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Moisture Durability, Roofing and Green Standards

A review of changes in codes, examples of roof and vertical assembly integrations, and tools to assess potential moisture challenges. 

By Benjamin Meyer, AIA, NCARB, LEED AP




Sponsored by:

Learning Objectives:

After reading this article, you should be able to: 

  1. Apply recent changes in energy codes to building enclosure roof and wall assemblies for improved energy efficiency.

  2. Evaluate effectiveness in existing green standards for a project’s long-term moisture durability regarding the scope and impact to the building enclosure.

  3. Identify how to utilize and supplement various green standards across the various project phases, including design and material selection, construction-related activities, field performance testing, and Building Enclosure Commissioning (BECx).

  4. Apply examples of best practices and tools to assist in designing energy-efficient and durable roofing and building enclosures.

PART 1—CONTEXT 

Recent changes in building model energy codes include envelope criteria that minimize building enclosure thermal loads and, in turn, reduce a building’s energy consumption. These changes require modifications in traditional building enclosure designs to meet evolving energy code requirements. Unfortunately, some energy-efficient designs, while code compliant, may adversely impact a building’s durability. 

The minimum requirements in green standards alone, such as LEED, Green Globes, and IgCC may lack comprehensive measures to ensure long-term durability of the enclosure assemblies. Optional and required credits included in green standards are beginning to address moisture durability and, in this article, are compared regarding the scope and impact of the building enclosure, across the project phases:

  • Material Selection 

  • Design & Procurement 

  • Construction Activities 

  • Performance Testing

  • Operation & Maintenance

  • Enclosure Commissioning


This article reviews various aspects among the green standards including gaps and similarities in the rating systems, and strategies to utilize the best parts of each rating system to improve project performance related to moisture durability. Detailed roof system examples will also be provided, demonstrating how these measures can enable energy-efficient AND durable enclosure assemblies. 


Greenbuilding

There can be a perception in the market that a “green building” is a better building, and that the risks associated with “building differently” are inherently covered by the green certifications driving the industry forward from a sustainability standpoint. Both better buildings and risk mitigation can be accomplished through building green, and this article will discuss some of the key principles to accomplish this for building enclosures and roof assemblies. 

Moisture durability of enclosure systems focuses on the interaction of the materials, assemblies, and their design configurations in the building. The goals of managing moisture durability are to establish performance expectations, allow enclosures to perform as intended as well as continue to perform through the project lifecycle, and be serviced or maintained in a way that minimizes risk of damage to the enclosure and performance of other critical building systems. This discussion focuses on the moisture durability aspects of buildings and how they relate to energy performance and lifecycle expectations. While other aspects of resilience are also important, moisture durability targets risks that are not necessarily related to climate change, yet are related to the design of enclosure and roof assemblies directly. 


Moisture Durability in Context

The American Institute of Architects (AIA) defines resilience2 as “mitigating risk for hazards, shocks, and stresses and adapting to changing conditions.” Resilience goes beyond the minimum code requirements to address issues that influence long-term performance. The “hazards, shocks and stressors” can come from external sources as well as from the design decisions of the built environment. Some external sources can be extreme events such as tornadoes and wildfires, and some are common and persistent adverse events from design decisions, resulting in moisture risks in the building enclosure. This perspective of moisture durability as a risk fits within many existing terms and goals that stem from sustainability, resilience, adaptability and mitigation initiatives; moisture durability fits within these goals and is not separate from them, as demonstrated in Figure 1. 


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Figure 1 - Moisture durability and energy efficiency are part of resilient design.





Figure 2 - Increasing efficiency requirements are compounded by green rating systems.3, 7,






Figure 3 - Energy efficiency improvements can lead to increased moisture risks in a building enclosure.






" The minimum requirements in green standards alone may lack comprehensive measures to ensure long-term durability of the enclosure assemblies... "

PART 2—COMPLEXITY 

Energy Efficiency is a Moving Target

The minimum or baseline energy efficiency in the code requirements and owner’s performance expectations have been a moving target over time. The cost-effective and validated energy savings has increased in each of ANSI/ASHRAE/IES Standard 90.1 (ASHRAE 90.1) three-year publications, which is one of the underlying national energy standards.3 The ASHRAE 90.1—2019 version was validated by the Pacific Northwest National Laboratory as an additional 5 percent of savings over the previous 2016 version.17 

Compounding the energy savings, green building rating systems generally require additional savings beyond the baseline and provide points for exceeding the baseline. In addition, the energy performance requirements within green certification systems are also improving. As an example highlighted in Figure 2, the same energy savings that would have contributed 10 points to the LEED v3 rating system is roughly equivalent to the starting energy savings required in LEED v4.1, which is in the pilot phase13 at the time this article was published. Not every local jurisdiction adopts the same base model codes and standards at the same time and rate, which leads to additional confusion in the design and construction industry.


