Boolean difference failed - terrain with volume

boolean difference failed.3dm (325.6 KB)

in same cases it worksbut i cant figure out whats its wrong…can someone help??

booleans operations needs a closed intersection between objects. if you close your building using the Cap command and maybe moving it a bit down. it works
the Dots marks where the intersection is open or not clear enough:

thnx a lot…!!ok for cap …move a little bit u mean for e.g. 1mm, 5cm??cause its my base for the building…i dont want to lose the regulation with the terrain…

I’m not at my Rhino computer right now, so can’t open your file. However just looking at your screenshot I assume you have a single surface as the terrain and a poly surface as the building outline. If this is the case it is only necessary that you make sure the building outline is completely joined at all the corners and that it intersects the terrain all the way around it’s perimeter. With these conditions met you should be able to trim the terrain with the building outline. Click the terrain inside the building to delete it when running trim. Or you could run intersect and then delete the part you don’t want afterward.