Within the treatment, Rehabilitation, an attached exterior addition to a historic building
expands its "outer limits" to create a new profile.
Because such expansion has the capability to radically
change the historic appearance, an exterior addition
should be considered only after it has been determined
that the new use cannot be successfully met by
altering non-character-defining interior spaces.
If the new use cannot be met in this way, then
an attached exterior addition is usually an acceptable
alternative. New additions should be designed
and constructed so that the character-defining
features of the historic building are not radically
changed, obscured, damaged, or destroyed in the
process of rehabilitation. New design should always
be clearly differentiated so that the addition
does not appear to be part of the historic resource.