Question
I was putting in a french about five feet from a grove of redwoods. Two
readwoods growing out of the same trunk are both about 30 years old. a bout
75 feet or higher. Diameter is about two and half feet. The person who was
digging the trenc cut through two very large roots that were off of one of
trees. The diameter of one root was aboutsix inches the other about five
inches. The area around the redwoods is damp and shady as it is in a grove of
several much larger and older redwoods. the cut is clean. I'm angry that I  
allowed him to cut the roots. David

Answer
A tree that size will have a good root system and the soil is wet enough to allow the remaining roots to compensate for the lost of the cut roots. The fact that the cuts were clean will keep disease from entering the root system. Think of the area of the root system as a pie and when you slice across the pie shape you can calculate the amount of area that was cut off. In a root system this should be not more than 20% of the total area. The closer you cut to the trunk the larger the % will be , so if you cut away from the trunk there is usually no problem. In this case it is done so all you can do is wait and see. Usually the worst that happens is the tree will loose some of its foliage on the side toward the cut roots. Over time a tree this large will recover and have no long term effect on the overall health.