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Using FPIS ci provides one of the most effective means insulating buildings to comply with the energy code because it insulates the entire structure to minimize thermal bridging of framing materials. FPIS ci also provides one of the more robust means of satisfying the moisture control requirements of the building code (refer to STEP 3). Depending on your climate, FPIS ci may be required if using the prescriptive compliance path (e.g., the simple R-value compliance method). However, the amount of FPIS ci can be adjusted as needed using other compliance paths in the energy code or this calculator tool.

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Alternatively, use the prescriptive wood-frame wall R-value recommendations below based on the 2024 edition of the International Energy Conservation Code (IECC) and your climate zone as shown in the map below. 

The FPIS material R-value specified and the FPIS material type selected (e.g., XPS, EPS, or PIC) will affect the thickness of the continuous insulation layer on the exterior of the wall. This thickness may affect other construction details, such as cladding connections (see STEP 4 later).

NOTE: To address energy code whole building air leakage and air barrier requirements, refer to STEP 3 for coordination with water, vapor, and air control strategies.

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Overview

1. Determine your Climate Zone (see Figure 1 or Chapter 3 of the IECC [RE])
2. For the R-value recommendations, refer to Table 1 below, the locally adopted energy code, the IECC, or ASHRAE 90.1 as appropriate.
3. For the prescriptive U-factor method to determine alternative R-value solutions for compliance, refer to the Wood Frame Wall Calculator.
4. For the Performance or Energy Rating Index compliance methods, refer to an energy modeling or energy rating professional to determine compliance.