Building For the Future Part II: 2018 IECC Building Envelope Updates
In Part I of our Building for the Future blog post we gave an overview of the 2018 IECC update and long-term effects, estimated cost and energy savings Nebraska is expected to see.
Now let’s dive in a little deeper to understand the 2018 IECC code changes that lie ahead and its effects on the building envelope, which is the design and construction of the exterior of the building. A good building envelope involves using exterior wall materials and designs that are climate-appropriate, structurally sound and aesthetically pleasing.
The building envelope includes:
- Roof
- Sub Floor
- Exterior Doors
- Windows
- Exterior Walls
2018 IECC and All-Glass Buildings
Glass has become a go-to material for architects and owners when it comes to new commercial buildings. Many are going with an all-glass design, allowing the daylight to flow inside and relying less on overhead lighting. However, using glass can have a major impact on a building’s energy performance.
Under the 2018 IECC prescriptive pathway Section, C402.4 Fenestration (Prescriptive) subsection C402.4.1 Maximum area says that “vertical fenestration area, not including opaque doors and opaque spandrel panels, shall be not greater than 30% of the gross above-grade wall area.”
However, Section C402.4.1.1 Maximum area allows for the percentage to increase to 40% provided the building is located in Climate Zones 1 through 6 and the following requirements are met:
- In buildings, two stories or less a minimum of 50% of the net floor area is located in the daylight zone.
- In buildings, three stories or higher a minimum of 25% of the net floor area is located in the daylight zone.
- Daylight responsive controls that comply with Section C405.2.3.1 are installed in the daylight zones.
- Visible transmittance (VT) of the vertical fenestration is a minimum of 1.1 times the solar heat gain coefficient (SHGC).
Our Region
We have a limited pathway to 40% fenestration because we are in Climate Zone 5. If the building owner wants even more glass on their façade, architects will then have to refer to ASHRAE 90.1, a minimum standard of energy efficiency, or utilize the 2018 IECC Performance Pathway.
Table 1 below shows the current 2009 IECC and 2018 IECC requirements (and equivalent ASHRAE Standard 90.1 requirements, since this is a compliance pathway).
The 2018 IECC Performance pathway, provides a mechanism for exceeding 40% fenestration. Section C407, Total Building Performance, of the 2018 IECC does have a few mandatory requirements, and fortunately, section C402.4 is not one of them. So, there is a way to exceed 40% fenestration.
In addition to the mandatory requirements outlined in C407.2, buildings must comply with Section C407.3 Performance-based compliance, which requires that the proposed building (proposed design) be shown to have an annual energy cost that is less than or equal to the annual energy cost of the standard reference design.
2018 IECC and All Metal Pre-Engineered Buildings
Metal pre-engineered buildings will also see a large impact on the 2018 IECC code updates. Under the 2018 IECC prescriptive pathway C402.2 Specific building thermal envelope insulation requirements (Prescriptive) states:
- C402.2.1 Multiple layers of continuous insulation board - continuous insulation needs to have two layers with joints staggered.
- C402.2.2 Roof assembly - minimum thermal resistance (R-value) of the insulating material installed either between the roof framing or continuously on the roof assembly.
Historically, owners chose metal buildings because it is the most cost-effective way to build a structure. But the continuous insulation that is now required under the 2018 IECC will make it difficult for owners to make their metal buildings compliant and will force them to specify more expensive materials. It’s possible that at some point a more conventional building would be a more cost-effective option.
Schemmer’s Dan Kerns, AIA, Commercial Market Leader, stated that the industry is starting to respond by making systems more compliant such as using continuous insulation.
Simple Saver System
The Simple Saver System is a continuous insulation option for metal buildings. It is high-performance insulation and finishing system designed for roof and walls in low rise commercial buildings, which uses a double layer of insulation to get a better R-value. The system will yield designed insulation values without excessive compression and voids, which are common with other methods of installation.
What Lies Ahead?
As meeting code becomes more complex, the compliance path is recommended most often, which is the prescriptive approach. Per the U.S. Department of Energy, the prescriptive approach includes, “requirements that either must be met by every building design or if the requirement is not met, a tradeoff must be made to ‘make up’ for not meeting that requirement.” In other words, you must meet all U-values of the roof, walls, foundation and fenestrations. If a tradeoff is indeed needed in the end, the quoted price has covered any changes.
Schemmer’s Dan Kerns, AIA, Commercial Market Leader on 2018 IECC
“Every jurisdiction will adopt these updates or with modifications, and ultimately it will come down to the sophistication of the municipality. Owner’s first costs have the potential to change based on the code updates,” stated Kerns.
Schemmer’s Michael Sinclair, AIA, and American Institute of Architects Nebraska Chapter President on 2018 IECC
“Several municipalities are utilizing the assistance of third party consultants to navigate and sort through the significant changes that this version brings with it. Proposed amendments and enforcement issues are all valid concerns for the local Authorities Having Jurisdiction (AHJs). However, despite the perceived challenges and restrictions, there are a handful of proactive recommendations that are forward-thinking and exciting for us as designers. New skylight requirements and solar-ready zones (as spelled out in Appendix CA) set the stage for future investment in renewable and sustainable energy systems,” said Schemmer's Michael Sinclair, AIA, and American Institute of Architects Nebraska Chapter President.
Stay tuned for our next blog in this series to learn more about 2018 IECC and how it will effect the mechanical systems.
Design with Purpose. Build with Confidence.
Schemmer is a full-service architecture, engineering and construction field services consultant. Providing responsible solutions for complex design and construction-related challenges.
Founded in 1959, we are grounded in our past but remain fully committed to the future. Located in three States and six offices throughout the Midwest. Schemmer is providing services to clients from coast-to-coast and border-to-border across the United States.
Schemmer's services include:
- Architecture
- Structural
- Mechanical
- Electrical
- Site/Civil
- Transportation
- Water/Wastewater
- Survey
- Geotech
- Field Services
Sources: Graboyes Commercial Window and Glass Solutions; ICC Digital Codes Library; Thermal Design; General Insulation Company; and Star Building Systems
