27 Apr Paths to comply with residential energy efficiency requirements
Codes Corner with: Lynn Madden, Hallmark Homes, IBA Codes & Safety Committee Chair & Nate Kleist, Energy Diagnostics
As a quality inspector for a custom home builder, I know firsthand how difficult it can be to make sense of some of the requirements in the 2020 Indiana Residential Code (InRC). Outside of safety related code questions, one of the areas of the code that has caused some of the greatest confusion in the field for builders, trade contractors, and inspectors is energy efficiency, in part, because of the options you’re given to demonstrate compliance. I reached out to IBA member Nate Kleist, Director of Operations at Energy Diagnostics, for information. Nate is an active member of IBA’s Codes & Safety Committee and has provided information on cost-effective ways to achieve compliance with the residential energy efficiency requirements.
Q: Where are the energy efficiency requirements for new home construction found?
A:Chapter 11 of the 2020 InRC provides the energy efficiency requirements for new home construction and offers 3 paths for compliance – prescriptive, simulated performance, and energy rating index.
Q: How do the paths for compliance differ?
A: Prescriptive Path –requires both “mandatory” AND “prescriptive” code items to be met ; limited trade-offs allowed
The prescriptive compliance path requires no software or modeling and is verified via a checklist. Within this path, there is the optional total UA (sum of U-factor times assembly area) alternative which allows for envelope tradeoffs, but none for mechanicals or performance testing. Compliance may be calculated through RESCheck and the maximum UA must be greater than or equal to the proposed design UA to demonstrate compliance.
Simulated Performance Path – allows trade-offs through good testing results and increased R/U values, but not for upgraded, high efficient equipment
The simulated performance path provides greater flexibility through using computer simulation to demonstrate that the proposed design would have the same or less than the same energy as the “standard reference design” building. The proposed design must include all requirements labeled “mandatory” in the code. Compliance calculations must be performed using energy modeling software which does require blower testing along with the mandatory duct testing that’s performed post-construction to measure leakage to outside.
Energy Rating Index (ERI) – requires that the rated design have an ERI less than or equal to 62 (Climate Zone 4) or 61 (Climate Zone 5) when compared to the ERI reference design; allows credit for installing high efficient mechanical equipment
ERI is calculated by comparing a residential building to the standard reference design and requires that modeling and testing must be done by a third party. This path allows builders to get credit for installing high efficient mechanical equipment. There is, however, a backstop that is built into this path in which the building thermal envelope must be greater than or equal to the levels of efficiency and SHGC in the prescriptive Table 402.1.1 or 402.1.3 in the 2009 IECC. Since IN amended their prescriptive table to match that of the 2009 IECC, this greatly limits the trade off potential of this path.
Q: How has Energy Diagnostics assisted builders in complying with the simulated performance path?
A: When taking advantage of the simulated performance path, the home being analyzed starts with a reference home that is based off the current code’s prescriptive requirements. To achieve compliance through this code path, all items listed as mandatory in the chapter must be completed and then the overall heating and cooling usage must be equal to or less than the reference home. This can be achieved in many different ways, which is why this is the most flexible path, allowing the builder and homebuyer to save money on construction costs but still have a finished product that is as efficient if not more efficient than a home that follows the prescriptive path.
Q: Under the simulated performance path where modeling is used, is it possible to achieve code compliance with less insulation and better air sealing of the envelope and ducts?
A: Yes, under the simulated performance path it is possible to achieve code compliance in homes with insulation levels that are less than the prescriptive table requirements. For example, you could go with 2×4 framing, osb sheathing and R13 for the walls provided the ducts are sealed and there’s little envelope leakage. Another option, if the test results were not good enough to fully cover the tradeoff, would be to add additional insulation somewhere else like an R45 in the attic vs the prescriptive R38
Q: Given the record-high lumber prices, which have nearly tripled since last spring, could using the simulated performance path save on framing?
A: Yes, the savings on framing and insulation material greatly outweighs the cost of the additional air sealing and performance report generation, saving the builder and home buyer money on the front end without sacrificing efficiency on the back end and this is due to the tradeoff being made.
Q: Are there other advantages to using simulated performance path?
A: Yes, another advantage of using the performance path is that an Energy Specialist or HERS Rater is involved in the project from the early design and permitting process to final testing once the home is built to help guide the builder through the energy code compliance process, acting as a third party verifier on the jobsite. In the end, if you are looking for some design flexibility, the opportunity to save on construction costs and professional guidance to meet the requirements of the InRC, then the performance path is for you!