Exceed code minimums for wall insulation

Although they’re theoretical, whole-wall R-values are closer to real life insulating values.
Consider a 2x4-in. wall framed 16-in. O.C. and stuffed with high-density R-13 fiberglass batts. Assuming a perfect installation, its whole-wall insulation value is closer to R-10 (25% to 30% less) due to thermal bridgingHeat flow that occurs across more conductive components in an otherwise well-insulated material, resulting in disproportionately significant heat loss. For example, steel studs in an insulated wall dramatically reduce the overall energy performance of the wall, because of thermal bridging through the steel. caused by wall studs, plates, and the band joist. This problem is particularly acute with steel framing. And, more difficult to measure, the true insulation value likely is even less because of poor installation, air infiltration, wind wash, air-convection loops, etc.

The solution: More is better. Here’s an example: Build a 2x6-in. wall, 24 in. O.C. with R-19 fiberglass between the studs. Add a 2-in. layer of XPSExtruded polystyrene. Highly insulating, water-resistant rigid foam insulation that is widely used above and below grade, such as on exterior walls and underneath concrete floor slabs. In North America, XPS is made with ozone-depleting HCFC-142b. XPS has higher density and R-value and lower vapor permeability than EPS rigid insulation. to the exterior–seams taped. This combination gets you to a little over R-25, which is acceptable in climate zone 5&6.

Whole-wall values should be used in computing loads and energy usage. Actually calculating them requires some training or use of a program that can factor in framing percentages.

Target whole-wall insulation values
Zones 1-4: R-19
Zones 5&6: R-25
Zones 7&8: R-30

Green points

LEED for HomesLeadership in Energy and Environmental Design. LEED for Homes is the residential green building program from the United States Green Building Council (USGBC). While this program is primarily designed for and applicable to new home projects, major gut rehabs can qualify. : Meeting Energy StarLabeling system sponsored by the Environmental Protection Agency and the US Department of Energy for labeling the most energy-efficient products on the market; applies to a wide range of products, from computers and office equipment to refrigerators and air conditioners. requirements is a prerequisite; 2 points for installing enhanced insulation that exceeds the International Energy Conservation Code by at least 5% (EA 2).
NGBSNational Green Building Standard Based on the NAHB Model Green Home Building Guidelines and passed through ANSI. This standard can be applied to both new homes, remodeling projects, and additions. /ICC-700: Up to 15 points for meeting various insulation installation guidelines (703, prescriptive path) plus additional points third-party verification and air sealing (703.2)

Learn more in the Green Building Encyclopedia:

Walls Must Be Durable, Well-Insulated, and Weather-Resistant

Further Resources

Building Science Corp.
RR-0903: Building America Special Research Project—High-R Walls Case Study Analysis