I added on 8 zones to a condo complex yesterday off of an existing system. All of the valves were 18" deep and buried. We had to dig 5 huge pits. They also used red field wire. (1.5" Weathermatic valves with clocks every few units and they used field wire.) What's up with that? It's only about 3 years old, the system. The only good thing was that all of the pipe was about that deep, too. I had to run lots of new wire and would've torn up most systems doing that. It was a bid job so I was scared we'd spend a few hours patching it up and running through it. Only hit one line.