Low mortgage interest rates have pushed home builder sentiment to an index high of 71 in October, up from 58 in September and the highest level in 20 months, according to the National Association of Home Builders. Any reading over 50 indicates that confidence is improving. The dramatic increase in sentiment is due to the plunge in rates over the past year to roughly 3.5% from 5%. That drop has led to much greater demand for new homes.