Normally Occupant Area is measured to CL of tenant demising walls. However I've run across a situation where the demising walls are up to 24" thick, and mostly solid masonry. To add to the complexity, there are chimneys and chases buried in the thickness of the walls in places that cannot always be determined. Furthermore, some tenants own both sides of such a wall.

Should tenant USF should exclude the walls b/c they are permanent building elements surrounding Major Vertical Penetrations? How about if such a wall is in the middle of a tenant space? Given relatlively narrow tenant spaces, this calculation significantly affects USF and RSF.

Is there any precedent for dealing with this situation?

Thanks!