IECC and Continuous Insulation

National model energy codes are advancing the way designers approach commercial and residential exterior walls, some by focusing on continuous insulation (CI) systems, which provide an uninterrupted insulation layer over an entire wall, not just in the wall cavities. The 2012 code has created more opportunities for the use of CI on both new residential and commercial walls. Any time the insulating layer is interrupted, the effective R-value of the insulation is reduced. Increases in thermal performance have resulted in CI figuring more and more in meeting both prescriptive requirements and overall building R-value targets.

Continuous insulation is not currently defined specifically in the ICC family of International Building Codes, but it is defined in ASHRAE 90.1 as:

Continuous insulation (c.i.): Insulation that is continuous across all structural members without thermal bridges other than fasteners and service openings. It is installed on the interior or exterior or is integral to any opaque surface of the building envelope.

Because CI combines rigid insulating foam and structural sheathing into an easily fabricated product that provides uninterrupted exterior insulation, air sealing, and a solid nailing surface for exterior finishes, many find it helps meet new code requirements in less time and with less incremental cost.

CI is found in various places in the 2012 IECC. Table C 402.2, for example, is a prescriptive table that lists all opaque (non-window) wall R-value requirements. Where CI is listed in this table, it is mandatory.

Footnotes are worth noting. In the commercial table, the footnotes specify: for SI: 1 inch = 25.4 mm. ci = Continuous insulation. NR = No requirement. In the residential table, the following footnotes are important to consider:

Footnote C. “15/19” means R-15 continuous insulation on the interior or exterior of the home or R-19 cavity insulation at the interior of the basement wall. “15/19” shall be permitted to be met with R-13 cavity insulation on the interior of the basement wall plus R-5 continuous insulation on the interior or exterior of the home. “10/13” means R-10 continuous insulation on the interior or exterior of the home or R-13 cavity insulation at the interior of the basement wall.

Footnote H. First value is cavity insulation, second is continuous insulation or insulated siding, so “13+5” means R-13 cavity insulation plus R-5 continuous insulation or insulated siding. If structural sheathing covers 40 percent or less of the exterior, continuous insulation R-value shall be permitted to be reduced by no more than R-3 in the locations where structural sheathing is used– to maintain a consistent total sheathing thickness.

The table pictured below is an R-value summary for the 2012 code. CI requirements are scattered throughout the table. Note that EPS (expanded polystyrene) R value = 3.8 /inch, while XPS (extruded polystyrene) R value = 5 /inch.

2012 IECC R-Value Summary

Energy performance criteria