Question
I am almost ready to start excavation for the foundation of a house in East Texas.  One end of the house will be lowered about 3' into the existing slope. There is a large (20"-24") Red Oak or maybe a Water Oak on that end of the house.  I'm planning on building a retaining wall 3' high between the house and the tree.  My question is, how far do we have to stay away from the tree with the wall to be sure we don't kill it?  We are limited on how far we can move the house.  Thanks much for any advice.
           Bil

Answer
The roots of a tree will extend about 1 1/2 times the width of the branches. A tree can survive root cutting if the amount of roots cut does not exceed 25-30% of the root system. This includes adding soil over the root area or taking soil away from the root area. The root system can be measure roughly by drawing a circle around the tree where the ends of the branches hang and then estimate the area to be cut or filled and calculate the percent damage. The roots will extend further than the branches but these will be smaller and can with stand cutting. The other thing IF you do this MAKE SURE you rope off the rest of the tree and the roots zone so NO traffic of machinery goes in this zone --this will protect what is left of the root system from compaction etc. The heat and lack of moisture in the summer months will also effect the roots left. You may want to call the Texas Forestry Service (a state agency) and ask one of their Foresters to take a look they may see things on the ground that can not be described in  question. Their phone number should be in your local phone book.