if you replace older Foundations with stronger new ones.
By upgrading my House i had really problems to see, if the new foundation will replace the old one, also the same replacing walls and detect if i place the new wall right (inner and outside).
Kinde sad, lot of mats wasted cause of this. Also would be awesome if we are able to replace also lower leveled foundations with never one. Guess currently its only possible to replace existing foundations on the top.
(sorry very bad english)