Question
What type of root system do they have?

Answer
Not real sure what you are asking--they have a more fibrous root system which will not harm driveway, walks and house foundations. As most trees if there is a break in sewer pipes the roots will get in the pipes. This could be a problem only in the older clay type sewer lines not the newer plastic pipes. They generally cause no problem with roots. The roots a more spread and extent about 1 1/2 times the width of the foliage and do not have much of  a tap root.  I hope this is what you wanted if not, please ask again.