What do four green building rating systems do to manage moisture durability? (1 LU|HSW)

In part of its 1.0LU/HSW course, AIA partner GAF explores how green rating systems and guidelines address moisture management.

This article is part of a 1.0 LU | HSW course “Moisture Durability, Roofing, and Green Standards” that goes further into detail on the assessment of four green building rating systems. Click here to learn more about managing moisture risk in roofing design, and to earn credits through GAF and AIA Partner publication.

A building enclosure that is able to withstand the effects of moisture throughout its life-cycle is a crucial component of resilience, which mitigates risk for hazards and adapting to changing conditions[1]. Resilience goes beyond the minimum code requirements to address issues that influence long-term performance. Extreme events such as tornadoes and wildfires are known to cause damage, and yet some buildings incur preventable damage due to design decisions, weathering, and use, resulting in moisture risks in the building enclosure. A building enclosure that is able to manage moisture durability risks has an opportunity to incorporate improved energy efficiency, continuity of operations during extreme events, and a longer life span, yet needs to do so with careful consideration. Moisture durability has a key role to play, and enclosure systems are a good place to focus on the interaction of the materials, assemblies, and their design configurations in the building.

The book “Normal Accidents” by Charles Perrow explains how significant technological advancement can lead to failures[2]. 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 “interactive complexity” 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 “tightly coupled” 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.

To accomplish long-term durability, it’s recommended to manage moisture risks when interactive complexity and tight coupling are inherent in a roof and enclosure system design. As energy efficiency improves, moisture risks in building enclosures may also increase. And the increased risk shortened enclosure life-cycles may result from more complex designs that are more tightly coupled to the building’s HVAC operations, structural elements, and occupant-use conditions.

Increased energy performance and decreased heat flows can lead to increased moisture risks in a building enclosure.

For the moisture durability assessment, the four most common green building rating systems and standards available for new construction projects are compared against the six construction phase categories. They are:

• LEED version 4.1 [3]
• Green Globes version 2019  [4]
• Living Building Challenge, version 4.0  [5]
• 2018 International Green Construction Code (IgCC) [6]

Optional and required credits included in green standards are beginning to address moisture durability and are compared regarding the scope and impact of the building enclosure, across the project phases:

Moisture durability elements and assessment project life-cycle details.

Of the four green building rating systems, even when combined, none currently address moisture durability across all of the project life-cycle phases. It is recommended to use or borrow the best features from each green building rating system to shore up any project’s moisture management specifications, regardless of the actual green building certification being sought. The building enclosure commissioning (BECx) process, in addition to the green building rating systems, can help design the enclosure so that it performs across the project phases for long-term building performance.

Green building rating systems and standards moisture durability summary.

Click here to see the full article analyzing four green building rating systems, to learn more about managing moisture risk in roofing design, and to earn 1.0 HSW CEU credits through GAF and AIA Partner publication.

References:

1. American Institute of Architects, AIA Resilience and Adaptation Online Certificate Program, https://aiau.aia.org/aia-resilience-and-adaptation-online-certificate-program, accessed September 2020.
2. Perrow, Charles. Normal Accidents: Living with High-Risk Technologies New York: Basic Books, 1984.
3. 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.
4. Green Building Initiative, Inc. Green Globes® for New Construction 2019 Technical Reference Manual, Version 1.0, Green Building Initiative, Inc, December 2019.
5. International Living Future Institute, Living Building Challenge 4.0,  International Living Future Institute 2019.
6. International Code Council, Inc. and ASHRAE, 2018 International Green Construction Code powered by ANSI/ASHRAE/ICC/USGBC/IES 189.1-2017 Standard for the Design of High-Performance Green Buildings Except Low-Rise Residential Buildings. International Code Council, Inc. and ASHRAE, 2018.

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