Hello-
I am curious to know if anyone is aware of research or other work that
has investigated the impact of including the mass of the wood or
steel-framed cavity/insulation layer in the opaque surface definitions
of whole building energy models.

I am aware of ASHRAE RP-1145, which outlines a method for developing
"equivalent wall" models of various assemblies, and appears to include
the mass of the framing/insulation layer. However, this research does
not appear to evaluate the impact of mass of this one material layer
separately. I believe it is common to account for mass of other layers,
particularly concrete/masonry, but my experience is the cavity layer is
only simulated with thermal resistance and no mass.

Any leads would be appreciated.
Thanks,
David