Our project is pursuing LEED BD+C for Healthcare v4. Under the Minimum Energy Performance prereq, it is stated that the building must comply with the mandatory provisions of ASHRAE 90.1 2010. In this project we have radiant slab heating on the upper levels of the building and not in floors at- or below-grade.

One of the mandatory provisions in ASHRAE 90.1 2010, Radiant Floor Heating, states that "the bottom surfaces of floor structures incorporating radiant heating shall be insulated with a minimum of R-3.5. Adjacent building envelope insulation counts towards this requirement". According to the ASHRAE section, 3.2 Definitions, "floor, envelope" is defined as the "lower portion of the building envelope, including opaque area and fenestration, that has conditioned or semiheated space above and is horizontal or tilted at an angle of less than 60 degrees from horizontal but excluding slab-on-grade floors." We believe the explicit use of “building envelope” excludes raised floors, as they are not considered envelope. If referring to ASHRAE building envelope requirements of the Chapter 5, 5.5 tables series on Building Envelope Requirements by Climate Zone, the distinction between “heated” and “unheated” only appears under the category slab-on-grade and not under raised floors.

We interpret this to mean that we do NOT need to insulate the radiant slabs on the upper levels. As this is a mandatory requirement, we want to make sure we have interpreted this correctly and confirm that upper level floors, receiving radiant heating within the slabs do not need to be insulated for compliance with the LEED Minimum  Energy Performance prerequisite. Can this be confirmed/interpreted?

On a related note, our interpretation of Title 24, Part 6 Energy Code (to which this project will comply) defines a “heated slab floor” as either on-grade, raised, or a lightweight concrete slab topping. And there are insulation requirements for heated slab floors on- or below-grade, but the Code does not explicitly require insulation on raised slabs. We think ASHRAE and Title 24 are in agreement here.