I have very large ficus growing near a corner of a building. It is very overgrown. My gardener has suggested trimming the tree significantly and says that will significantly reduce the expansion of the root system, thereby protecting the building from further root growth. Is he correct?
The best thing you can do is water your tree. It will not have to go searching for water. You should also dig a trench about 2 feet deep and cover your foundation on the side with your tree with galvanized metal, making sure you have air between the foundation and the metal.
Trimming the tree is fine for health but not for reducing root systems. How silly. In fact, too much pruning of the top growth will enhance root growth just because there is a large amount of energy the plant needs to put somewhere...why waste all that work making food if it can't be stored in the roots?