Question
We are constructing a building in Southern Maryland and have been instructed to install 6 Northern Red Oaks along the street edge.  They are to be planted 6 feet off the curb.  The street centerline is 12 feet off the curb.  There is an 8" terra cotta sewer main 6' beneath the street, about 12' off the curb.  The trees will be about 18' from the terra cotta pipe.
How wide and deep do Northern Red Oak roots grow?
How long before these roots become an issue for this sewer?
Thanks in advance for your response.

Answer
The vast majority of roots of oak are in the first three feet of soil. Oak does not have a tap roots and a sewer pipe 6 feet down will have no effect from the roots. With the pipes under the street the roots will not be a problem since the roots will not grow that direction since there will be no water under the street. The roots will grow away from the street and could damage walkways if these are present BUT this will be many many years down the road. The main problem that could arise is the branch hanging over the street. The height of a mature N. red oak is 50-60 feet and the spread is about the same. The lower limbs will need to be pruned as they reach the street to keep the branches from hitting cars.
The roots are not an issue.