Any help regarding the reuse of an existing building LEED simulation would be helpful. We are working on an existing building that was a warehouse and is now an office building. The existing shell was un-insulated concrete block walls and an un-insulated metal roof with metal joists. Using the ASHRAE 90.1 guidelines for envelope allows the use of existing envelope, but in the climate zone at-hand our proposed envelope alone represents a 30% energy cost savings. Our question is whether there is an exception or limitation to using existing the envelope if a building use is changed, ours is now an office.

Thanks,

Ken