It should easier to add a pipe to the existing valve box. For example my valve box can accomodate upto 6 zones, only 5 there now. Also, you could tap into the water supply and add a new valve box. I think either method would work. Finding existing pipe is another story.

I'd like to add zones to my system too. I have a RainBird controller that can go as high as 12 zones. I currently have 7. I want to add 2 more, perhaps 3. But I'm perplexed. I have two boxes in the yard. One has 4 valves, and the other has 2. The guy who installed it told me the box with the two valves was for future expansion. Though, if this is the case, how can the 4 valves in the other box control 7 zones?

Timmboj:
You need to confirm that you truly have 7 zones:

Open the controller panel and find the control wires. For 7 zones, you'll have 8 wires connected including the common (usually white, sometimes green, ALWAYS connected to "COM" terminal).

Which Rainbird clock is it? Repost here and we'll take the next step...

Thanks. It IS just six zones so far. Thought I had seven. I can't find my book (I swear I saw it just this past weekend). I was just out looking at the unit, and it can go up to twelve zones, but I didnt see any model number. Anyway, so apparently those two valves below the driveway control those two zones. So how do I expand from there? I'll locate my book tomorrow and get you the part number.