conifers near house

A question about : conifers near house

I have I think Port-Orford-cedar conifers as close as 8 feet to the front of my house, they look about 15 feet tall. does anyone know at what height I should cut them so it stops the root going to deep, and how deep the roots can be related to the height of the tree?

and does anyone have any online resources showing how far back into the branch they can be trimmed? I keep hearing that they shouldnt be trimmed back into dead wood but does that mean i need to leave a layer of green leaves? the green leaves dont go back that far, its all dead looking brown leaves. I wont be doing it myself, I just ant to know the guy i get to do it can verify it to me.

Best answers:

• AKA Lawson cypress?
• I have a professional company cut my conifers every December,they do a great job and trim the height to six metres and trim the foliage back,but not to much.
  They look great when cut,so neat.it takes four days i have sixty around the perimeter of my garden
• Don't forget that conifers do not regro from old (brown) wood so if you do cut right bac they will have to grow from elsewhere to cover up the dead stumps.