IECC 2024 Section R408: Additional Efficiency Requirements Explained

Modified on Thu, 20 Mar at 12:37 PM

Introduction

IECC 2024 has introduced significant changes to the Additional Efficiency Requirements section, R408. Notably, these requirements are now an integral part of the Prescriptive Path, emphasizing the importance of energy efficiency in residential buildings. This article aims to provide a clear understanding of how these requirements are implemented in Ekotrope RATER QA checks with a general rationale behind the complex logic employed in certain subsections.

IECC 2024 Prescriptive Path requires that

Residential buildings must earn at least 10 credits from at least two measures listed in Table R408.2 to comply with Section R401.2.1.
An additional five credits are required for dwelling units with more than 5,000 square feet of living space located above grade.

Implementation Summary

Additional Efficiency Option	What’s included in our checks?	Notes
[R408.2.1] Enhanced building thermal envelope options	Checks for R408.2.1.1, R408.2.1.2, and R408.2.1.4 are included.	Roof solar reflectance index is not supported in Ekotrope RATER and hence is excluded from the credit calculations
[R408.2.2] More efficient HVAC equipment performance options	All of the measures specified in R408.2.2 are included	If home has a heat pump meeting measures 13 or 14, the rater must ensure that the heat pump is meeting the required capacity ratios. If not, one should subtract the earned credits from such measures. To earn credits, heat pumps and air conditioners must be rated in HSPF2, SEER2, and EER2 where appropriate.
[R408.2.3] Reduced energy use in service water-heating options	Checks for R408.2.3(1) through (5) are included.	Ekotrope RATER does not support modeling commercial heat pump water heaters rated in COP or SUEF rating for solar water heaters. Hence, R408.2.3(6) and (7) are excluded. To indicate compliance with R408.2.3.1, we’ve added a checkbox in the “Codes & Programs” section. To earn credits, manually check that the hot water distribution system meets the criteria.
[R408.2.4] More efficient thermal distribution system options	All measures are checked.	Please review the “Interpretation from ICC for R408.2.4” section for more details.
[R408.2.5] Improved air sealing and efficient ventilation system options	All measures are checked.	Where the home meets measures requiring a recovery ventilator, the rater must ensure that sensible and/or latent recovery efficiency is met as specified in R408.2.5, and the home in Climate Zone 8 does not use recirculation as a defrost strategy.
[R408.2.6] Energy efficient appliances	All measures are checked.	EnergyGuide label entries as provided in Ekotrope RATER are compared against required values as per Table R408.2.6.
[R408.2.7] Renewable energy	All measures are checked.	-
[R408.2.8] Demand response	All measures are checked.	If a smart thermostat is installed in the home, it is assumed that it meets the requirements specified in R408.2.8. Rater must ensure that they’re met; otherwise, subtract the credits earned from this section.
[R408.2.9] Opaque walls	Total TC compliance section will now use the maximum U-factor of 0.06 for wood-framed walls in the reference TC calculation for homes in climate zones 4 and 5, if one of the requirements is met.	-
[R408.2.10] Whole-home lighting control [R408.2.11] Higher efficacy lighting	All measures are checked.	We’ve added checkboxes for raters to indicate that the home is meeting requirements specified in respective sections to earn credits.

Interpretation from ICC for R408.2.4

The intent of Section R408.2.4 is that the energy used to heat or cool a space is efficiently used in the space intended to be heated or cooled by minimizing the losses outside the space.
The intent of Item 1 of Section R408.2.4 is to apply to buildings where the ductless systems and hydronic systems are located entirely within conditioned space and where duct systems are not provided within the building.
If ductwork is utilized anywhere within a Residential Building, Item 1 of Section R408.2.4 is not applicable, but any of the Items 2, 3, or 4 that are applicable in such a building may be applied to the credit score for the building in accordance with Section R102.1. Section R102.1 states that if there is a conflict between two provisions of the code, the more restrictive applies. As such, if a building gets less credit for one of the ductwork criteria of Section R408.2.4, that credit would be applicable because it would be the most restrictive (the one that provides the lowest score).

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