SPRINKLER TALK FORUM - You Got Questions, We've Got Answers

One foot is deep enough. This is especially true when poly pipe is being pulled over deeper underground utilities, which can be (by code) as shallow as 18 inches.

Thank all for your comments.

I think I'll go 18-24 inches; we'll see how the trenching goes tomorrow. I'll try to post pictures.

The ground is hard as nails. I just dug one of the valve box holes and it took me an hour!

Thanks again team!

It wont fail if you are 8 or more inches under the ground. Pvc will be fine too but just be sure to blow out the system for the winter. I do agree if you think youll dive over an area it should be deeper. the reason i like poly over pvc fro the majority of a system is if for some reason it were to move...heaving of the ground driving over it etc poly is more flexible and will move but pvc can crack. dont get me wrong many systems are 100 percent pvc and are fine.

wiredup,

The Water Authority recommends 2 INCHES? (Did you mean feet).

Well here's my input on depth based on my research before I installed my irrigation system.

1. I believe that plumbing codes typically require any mainline pipe (pipe leading to the control valves) not made of metal to be buried to a depth of 18" (as measured from the top of the pipe to the soil level).
2. Deeper is safer (more protected from freezes and potential vehicle traffic).
3. 10" to 12" were the most common suggested depths for latteral lines in irrigation books and www.irrigationtutorials.com (here's his page on pipe instilation: http://www.irrigationtutorials.com/instal14.htm )

I could definitely see where shallow installations fail within 2 years not so much from freezes but because people forget the underground pipes, and then run over them with a vehicle. A simple example I can think of is you purchase 12 bags of mulch for that landscaped area and you load them up in your SUV. When you get home, you realize that if you park at the curb, you are going to have to make 12 trips to haul those bags from the SUV to the landscape area. You decide that it would be a lot easier to just drive through the lawn, drop the 12 bags on the ground, and drive back to the curb. You forget about those pipes, and a shallow install results in broken pipe.

I've never hear of freezing temperatures affecting PVC, assuming there isn't ANY water in it. 32 degrees is just a magic number for water, not PVC.

Thanks Pete--the only thing I'd say is the Leesburg Water Authority said recommended the depth at 2". He said some of the irrigation system don't put them in deep enough and the systems fail within two years.

Do you attribute that to a failure to winterize the system? I guess the next question I'd have is: does PVC fail when it freezes despite being clear of water?

I wouldnt suggest going that deep due to mainenance. If you ar that deep it will be harded to work on in the future. Just go 8 inches and make sure you blow out the system before winter.

I would suggest using 100 psi poly for your situation. but it is up to you.

Thanks folks--I do happen to be in place where it freezes (Northern Virginia), however I intend to install everything well below the freeze line (12")--I'll go 24".

the black pipe is called poly pipe and it works very well in climate that freeze but it is not recommended for the main line ie before the valse due to the constant pressure unless you use 160 psi poly. I use 90percent poly.

PVC in sunlight can have a shorter lifespan, but underground, it doesn't seem to suffer.

I laugh when I see plumbers working on sprinkler systems. Most of them are clueless. I can't tell you how many times I've had to redo their work. Many many. I vote for white schedule 40 PVC. Let me add I'm in So. Cal where it doesn't freeze. I'd say 99% of all new installation here use white pvc. I did see an all copper system once. Unbelievable! Lateral lines included. Good luck!