Hello Guest - ideas on 'Close to house/drains' can vary? So could you be more specific? If left unpruned Cobs can reach to around 20 feet. As a general rule of thumb most tree roots are the same spread as the branches. Cobs are often pruned to about 7ft and grown in groups or hedges. I had a cob in my previous house which I never pruned it had multi stems rather than a single stem it never got that big about 8 -10ft high and about 5-8ft wide it was about 20 feet from my house/drains.

Guest, you say it is a twisted cob, a Corylus Contorta. I understand that they only grow to about 10' tall and are grafted onto a rootstock of the ordinary Corylus. I have one, which sometimes developes a straight shoot which has come from below the graft and needs to be removed. Also as far as the spread is concerned, I just prune to maintain the shape I require.