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, etc.
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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