IECC 2021 and the City of Louisville’s Adoption

Date Published: March 1, 2022

City of Louisville adopts IECC 2021 and its Net Zero Appendix

The latest and most challenging energy codes have been released by the International Code Council and their IECC 2021 codes.  While the vast majority of Colorado’s Cities and Counties have adopted one iteration of the IECC or another, ranging from IECC 2009 to IECC 2018, the City of Louisville took the plunge and adopted the IECC 2021 in November of this past year in addition to a net zero appendix.

Like the IECC codes that came before it, the 2021 iteration of the code allows for several pathways for compliance including a performance pathway, but we’d like to focus on the prescriptive pathway for the purposes of this article.

The IECC 2021 prescriptive pathway through the code includes increased insulation levels throughout the building to ensure a very high performing thermal envelope.

Under this code, attic insulation levels are now required to achieve R-60, while above-grade walls assemblies are given one of four options: either R-30 in the cavity with no continuous exterior requirement; R-20 with an R-5 continuous insulation;  an R-13 with an R-10 continuous insulation; or no cavity insulation but an R-20 continuous.

The IECC 2021 also adds a requirement for an “additional efficiency package” to be selected from a list (found in R408). The code makes efforts to define air sealing requirements, but blower door testing requirements do not change from 3 ACH for climate zone 5.

IECC 2021

Code Picture for Climate Zone 5

Under the IECC 2021, duct leakage testing becomes mandatory for all duct systems regardless of whether they are completely within the thermal envelope.  Duct leakage tests that are entirely within the envelope are allowed up to 8% leakage, while systems that are partially outside of the envelope will be required to achieve 4% or lower.

The IECC 2021 prescriptive code does not require balanced mechanical ventilation for climate zone 5, but does introduce water piping insulation requirements.

IECC 2021

So what did Louisville adopt exactly?

In addition to adopting the IECC 2021 energy code, the City of Louisville adopted “Appendix RC Zero Energy Residential Building Provisions”  This relatively small addition to the energy code introduces quite a substantial change for new home builds in Louisville.

Any new construction projects will be required to achieve a net zero score with an energy rating index (HERS rating). This alone might be considered quite a step up in the code, but the somewhat obscure requirement that these houses must first achieve a score of 47, before any renewables, represents a monumental shift in building design.

Achieving these sub 50 scores for new construction homes will require much more than even the IECC 2021 code mandates.  Preliminary models on concept homes that we have built to explore these upgrade options suggest that compliance with this code will be possible only with very tight (less than 1 ACH) envelopes, minimal glazing areas, and even the possibility of geo thermal heating and cooling system requirements.

Other IECC 2021 Adoption

The 2021 IECC energy code will be adopted more in Colorado.  Other areas that have adopted it already include Larimer County.  Denver and other municipalities are reviewing the 2021 codes.

The increased insulation levels, particularly in the ceiling and attic, along with the mandatory duct leakage testing requirements will make compliance with the 2021 IECC more difficult in Colorado.  The results will continue to be increased energy efficiency in new construction homes.

Scott Home Inspection has been offering energy code compliance services to architects and builders in Colorado for over 15 years.  Especially with the introduction of COBECC 2020 (the City of Boulder’s latest energy code which also has net zero requirements) we have a great deal of understanding for which features and specifications will be needed in a home to achieve compliance no matter the area that your home is being built.  We would be glad to have a conversation about your project!

More Information:

Marshall Fire Updates

IECC 2021 Standard

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About the Author: Joe Ophoff

Joe Ophoff has been working as an energy efficiency specialist since 2014. He is the Energy Services Manager at Scott Home Inspection in Colorado.

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