R-value of walls is suppose to be R-22.
The way I am reading the following is that the basement is not conditioned space so the envelope would need to start at floor system of home or the basement area would need to be conditioned.
NII03.2 Ducts.
NII03.2.1 Insulation. Supply ducts in attics shall be insulated
to a minimum ofR-8. All other ducts shall be insulated
to a minimum of R-6.
Exception: Ducts or portions thereof located completely
inside the building thermal envelope.
BUILDING THERMAL ENVELOPE. The basement walls,
exterior walls, floor, roof and any other building element that
enclose conditioned spaces.
CONDITIONED SPACE. For energy purposes, space within
a building that is provided with heating and/or cooling equipment or
systems capable of maintaining, through design or heat
loss/gain, 50°F (IO°C) during the heating season and 85°F
(29°C) during the cooling season, or communicates directly
with a conditioned space. For mechanical purposes, an area,
room or space being heated or cooled by any equipment or
appliance.
CONDITIONED AREA. That area within a building provided
with heating and/or cooling systems or appliances capable
of maintaining, through design or heat loss/gain, 68°F
(20°C) during the heating season and/or 80°F (27°C) during
the cooling season, or has a fixed opening directly adjacent to a
conditioned area.