Historic Building Question in Sacramento; Building Permit

[Nicholas Lohr]

I am trying to build a free standing duplex in the back unused part of a parcel that has an old historical landmark building towards the front it. 

Attached and already existing to the historical building is an addition that was built later than the original historical part.

In Sacramento there is an ordinance that says any new building must be 40 feet away from the historical landmark.  This ordinance is the last hurdle I have to get past in order to be approved to build.

If we have to measure the 40 feet from the edge of the addition to the historical part of the building then there is no project.  If we get approved to measure from the ORIGINAL historical structure then there is more than enough room.

Can I argue that the 40 foot measurement should be taken from the original building rather then the edge of the whole structure which would include the addition?  Does anyone have any experience with this?