This week I want to shift gears and talk about residential building envelope code compliance in accordance with the 2015 IECC.
The 2015 IECC offers three methods for building envelope code compliance: the prescriptive requirements, the performance method and the energy rating index method.
The prescriptive requirements are the code minimums that are documented in the building code. These are the specific requirements, most often broken down by climate zone.
When you apply a specific R-value or U-value, like putting R-20 in a wall in Climate Zone 5, you are simply meeting the prescriptive code requirement.
Essentially, you can meet code by following the black and white letter of the code and using the minimum values specified by the code. This is the prescriptive method.
The performance method allows you to use simulated energy performance to show that the proposed design has an annual energy cost that is less than or equal to the annual energy cost of the standard reference design, or the 2015 prescriptive minimum.
The most common method to document performance-based compliance is with the use of energy analysis software.
Finally, the Energy Rating Index, or ERI, is a calculated number on an index scale of 0 to 100, which compares the proposed design to an ERI reference building built to the minimum requirements of the 2006 International Energy Conservation Code.
The Energy Rating Index requirement ranges from 51 to 55, which means that the proposed design must outperform the ERI reference building by 45% to 49%, depending on climate zone.
The most common method of code compliance is the prescriptive method, but there is often more design flexibility using the other compliance options, especially when using a high-performance material like spray foam insulation.
Stay tuned because over the next few weeks we will dive into some specifics behind each of these compliance options for building envelope code compliance.