an excellent opportunity for thermal mass possibly benefiting from direct solar gain through south facing windows

the first floor of a building causing the numbering of floors in Britain to be one less than in the US. The US second floor is the first floor in Britain.

Any occupiable floor less than one story above or below grade with direct access to grade. A building or facility always has at least one ground floor and may have more than one ground floor as where a split level entrance has been provided or where a building is built into a hillside. 3.5.34

The floor of a building closest to the building grade.