Part 4—Ratings Systems

MOISTURE MANAGEMENT IN GREEN BUILDING RATING SYSTEMS

For the moisture durability assessment, the four most common green building rating systems available for new construction projects are compared against the six construction phase categories as shown in Figure 6. The green building rating systems reviewed are:

• Leadership in Energy & Environmental Design (LEED®), version 4.1¹³
  Note: LEED® is a registered trademark of the U.S. Green Building Council.
• Green Globes®, version 2019⁶
  Note: Green Globes® is a registered trademark of Green Building Initiative, Inc.
• Living Building Challenge (LBC™), version 4.0¹⁰
  Note: LBC™ is a registered trademark of International Living Future Institute.
• 2018 International Green Construction Code (IgCC®)⁸
  Note: IgCC® is a registered trademark of International Code Council, Inc.

Figure 6. Green building rating systems moisture durability assessment.

SUMMARY OF GREEN RATING SYSTEM ASSESSMENT

Compiled across the typical project life-cycle phases, below is a summary of the notable factors that apply to moisture assessments across the highlighted green building rating systems:

Material Selection

In terms of material selection, there is some consistency across all four rating systems. Starting with above-code specifications in the top row of Figure 5, all four are shown in yellow or “partially or indirectly addressed.” This is because all four have requirements for improved energy efficiency over the code minimum, including light colored or reflective roofing. The enclosure is generally above the code minimum, but there aren’t direct above-code measures related to moisture durability mitigation. None of the four rating systems have measures that encourage comprehensively sourced products to mitigate future risks within and across enclosure systems. Though none are specific to material moisture certifications, all four systems do provide a mechanism to reward products for third-party certifications; these are shown in blue in the last row, indicating this element is clearly “addressed” in the green standards.

Design & Procurement

The design phase is where the specifications can enable success mitigating moisture throughout the later project phases and helping align with the OPR. A number of items in this phase are “partially or indirectly addressed” by both LEED v4.1 and Green Globes through the enclosure commissioning credits; see additional discussion in the commissioning section below. In the Green Globes column, the rating system addresses system performance by providing credit for performing a Building Risk Assessment of the design to resist extreme events. Green Globes also touches on moisture control design analysis, but the credit is focused on managing interior generated moisture, and indirectly includes building enclosure components as part of an ASHRAE Standard 160 moisture analysis when interior moisture is expected. The 2018 IgCC addresses moisture control design analysis directly by requiring all designs to perform dynamic heat and moisture analysis, including ASHRAE 160, of the enclosure and across interior space conditions. The Living Building Challenge, as a rating system, doesn't provide specific or prescriptive moisture mitigation requirements for many aspects of the design and procurement process.

Construction Activities

The construction phase is a period of the building’s life that is often not designed to manage moisture and can lead to a reduced life-cycle if it is not performed well. All green rating programs, except for the Living Building Challenge, include measures to address temporary moisture protection during construction. None of the rating systems have minimum substrate acceptance to provide “stoplight conditions” for enclosure installations, such as moisture on the roof deck. The project specifications and the various construction trades are left to manage these acceptance handoffs. Notably, Green Globes provides direct measures for onsite quality assurance and verification, while LEED v4.1 indirectly captures this scope in its enhanced enclosure commissioning credit. The previous version of Green Globes also included the RRO program by reference but is now described generally as elements of a third-party observations verification program.

Performance Testing

The IgCC is the only one of the four green rating systems to directly address field performance testing by providing enhanced guidance on whole building air tightness testing. The comprehensive testing of the built enclosure can have broad performance impacts on achieving the intended energy efficiency from the design to the field, mitigating ongoing moisture accumulation due to air leakage condensation, and enabling the HVAC design to deliver a comfortable space to the occupants. LEED v4.1 and Green Globes do not include specific measures for performance testing, but they can be a part of the Enhanced Commissioning Credit of the Building Enclosure; see additional discussion in the commission section below. By not identifying scope in the LEED and Green Globes enclosure commissioning credits and minimum performance requirements, field testing can lead to a lot of variation in actual, built outcomes. For this reason, both rating systems are shown as “partially or indirectly addressed.” The Living Building Challenge, as a rating system, doesn't provide specific or prescriptive requirements for performance testing.

Operation & Maintenance

LEED v4.1 includes occupant training directly in the Enhanced Commissioning Credit for the Building Enclosure, but the inclusion of future assessments and specifically addressing manufacturer system documentation is left up to the project team. Green Globes provides additional points for evaluating the building’s “operational continuity” or a “recovery assessment” in the event of extreme weather conditions. Green Globes also provides specific credit for enclosure systems training in the use-phase, and similar to LEED, yet manufacturer system documentation is left up to the project team. The IgCC includes requirements for a detailed Service Life Plan (10.3.2.3), which includes documenting, planning, and providing access to the enclosure elements based on their expected service life. It does not, however, deal with future-use assessments nor specific service, warranty, or guarantee documents of the building enclosure. The Living Building Challenge, as a rating system, doesn't provide specific or prescriptive requirements for the operations and maintenance of the building’s use-phase.

Building Enclosure Commissioning

Both LEED v4.1 and Green Globes provide additional points for enclosure commissioning. It is important to clarify that even though points are being given for enclosure commissioning, there are very few minimum tasks for project teams to accomplish. The decisions about many critical moisture durability aspects are left up to the project team to decide how to proceed. A notable improvement in LEED v4.1 provides additional guidance over the older LEED 4.0 by now referencing ASTM E2947 Standard Guide for Building Enclosure Commissioning.⁵ This standard provides an exhaustive list of optional performance tests. It’s incumbent upon the designer to establish a minimum scope to vet out project performance and achieve credit for the Enhanced Commissioning Credit. The Living Building Challenge and IgCC do not include requirements or credits to include enclosure commissioning in the rating systems. The IgCC does have a commissioning requirements section, but unfortunately, the building enclosure is not included in the list of “Systems to be Commissioned” (IgCC 10.3.1.2.1).

Figure 7. Green building rating systems moisture durability summary.

Figure 7 summarizes each of the six individual detailed assessments reviewed across the project life-cycle phases. There is quite a range of results across the green building rating systems assessed.