Family Handyman DIY Tip of the Day: Inexpensive Wet Basement Solution. Sloping the soil away from the house will take care of the problem most of the time. Firmly pack clay soil around the foundation, with at least a slope over the first 4 ft.
Don’t use too many fasteners. This gives the tree room to move and grow. Even for smaller, lighter tree houses where the load is spread over three or four attachment points, consider using or lag bolts.