This is of significance to structural engineers in Washington because the 2009 Washington State Energy Code dictates the prescriptive details of insulation at foundation walls:
From a chapter relating to the "Washington State Single-Family Residential Energy Code"
502.1.4.8 Slab-On-Grade: Slab-on-grade insulation shall be placed on the outside of the foundation or on the inside of the foundation wall. The insulation shall extend downward from the top of the slab for a minimum distance of 24 inches or downward to at least the bottom of the slab and then horizontally to the interior or exterior for the total distance of 24 inches. Above grade insulation shall be protected. A 2-inch by 2-inch (maximum) nailer may be placed at the finished floor elevation for attachment of interior finish materials.From a chapter relating to the "Washington State Nonresidential Energy Code"
1311.5 Slab-On-Grade Floor: Slab-on-grade insulation installed inside the foundation wall shall extend downward from the top of the slab a minimum distance of twenty-four inches or to the top of the footing, whichever is less. Insulation installed outside the foundation shall extend downward a minimum of twenty-four inches or to the frostline, whichever is greater. Above grade insulation shall be protected.What does this mean for below-grade walls that require a firm, monolithic slab to resist lateral earth pressures? Perhaps a lot of back-and-forth in future project meetings.
EXCEPTION: For monolithic slabs, the insulation shall extend downward from the top of the slab to the bottom of the footing.
