I'm new here and hoping someone can guide me a little bit. Our 20X40 in ground pool started yesterday. At this point we are completely dug and all the walls are up. The installer (who has already tacked on an additional $750 for travel fees) has told us that we should put a concrete base down underneath the vermiculite to prevent settling and tree roots coming through and puncturing the liner down the road. The house was built 6 years ago on a wooded lot, so there were lots of tree cut and roots left behind. The other reason he gave was the ground was softer (probably due to the back filling for the house 6 yrs ago) and stated that even if we cut the roots off, the ground will settle and they can push through. We are looking at anywhere from an additional $1000-$1600 for this. Is it necessary? I hope someone can guide us on this!! We are really torn on what to do. He is due to come back Friday and start back up again.