Interactive Complexity and Tight Coupling

The book Normal Accidents by Charles Perrow explains how significant technological advancement can lead to failures.16 Perrow describes two main components of “normal accidents.” The first component being “interactive complexity” as a function of the number and degree of system interrelationships; when this factor is high… surprises are to be expected. The second component is “tight coupling,” the degree at which initial failures can concatenate rapidly to bring down other parts of the system; the more highly-linked… surprises are not easily isolated and resolved. If a system has only one of the two components then it is still a risk, but is more easily managed. When “interactive complexity” and “tight coupling” are combined, accidents could be considered “normal” or expected according to Perrow. 

As more materials and additional requirements are added to enclosures, it is important to recognize when materials and assemblies need to change in order to achieve higher energy performance. In a broad sense, as energy efficiency is improved in building enclosures, moisture risks can increase from decreased heat flow across the assemblies, as shown in Figure 3. The changes in enclosures can manifest as generally lower exterior surface temperatures (during heating months) as the exterior is less dependent on the interior space conditioning. As we improve energy efficiency, we may also be increasing moisture risks in building enclosures. And the increased risk of “normal accidents” may result from more complex designs that are more tightly coupled to the building’s HVAC operations, structural elements and occupant-use conditions. 

Consider the following real-world example of the “normal accidents” concept in practice and how it relates to a client’s awareness of or willingness to accept this risk for an innovative building. This relevant example comes from the first-ever LEED platinum building and a recently closed legal case.14 The example demonstrates the building enclosure’s technical complexity and tight coupling across various building systems. In the court’s findings, the decision lays out the framework mirrored in Normal Accidents stating “the inappropriate use of Parallams as structural support without proper weather protection”—it’s a complex system—and “these beams would have failed… well before they got around to doing any remedial measures at all.”—the systems are tightly coupled. 

The concept of predictable outcomes from Perrow’s book makes sense in theory, but in practice, it can be complicated as this case demonstrates. Such case studies help bring awareness to potential issues and highlight the importance of establishing processes to manage the unanticipated moisture risks as early as possible. It is important through this green rating system assessment to recognize the options and limitations that exist with the rating systems and their actual coverage to mitigate moisture risks in the face of complexity and system coupling. 


Benjamin Meyer, AIA, LEED AP, is a Roofing & Building Science Architect with GAF. He can be visited at, https://www.linkedin.com/in/benjamin-meyer-728740a/


References

1. Air Barrier Association of America, Quality Assurance Program (QAP)
www.airbarrier.org/qap/, accessed September 2020.

2. American Institute of Architects, AIA Resilience and Adaptation Online Certificate Program
aiau.aia.org/aia-resilience-and-adaptation-online-certificate-program, accessed September 2020.

3. ANSI/ASHRAE/IES. Standard 90.1-2019, Energy Efficiency Standard for Buildings Except Low-Rise Residential Buildings. ANSI/IES/ASHRAE, 2019.

7. International Code Council. 2018 IECC - International Energy Conservation Code. International Code Council (ICC), November, 2017.

13. U.S. Green Building Council, Inc., LEED Credit Library, LEED BD+C: New Construction, Version 4.1. Washington DC: U.S. Green Building Council. Accessed September 2020.

14. Kaplow, Stuart, “Lawsuit over First LEED Platinum Building is Over,” Green Building Law Update,  www.greenbuildinglawupdate.com/2015/12/articles/leed/lawsuit-over-first-leed-platinum-building-is-over/
December 13, 2015, accessed September 2020.

16. Perrow, Charles. Normal Accidents: Living with High-Risk Technologies New York: Basic Books, 1984.

17. M. Rosenberg and J. Zhang, Ph.D. “Energy Savings Analysis of ANSI/ASHRAE/IES Standard 90.1-2019 Final Progress Indicator.” Pacific Northwest National Laboratory. Presented at ASHRAE SSPC 90.1 Winter Meeting in Orlando FL, February 2, 2020.

Building Enclosure | BuildingEnclosureOnline.com | Summer 2021

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