Holistic Roof System Design and Sustainable Roofing Assemblies (formerly known as black roofs vs white roofs)
Although the discussion over roof color has shifted toward holistic roof system design and sustainable assemblies, the older “black vs. white” framing still shapes policy and perception. Revisiting these simplistic arguments helps explain why some stakeholders maintain this view, despite advances in research, materials, and building science. The common nickname “cool roofs” is misleading; “highly reflective white roofs” (HRWR) is the more accurate term.
History
In the early 2000s, manufacturers of highly reflective white roofs (HRWR) gained market share through strong marketing and early research linking lighter colors to cooler buildings. Research methods were still developing, and policies followed a narrow focus on reflectivity.
- Universities, laboratories, and environmental groups studied roof albedo using inconsistent methods and basic climate models.
- Progressive cities enacted HRWR mandates; national model codes measured only reflectivity for energy efficiency.
- Policies ignored other sustainability factors such as embodied carbon, landfill impact, and resilience.
- Early research often relied on flawed assumptions, low insulation baselines, and oversimplified modeling.
- Lower first-install costs and aggressive marketing accelerated HRWR adoption and reduced EPDM market share.
Limitations on the Existing Body of Research
The ERA and Clemson University literature review in 2020 identified recurring limitations in cool roof studies published between 1985-2018. While these studies certainly add to the body of knowledge in some ways, their flaws mean they cannot justify broad mandates requiring HRWRs for entire climate zones or cities. Common limitations include:
- Oversimplified modeling that ignores real-world building complexity
- Geographic data that is too limited to reflect diverse climates
- Short-term studies that miss seasonal and long-term impacts
- Low insulation baselines overstating reflectivity benefits
- Inconsistent measurement of albedo and temperature
- Little consideration of moisture, wind, or precipitation effects
These limitations underscore the need for more nuanced, location-specific policy decisions.
Unintended Consequences of Mandates for Highly Reflective White Roofs
Condensation, Moisture, and Potential for Mold
In Climate Zones 4 and north, HRWRs often need added components to manage moisture, but these are not code-required. Skipping them can create long-term performance issues.
- Missing vapor retarders or air barriers allow condensation to form
- Moisture becomes trapped and cannot dry during summer
- Persistent dampness reduces insulation effectiveness
- Prolonged exposure leads to mold growth and material degradation
Energy Efficiency
In many CZ 3 cases and most CZ 4 and north, added insulation outperforms roof reflectivity in net energy benefit.
- Raising insulation from R-20 to R-30 can cut annual energy use by 10%+ in heating-dominated climates
- Reflective surfaces offer minimal winter benefit and limited summer gains in northern zones
- HRWRs can increase heating demand in cold months, offsetting cooling savings
- Energy modeling shows insulation delivers greater lifecycle savings than reflectivity in CZ 4 and north
Urban Heat
Urban heat islands (UHI) are real, but atmospheric behavior is more complex than a simple shaded-vs.-sun comparison.
- No consistent, in-situ data showing HRWR mandates reduce UHI
- Chicago and New York report no measurable UHI improvement after 15+ years of mandates
- Effectiveness depends on air movement, local climate, and surrounding surfaces
- Increased urban tree canopy provides clear and measurable cooling benefits
Increased urban tree canopy is the factor that makes a big difference in mitigating urban heat islands, but some policy makers have said that it is easier to require HRWR rather than making property owners plant trees.
Current Research
Modern and more recent studies provide a fuller picture of HRWR impacts, showing benefits in some cases but significant limitations and risks when used as a blanket mandate.
- ICF UHI study: no clear link between HRWR mandates and UHI reduction in CZ 3–5
- ICF energy efficiency study: insulation upgrades outperform reflectivity north of CZ 4
- Harvard 2024 study: HRWRs can raise surrounding temperatures, reduce precipitation, and worsen heat inequality
- Tewari et al. 2019: irrigated vegetative roofs more effective for UHI mitigation
- Notre Dame 2016: HRWRs can slow air movement and reduce mixing, affecting air quality
- Yang et al. 2015: benefits depend heavily on climate, urban design, and weather patterns
- Georgescu et al. 2012: large-scale HRWR deployment can reduce rainfall by ~4% in some cities
Current research supports ending broad mandates in favor of flexible, performance-based design
Longevity of EPDM
EPDM roofs have a proven service life advantage, delivering both performance and sustainability benefits.
- Service life of 40+ years vs. 15–20 years for some HRWRs like TPO
- Fewer replacements mean less landfill waste and lower embodied carbon
- Reduces manufacturing and installation impacts over the building’s life
If a single EPDM roof can perform for the same period as two or more TPO roofs, the sustainability advantages are significant, particularly in CZs 3-4 and north, where EPDM can also outperform on energy efficiency without increasing UHI.
Other Benefits of EPDM
EPDM delivers strong performance and long-term value through multiple advantages.
- Durable and resilient in extreme weather
- UV resistant, maintaining performance over time
- Flexible across wide temperature ranges, reducing cracking and splitting
- Easy, cost-effective repairs that can extend service life without full replacement