.

For the environment, elevated exposures to ozone can affect sensitive vegetation and ecosystems, including forests, parks, wildlife refuges, and wilderness areas. Ozone can reduce photosynthesis, slow plant growth, increase plants' risk of disease, and make them more vulnerable to insects, drought, and harm from severe weather.

Also, tropospheric ozone is the third most important anthropogenic greenhouse gas after carbon dioxide and methane. It absorbs infrared radiation from the Earth's surface, reducing the amount of radiation that escapes to space.

Because of the negative impact that ozone can have on people, plants, and the planet, the EPA is heavily invested in reducing photochemical ozone, which means regulating VOCs. Roofing adhesives, sealants, and glues fall into this category of VOCs that potentially can create photochemical smog, and as we’ll see, there is frequently some confusion over exactly which chemicals are defined as VOCs, and which VOCs are regulated.

REGULATING VOCS OUTSIDE

Under the authority of the Clean Air Act (CAA), the EPA was directed to define and regulate outdoor air pollutants, including VOCs. In the 1970s the EPA started to list several chemical compounds that it deemed to be contributors to photochemical ozone. To do this, a threshold of reactivity, or volatility, was established to determine which compounds would be regulated, and those that would be exempt.

The list of VOCs on the EPAs list has grown and shrunk over the years as different chemical compounds have been evaluated, and the industry has challenged and petitioned for changes and exclusions to the list. Since 1977 there have been about 70 compounds that have been given exemptions because they have a negligible level of reactivity, meaning they fall below the threshold of presenting an actual threat to creating ozone. The intent of the exemptions was the belief that exempting such compounds creates an incentive for industry to use materials that won’t create photochemical ozone. Hence the creation of low or no-VOC labels on building materials.

The EPA originally defined the regulated organic compounds in outdoor air as “Reactive Organic Gases” (ROG). However, later changed that terminology to VOC, based on the relative nature and volatility of the compound. It is useful to note for background that while this change in terminology did clarify the focus of regulation to a more uniform and specific understanding of the compounds, using the term VOC rather than ROG has created some confusion in the industry.

The EPA has no authority to regulate household products when applied to indoor air quality, but the agency does regulate outdoor air quality. Although the same term “VOC” is used for both indoor and outdoor air quality, the term is defined differently to reflect its predominant concern in each context. Inside VOCs impact the health of the occupant, while outside VOCs contribute to the creation of ozone. The misunderstanding about this difference by some individuals and organizations, including manufacturers of building materials and products, is because the word VOC is used for both indoor and outdoor air quality purposes.⁵

Once the list of outdoor VOCs that contribute to photochemical ozone was established, the EPA then began monitoring levels nationwide to determine where and how to focus regulatory attention. The National Ambient Air Quality Standards (NAAQS) were defined and set limits on the concentrations of specific air pollutants in the outdoor air that are considered safe for public health and the environment. A region, usually a state, in which ground-level ozone is found to exceed the NAAQS, is said to be in nonattainment and required to develop a plan to reduce ozone levels. Individual states are required to develop State Implementation Plans (SIPs) outlining how they will achieve and maintain compliance with the standards.

For architects, builders, manufacturers, and suppliers, VOC regulation can vary depending on the jurisdiction and local codes. Because of high levels of ozone especially in areas of dense populations, heavy traffic corridors, or industry, some areas decide to go beyond NAAQS standards and enact even more stringent or specific guidelines for VOCs. In these regions, there can be regulatory groups developed that help set specific collective guides and standards for VOCs.

Regulatory Bodies Ozone:

• California Air Resources Board (CARB) is the regulatory body that oversees California’s statewide air quality initiatives and guides the regulatory activities of its 35 local air districts.
• Ozone Transport Commission (OTC) consists of 12 member states and the District of Columbia. The member states are Connecticut, Delaware, Maine, Maryland, Massachusetts, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, Vermont, and Virginia. These states work together to develop and implement strategies to reduce ozone-forming pollutants.
• Lake Michigan Air Directors Consortium (LADCO) is another regional organization in the United States that focuses on air quality issues. Specifically, LADCO addresses air quality concerns in the states surrounding Lake Michigan.
• South Coast Air Quality Management District (SCAQMD) is a government agency responsible for air quality management in the South Coast Air Basin, which includes Los Angeles, Orange County, Riverside County, and San Bernardino County in Southern California. The VOC content limits and regulations in the SCAQMD are among the most extensive and sweeping in the country.

The key takeaway to understanding outdoor VOC regulations is that not all building materials and systems are allowable, even if the product is approved by the EPA. In California, for instance, one type of roofing adhesive may be acceptable and considered low-VOC in Sacramento, but this same material might not be allowed in Malibu. When specifying roofing types and systems, it is critical to do the extra legwork and focus on research to ensure that the system being specified will comply with all federal, state, and local VOC regulations. A good tip for structuring the process to do this is to select a manufacturing partner who understands what is and is not allowed and also understands some of the limitations of installing low-VOC, no-VOC roofing materials.

