When the selection is empty, you can't get closer than the limits of the bounding box of your home. But you probably activated the Aerial view centered on selection option in Sweet Home 3D preferences panel and selected an object in your home, in which case you can get closer.
You can reproduce the same behavior in Sweet Home 3D JS, by setting the same option and selecting an object by program. Just call setAerialViewCenteredOnSelectionEnabled and setSelectedItems. See also omrico request here.