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I'm going to be building a deck next week in my backyard! I'm very excited for the project, but I'm concerned about one thing: digging the foundation holes. I have an inground sprinkler system, and I'm concerned that I'm going to hit a buried hose when I'm digging.

How am I supposed to find where the hoses are? Also, what if I start digging and find a hose.. Can I move the hose, or do I have to move the hole?

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I spent a couple summers in college installing underground sprinkling, so I know a little bit about this.

Typically you will have a large valve box somewhere in your yard. These will usually have an access hatch (or several small hatches) for maintenance, so they should be easy enough to find. Typically a pipe will run from the water supply to the valve box. From the valve box pipes will run out to the various sprinkler heads.

Each valve in the valve box represents a single zone. When the sprinklers come on, a valve will open and all the sprinklers in that zone will come on at the same time. You can tell (roughly) where the pipes will be for that zone by finding the shortest path from the valve box that connects all the sprinklers in a zone.

As long as you dig carefully, you shouldn't have too much trouble. The pipes are usually pretty tough and are usually buried about a foot or so under the ground. If you do run into one, you're not going to be able to move it without doing some serious trenching, so you'll most likely be stuck moving your hole instead.

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  • Irrigation systems usually use a 200 PSI PVC pipe, which has a thinner wall than the Schedule 40 PVC pipe used in home DWV systems. 200 PSI PVC pipe might survive one strike from a shovel, but they can be cut fairly easily by a determined thrust of the shovel. So, they’re not fairly tough. And blow torches aren’t used for PVC pipe, as another answer states. If you find one in the path of a footing, you will need to enlarge the hole and route the pipe around the footing. You’ll need extra pipe of the same size, 4 elbows, PVC primer, PVC cement & a PVC pipe cutters. – jaschwa Mar 20 at 8:31
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I am not sure if there are tools out there for detecting the water in the pipes but I would think they are pretty expensive.

For the most part though the lines will run from one sprinkler head to the next in a straight line (or a gentle curve). If you run into an irrigation line you can most definitely move it. Just use an extra piece of pipe and a coupling on either end (plus two hose clamps). Lowes or Home Depot will have the right sized coupling and hose clamps for your line diameter. I have broken my sprinkler line twice in my garden (the line runs directly underneath) and patched it both times like this.

Be careful not to pull too hard on the line or you could end up pulling the entire line under the ground and move the attached sprinkler heads. In other words don't just try and stretch the line around your hole and put pressure on the entire line... eventually it would move the head.

EDIT: Eric Petroelje is right that you would need to do some serious digging to give yourself enough room to work and get the pipe around your footing hole. But if the footing hole location cannot be moved then it might be necessary.

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    If you do end up having to patch a line, a propane torch can come in really handy as well. Use it to heat up the end of the pipe slightly and the fittings will slide right in nice and easy. – Eric Petroelje Aug 5 '10 at 13:33
  • I forgot about that trick to slide the fittings together! Or just use one of those hand held grill lighters. – Jeff Widmer Aug 5 '10 at 13:57

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