Question
Want to build a deck in front of house, but have huge old Oak tree right in the middle of the house.  How far away would the supports have to be in order not to kill this beautiful old tree?

Answer
You would need to carefully hand dig the support holes and find locations where you don't hit and roots bigger than your arm.
Some times that can be right next to the tree,  some times further away. Depends on the tree. Or you could use those concrete pedestals and not put anything into the ground in this area at all. This option is good if there will be lots of other locations to attach to the house our footings below grade.