I have very limited experience with them myself but I had one neighbor who installed his own system using PVC about 4" deep (he'd had no previous experience and didn't do enough investigation first). We don't get a lot of cold weather in the Dallas area, but ever once in awhile (23 degrees this morning), and he also did not install the self draining valves (I'm not sure of the proper terminology). So . . ., we had a good freeze and his entire system shattered. Then I helped another friend install his system, but he had a professional design it; 8 zones, 12 heads per zone, drain at the end of each run, rented a ditch witch and put everything 12" deep. It, too, was schedule 40 PVC and I asked a couple of the guys helping if they weren't being far too generous and careless with the cement (or solvent). They were sure that you couldn't use too much. Well, that ain't so. I later helped him dig up and fix two leaks. In both cases, the solvent had pooled in the line and simply ate a tiny hole right through it.