I have a customer who wants a row of trees installed to create a barrier between her house and a house located behind her. The area is heavily wooded but the existing tree canopies are fairly high, I would say thirty to forty feet. The property is a large area so space is not a real issue. However this area does stay shaded other than a little broken sunlight and of course throughout winter. What would be a good choice of tree or possibly even a shrub that would work and of course it needs to provide screening year round. I am thinking that I need to at least get about fifteen to twenty feet of height for them to serve the purpose. We are in zone seven and this area is a transition from the foothills to the Blue Ridge mountains. Thanks for any help.