Roofing and Energy Codes Are Missing Balance
As architects, we continually strive to create buildings that are not only aesthetically pleasing and functional but also resilient and sustainable. One area that often poses challenges is the design of low-slope roofs because requirements set by building codes, energy-conservation codes and other standards are poorly coordinated, often making balanced designs difficult to achieve.
Why Balance Matters
In my experience as a forensic architect specializing in roofing and waterproofing systems, I have encountered numerous underperforming roof assemblies with reduced service lives, falling short of the typical 20-year manufacturer warranty period. The primary reason is the tendency of roof system designers to focus on one or two specific attributes while neglecting others. For instance, designers may opt for highly reflective surfaces or low-VOC materials to meet environmental goals or local requirements without considering climate zone realities or installation limitations. This can lead to omission or downgrading of critical roof system elements, resulting in roof systems that underperform over time.
Addressing this requires a new strategy encouraging balanced consideration across all categories, leading to sustainable and resilient roof assemblies. Achieving the right balance is crucial in new construction and equally essential in reroofing, where additional flexibility is needed to accommodate existing conditions, such as existing drain locations and inlet heights, low curbs, parapet heights, windowsills and door threshold heights, and rooftop equipment and related supports.
The Building Code Framework
Since the International Codes (I-Codes) inception in 2000, the strategy for establishing minimum requirements for low-slope commercial roof assemblies has remained virtually unchanged. Chapter 15 of the International Building Code (IBC) outlines base requirements for designing low-slope roofs, referencing IBC’s Chapter 16 (Structural Design), other I-Codes and relevant standards from ASTM International, the Single-Ply Roofing Institute (SPRI) and the American Society of Civil Engineers (ASCE).
These provisions establish minimum requirements with the primary objective of providing reasonable life safety for building occupants, protecting property from hazards, and safeguarding firefighters and first responders during emergency operations.
The Energy Code Parallel Track
Energy-conservation codes have traditionally been developed separately from building codes. Most U.S. jurisdictions have adopted the International Energy Conservation Code (IECC), which generally applies at the state level with some local jurisdictions making local amendments. The IECC includes three principal requirements for low-slope roof assemblies: minimum thermal resistance, roof solar reflectance and thermal emittance, and air barriers. These requirements apply to roof areas above conditioned space across all state jurisdictions with the roof solar reflectance and thermal emittance requirements only being applicable over cooled conditioned space.
The Reroofing Dilemma
Replacement roof systems are often thicker than those being replaced, primarily because of increased required minimum R-values for roof systems installed entirely above deck. The minimum required R-value for most of the U.S. (Climate Zones 2-6) is R-25 to R-30, equating to approximately 4 1/2 to 5 1/2 inches of insulation, plus other components and flashing heights. This typically defines the thinnest part of roof
systems because additional thickness is often needed for slope to comply with drainage requirements. This is especially true for roofs with fewer drainage points; thickness increases the farther the distance from primary drains or scuppers. This additional thickness poses challenges with parapet wall heights, access doors, windowsills and existing through-wall flashing outlets, making it infeasible to adjust adjacent constructions to meet required terminations and flashing heights.
Balancing Energy Performance and Condensation Control
In Climate Zones 0-3, the IECC requires minimum roof solar reflectance and thermal emittance for roof surfaces above cooled conditioned spaces. However, highly reflective roofs make condensation issues within roof assemblies or spaces below more likely to occur during cold weather.
Research frequently cited by advocates for high roof albedo was conducted more than 20 years ago involving roof assemblies insulated to levels significantly lower than today’s requirements—typically R-8 and below—about three times less than current IECC requirements. The rationale was that reflective surfaces would reduce cooling costs by reflecting solar radiation. However, condensation potential was overlooked.
More recent studies conclude that mandates for reflective roofing in Climate Zone 4 and higher have preempted economic and science-based individualized design decisions based on critical factors, like local geography, building use or materials’ carbon footprint. Recent research repeatedly shows that mandatory reflective roofing has not delivered anticipated benefits for 25 years. Data suggests advantages of highly reflective roofing are best realized when applied selectively, particularly for certain building types in Climate Zones 0-2. The mandated requirement to use reflective surfaces in Climate Zones 3-8 seems outdated and inappropriate.
The Forgotten Factors: Longevity and Service Life
Service life and repairability protect the owner’s investment. When roof assemblies fail prematurely or require extensive maintenance, building owners face unexpected costs far exceeding initial savings. This justifies a fundamental shift from first-cost considerations to life-cycle cost analysis. A roof costing 20 percent more upfront but lasting twice as long delivers far greater value over its lifetime.
Despite its critical importance, service life remains consistently undervalued in building and energy codes because of quantification difficulties. Single attributes, such as R-value or solar reflectance, can be easily measured and mandated. Additionally, roof system resilience considerations have historically been separated from energy code discussions, creating a disconnect between immediate energy performance goals and long-term durability.
However, substantial evidence now supports integrating accurate service life data into balanced design decisions. EPDM roofing systems, for example, have demonstrated exceptional longevity in real-world applications with many installations exceeding 30, 40 years when properly designed and installed. When combined with low maintenance and inherent repairability, durable materials, like EPDM, demonstrate how prioritizing service life creates measurable value for building owners while reducing waste and environmental impact.
Navigating Multiple Goals Simultaneously
When designing roof assemblies, several requirements must be addressed for code compliance. Beyond code concerns, roof system manufacturers have warranty requirements. Building owners may need to meet insurance-provider criteria or environmentally focused guidelines. Furthermore, roofs frequently serve as platforms for amenity decks, rooftop equipment, roof anchors and solar-power systems.
The challenge is achieving owners’ program goals without compromising code compliance. Most jurisdictions require installed roof assemblies meet or exceed building code requirements, including minimum fire classification, drainage and overflow capacity, and wind-uplift pressure resistance, plus energy-conservation code requirements, including minimum R-value, air barriers meeting specified air permeance standards and typically reflective surfaces in Climate Zones 0-3.
The Next Chapter in Code Developments
Integrating building and energy-conservation code requirements is just the first step toward achieving resilient roof assemblies. As new information becomes available, everyone involved in the built environment must remain open to considering the latest practices, products and technologies. We should incorporate science-based minimum requirements into codes and standards, properly referenced to relevant I-Code sections.
These improvements to model codes have another profound benefit. Because model codes are the starting point for most jurisdictions, improved language, pointers and flexibility will be distributed to all jurisdictions through the adoption process. Jurisdictions won’t have to find balance in their codes; the balance will come to them, and better, more resilient roof assemblies will be the result.