Question
I plan to excavate a steep hillside for a boat house foundation between a pair of large oak trees (32" diameter).  The trees are approximately 32 feet apart.  The trees are approximately 25 feet back from the ordinary high water mark & about 10 - 15 feet above the water line.  The location is western wisconsin.  Soil is sand w/ some rocks (glacial morain)

If i center the boathouse between the trees, there will be about 6 feet between the trunk & the foundation wall.  Would it make sense to move the foundation closer to 1 of the trees in order to minimize the damage to at least one tree?


Answer
I think it would be better to try and center the house between the trees. You will be dugging a large amount of roots but if you stay 6 feet or more from the trees the root systems should be ok. You may see some of the limbs on the cut side die from the root cutting. After this is done I would recommend that the trees be fertilized to help the roots left to compensate for the damaged roots.
Here is a web link that will give you informationon how to fertilize a tree and the amount to use, http://www.ces.ncsu.edu/depts/hort/hil/hil-618.html