Concerns about indoor air quality are as old as the republic. Benjamin Franklin and John Adams are said to have argued the relative merits of sleeping with open windows in 1776.[1] A century later, their institutional progeny at the US Environmental Protection Agency sided more or less with Franklin after studying Sick Building Syndrome concluding that “most indoor air pollution comes from sources inside the building.”[2] Building materials led the EPA list of culprits. Today, as New Yorker contributor Nicola Twilley recounts in the most engaging article you will ever read about hydroxyl radicals (“Pac Man of the atmosphere”), research capabilities are so sophisticated that it is possible isolate with scientific precision the impact on indoor air quality of toasting bread or a squeeze of lime.[3] Still, among the most elusive indoor air contaminants after all these years are a subclass of chemicals known as semi-volatile organic compounds - SVOCs[4] - chemicals that can’t be “controlled” with better ventilation. 

As I explain at length in this month’s WELL Building Institute newsletter, SVOCs, like the more familiar volatile organic compounds (VOCs), are associated with an array of acute (asthma) and long-term (endocrine disruption) health hazards. They differ, however, in important ways that have a critical effect on efforts to prevent human exposure. To simplify, the “volatility” of VOCs means that they are typically emitted by “off-gassing” into the air at room temperature, dissipating over time as the molecules break down or air is exchanged. Concentrations of VOCs tend to be highest in, and released at higher levels from, new products. Exposure occurs primarily through inhalation. Some SVOCs carry an added hazard factor of “persistence,” meaning that they last virtually forever in the environment.[5]
The “semi-volatility” of SVOCs makes them more difficult to measure than VOCs because they are released slowly from their sources, over long periods of time, through routine wear and tear, and at variable rates that are not well understood. Methods of estimating SVOC exposure in the built environment “remain limited.”[6] Exposures are typically estimated by measuring SVOC concentrations in household dust. SVOCs can adhere to indoor surfaces and dust. These can be both ingested by mouth directly from the air and from food, as well as absorbed through the skin. They can persist in the built environment, even long after the source has been removed.[7] 

This presents challenges to certification systems for products. Certifiers of “low-emitting” products are clear on their own websites that products are being evaluated for VOCs. However, this does not tell the whole emissions story. A product might be certified as “low-emitting” (for VOCs) but still be a significant source of SVOC emissions, especially with regard to high surface areas where carpets, resilient flooring, and wall coverings can be important sources of phthalates, used to soften vinyl, and PFAS, (per- and polyfluoroalkyl substances) used as stain repellents.[8] Healthy Building Network’s own HomeFree hazard spectrum offers more rigorous screening of SVOCs using a class-based approach to eliminating chemical hazards, as opposed to reducing their emissions. A hazard-based approach to avoiding SVOCs is also used by the International Living Future Institute’s (ILFI) Living Product Challenge and Cradle 2 Cradle product certifications, as well as the Perkins+Will Precautionary List. 

Building certification standards such as LEED and the WELL Building Standard are also challenged by SVOCs. Neither SVOC reduction nor elimination is a prerequisite to achieving certification. LEED addresses the chemicals obliquely, through product optimization credits. WELL v2 takes a better approach, rewarding SVOC avoidance within its Materials Concept with an explicit, though not mandatory, SVOC avoidance feature for phthalates and flame retardants. Unfortunately this feature does not address stain repellents, even though these products can be significant sources of SVOCs, and products free of those materials are now routinely available. Curiously, features in WELL v1 that encouraged avoidance of SVOC flame retardants[9] and PFAS stain repellents have been eliminated from WELL v2.[10] WELL v2 is currently in its pilot phase, and hopefully can still be improved to meet consumer demands.

Consumer concern is driving product innovations that reduce or eliminate SVOCs. Phthalates have largely been eliminated from most vinyl flooring products. Many carpet manufacturers are eliminating PFAS stain repellents. Changes to California regulations have eliminated toxic flame retardants from much of the furniture supply, and most recently, no longer require them in foam board insulation used underground. Product and building certifications must do more to reward and incentivise leadership on SVOC elimination as a foundation of healthy building practice, for example by making such credits prerequisites to certification. This principle is as old as the republic. As Benjamin Franklin put it, perhaps as he opened a window before retiring for the evening, “An ounce of prevention, is worth a pound of cure.” 


[1] Nicola Twilley, “The Hidden Air Pollution In Our Homes,” The New Yorker, April 8, 2019,

[2] Indoor Air Facts No. 4, Sick Building Syndrome, US EPA, February 191

[3] Twilley, “The Hidden Air Pollution In Our Homes.”

[4] Different regulatory agencies define volatile organic compounds (VOC) and semi-volatile organic compounds (SVOCs) differently. For the purposes of this article, we use the definition adapted by the US EPA from the World Health Organization (WHO): 
  • Very volatile organic compounds (VVOCs)Boiling point range (BP) <0 to 50-100°C
  • Volatile organic compounds (VOCs) BP 50-100 to 240-260°C
  • Semi-volatile organic compounds (SVOCs) BP 240-260 to 380-400°C
[5]  See: “POPs (persistent organic pollutants) remain in the environment for extended periods of time, taking decades or even centuries to be degraded.” Two classes of highly persistent SVOC chemicals that occur in indoor environments are PFOS used as stain repellents: (“chemicals are very persistent in the environment and in the human body – meaning they don’t break down and they can accumulate over time”) and brominated flame retardant:  (“They can be highly persistent, bioaccumulative and cause adverse effects in humans and wildlife.”)

[6] R. E. Dodson, D. E. Camann, R. Morello-Frosch, J. G. Brody, R. A. Rudel, “Semivolatile Organic Compounds In Homes: Strategies For Efficient And Systematic Exposure Measurement Based On Empirical And Theoretical Factors”,  Environmental Science and Technology,  2015, 491113–12210.1021/es502988r,

[7] LBNL Indoor Environmental Group, SVOCs and Health, 2019

[8] Louisa Luccatini, “A Review Of Semi-Volatile Organic Compounds (SVOCs) In The Indoor Environment: Occurrence In Consumer Products, Indoor Air And Dust”, Chemosphere, 201, June 2018, 466-482,

[9] See Materials optimization Feature 10, part 2 “Managing Semi Volatile Organic Compounds - SVOCs” 

[10]  It is somewhat confusing that certain SVOCs including flame retardants, PFAS, and phthalates are addressed in the Materials feature of the Air concept in WELL v1, (see Feature 25 while in WELL v2, only phthalates are addressed as an explicit SVOC feature which is identified as Part 2 of Measure 10, (Volatile Compound Reduction) that is contained within the Materials concept. See: (p.56)