Craig Tyler, Specification Manager for Versico Roofing Systems, states “Many manufacturers of Roofing will specifically label a SCAQMD compliant or Rule 1168 compliant adhesive for use in those counties, which not only have a limit on VOCs, but a list of chemicals not allowed in the SCAQMD area. Also, keep in mind, there are also many adhesives that will meet the VOC limit threshold (200 g/l) or will contain no VOCs (0 g/l) for the other areas of the country with VOC limit requirements”.

SPECIFICATION FOR SUSTAINABILITY

Incorporating low and no-VOC roofing systems into the overall design of a project can help bolster sustainability, while also looking out for the health and well-being of the environment. As regulations and standards have increased the scrutiny of outdoor VOCs and the creation of photochemical ozone, manufacturers have responded by providing more earth-friendly products.

For commercial roofing, single-ply systems are the most popular, but they also often encounter regulations regarding VOCs. The three consistently specified styles of single-ply roofing are EPDM (Ethylene Propylene Diene Monomer), TPO (Thermoplastic Olefin), and PVC (Polyvinyl Chloride).

Single-ply roofing membranes can be attached to roofing substrates in several ways including mechanical fasteners, loose-laid with gravel (ballasted), or through a variety of adhesive products. These adhesives are typically marketed for use with either PVC, EPDM, or TPO roofing membranes, or for use with both TPO and EPDM roofing membranes.

Most roofing adhesives for EPDM and TPO are site-applied, single-component, and solvent-based. Craig Tyler, with Versico, says “most manufacturers have a water-based membrane adhesive which acts as the solvent, but the installation then has cold weather limitations, meaning it cannot be installed below 40°F (4.4°C) and tends to need more time for the water to “flash-off” than a conventional solvent”. The adhesive is generally applied using a roller or sprayed onto both the roofing substrate and the back-side of the roofing membrane and allowed to dry, or flash-off, until it becomes tacky. The membrane is then applied to the roofing substrate, and pressure is applied until a permanent bond is created.

Fully adhered membranes can provide a more durable roof when compared to mechanical fasteners because the fully adhered membranes tend to distribute uplift pressure more evenly across the membrane. Another benefit from both durability and ease of installation standpoint is that larger sheet sizes and rolls reduce the number of splices to complete the job while leaving fewer seams to seal.

Many of the chemicals used in solvent-based adhesives that single-ply roofing systems utilize contain VOCs, and navigating the path to compliance isn’t always easy. Most manufacturers of adhesives, sealants, and roofing systems provide low-VOC formulations, but that simple label may not mean the product is right for the project. For instance, the EPA sets limits on how much VOC a product can contain at a range of 30 to 250g/L (grams per liter). Under 250g/L, a product could be considered “low-VOC.” But as of 2023, SCAQMD Rule 1168 limits VOC emissions from adhesives and sealants commonly used in EPDM and TPO roofing systems to 200 g/L. Specifically, SCAQMD Rule 102 considers t-butyl acetate, a common additive used in sealants, to be a VOC, whereas it is considered exempt by the EPA. This is where research, documentation, and technical data sheets together become critical when specifying a roofing system in a particular area.

Also, when looking to achieve sustainable and healthy building status, it is important to note that under either definition, many exempt VOCs–those under 250g/L–still have health or environmental hazards associated with them. Just because the material is technically under the exempt limit does not mean it won’t contribute to ozone creation.

BIO-BASED ROOFING SEALANTS

One solution developed by manufacturers to reduce VOCs in roofing adhesives is to create a water-based formula. This kind of adhesive is generally only designed for PVC and certain TPO fleece-backed membranes, but it can significantly reduce the number of VOCs on the job site. Some available formulas of water-based adhesives contain less than 125g/L of VOCs.

Typical installation for water-based adhesives is designed as a one-sided, wet lay-in with no flash-off time. The adhesive must not dry during the application, or the roofing material will not adhere to the substrate. There are also limits to installation in cold weather, including it can’t be installed at less than 40°F and should not be used if the temperature is expected to fall below 32°F during the first 72-hour curing period.

Due diligence is critical when specifying water-based sealants for single-ply roofing systems. There are some products in the marketplace that tout a low-VOC water-based formula, and promote the product as applicable for PVC, TPO, and EPDM systems. Careful examination of the contents may show that though it is water-based and is technically low-VOC, it still contains 250m/L of VOCs.

GETTING CREDIT FOR LOW-VOC ROOFING

As part of the sustainability and durability pursuit, green building programs can provide guidance, direction, and justification for specifying materials and systems that promote a healthy interior, and exterior environment. While there are many programs available that provide certification on indoor air quality specifically VOCs, there are fewer programs that look at photochemical ozone potential. Fortunately, though, LEED v4 does.

LEED, which stands for Leadership in Energy and Environmental Design, is the world’s most widely used green building rating system. LEED is a points-based rating system. With LEED, projects can earn credits across eight categories: carbon, energy, water, waste, transportation, materials, health, and indoor environmental quality.

In LEED v4, the credits related to volatile organic compounds (VOCs) are primarily found in the Indoor Environmental Quality (IEQ) category and the Building Product Disclosure and Optimization section of the Materials and Resources (MR) category. However, these credits apply to VOC only on the interior of the building.

For roofing materials, there are a few options for which specifying low-VOC roofing sealants and adhesives can contribute to earn credits.