How to Solidify an object without ruining the geometry?

I’m making a building and I’ve modeled it exactly to the measurements of the real one it’s based off of, but it’s my first time doing a an actual interior scene, and I didn’t realize until after I finished about half that I needed to solidify it for the lighting to work properly. When I try to Solidify it now, it makes the mesh bigger, so the measurements don’t match anymore.
Is there any way to make it Solidify only the space inside the walls, so the visible part of the mesh stays the same?

Set the offset to -1 and use a positive thickness

Thanks! That worked!