Replies

1. GBA Editor
   Martin Holladay | May 23, 2019 03:50pm | #1

   Colby,
   No (unless you are planning on installed PEX tubing in the slab for a hydronic heating system).

   For more information, see this article: "Determining Sub-Slab Rigid Foam Thickness."

2. Expert Member
   Dana Dorsett | May 23, 2019 05:13pm | #2

   Code doesn't demand it, but in humid Zone 3A there may be a rationale for 1-1.5" of EPS under the slab to keep "musty basement smell" at bay during the humid summer when the slab temp could otherwise be well below the ventilation air's dew point, and could still have a lifecycle rationale on energy costs. See Table 2, p.10:

   https://buildingscience.com/sites/default/files/migrate/pdf/BA-1005_High%20R-Value_Walls_Case_Study.pdf