It's going to vary from state to state. In my state they added this to the Residential Code:
1.1.7.3.1 Detached one- and two-family dwellings.
Detached one- and two-family dwellings, lodging
houses, live/work units, townhouses not more than
three stories above grade plane in height with a separate
means of egress, and their accessory structures
may be designed and constructed in accordance with
this code or the California Building Code, but not
both, unless the proposed structure(s) or element(s)
exceed the design limitations established in this code,
and the code user is specifically directed by this code
to use the California Building Code.
And this to the Building Code:
1.1. 7.3.1 Detached one- and two-family dwellings.
Detached one- and two-family dwellings, lodging
houses, live/work units, townhouses not more than three
stories above grade plane in height with a separate
means of egress, and their accessory structures, may be
designed and constructed in accordance with this code
or the California Residential Code, but not both, unless
the proposed structure(s) or element(s) exceed the
design limitations established in the California Residential
Code, and the code user is specifically directed by
the California Residential Code to use this code.
Basically, you can't cherry-pick. It's either Building or Residential, the one exception is that the Residential Code does refer the user to the Building Code for a select few items. Then, and only then, a Res code design can use certain parts of the BC. But that's in CA, not sure what you have.
