I think one of the big issues that face all the 3D house printing companies I have seen is how once you put a nail in a wall to hang a photo there isnt a great way to really fix it. Since concrete makes up inner and outter walls its just something that I feel like you are pretty set with. Additions seem like something that would be extremely difficult and say a pipe broke in a wall and a huge section has to be cut out... just yikes.