When inputting Underground Walls, the CBECC Res engine will only allow a wall construction assembly which is either Concrete, Insulated Concrete Form (ICF) or Brick. For Underground Walls, you must select a construction assembly from the library which is one of these types, you cannot use conventional frame walls, and CMU walls are also not supported currently.
In the Building Tree, you must either select a different construction assembly that fits this description, or edit the construction assembly you have selected, hit the green Import button and import either a Concrete, ICF or Brick wall from the JA4 selections.
It is acceptable to add framing and insulation to the concrete wall once selected, however, in the Res T24 Perf tab.
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