Finishing the details for my out building. I want to run a water line out to the building and most people around here will say 6’ underground which will be one heck of a trench in the sand that I have.

Do you think the depth could be less if it is sprayed with spray foam when i have the boiler lines sprayed?

It would be a lot easier if I could stay at 4’ or so.

gg

Frost line varies tremendously with soil, water table, vegetation, snow cover etc. 

I’ve cheated at 4-5’ and gotten away with it, and many, many lines freeze at 6-8’.  I had one that didn’t melt until the middle of spring one time! 

If you cheat, I’d cover the line with a piece of foam as wide as the trench before you backfill, you want the heat to come up from below and not be lost to the surface, unless you’re going to be using the line consistently, then it may make sense to insulate all around it.

Unless this is running in the same trench as the boiler lines?  then just put the cold water at the bottom and the hot water right in the middle!

goosegunner - 01 September 2010 08:44 PM

Finishing the details for my out building. I want to run a water line out to the building and most people around here will say 6’ underground which will be one heck of a trench in the sand that I have.

Do you think the depth could be less if it is sprayed with spray foam when i have the boiler lines sprayed?

It would be a lot easier if I could stay at 4’ or so.

gg

For 99 out of a 100 winters 4’ would be certainly be plenty.

If it’s going in the same trench as the boiler lines you could just place the line in the bottom below the other two, which would probably give you the little extra you need.  If you’re real concerned you could place a 2’ X 1” sheet of blue styrofoam on top of the whole mess, which would have the effect of lengthening the path that the cold would have to penetrate.

Personally have been getting away with running a water line 8” below the surface under a 4’ wide sheet of 1” styrofoam, and have made it through a few very cold months with no snow cover through the years, but even so I’m not willing to bet it will never freeze.  Our building code frostline standard here is 48”.

—ewd

benjamin - 01 September 2010 09:11 PM

Unless this is running in the same trench as the boiler lines?  then just put the cold water at the bottom and the hot water right in the middle!

Don’t really understand what you mean?

Yes the water line will be in the same trench as the boiler lines. The guy that drilled my well when we built said it is always a good idea to run water lines in a drain tile in case you ever have to pull a new one.

It would be cheap insurance.

gg

I’ve got my water line to the yard hydrant buried 4 to 5 ft below grade. The area it runs through is flat, which may make a difference. Its about a 50 ft run. I’ve never had it freeze, this will be the 8th winter in service I use it every other day or so to water the animals in the winter. I’m in Green county - about as far south as you can go without being in IL. If you’re farther north you may want a bit more depth.

I worked with a water utility years ago that did a study on burying waterlines and frost depth. There was a major difference in frost depth in soil that is covered with snow or uncovered (like a driveway or walkway). The frost depth under the road could be 2 feet deeper.

The local utility in the adjacent town (Berlin NH), has a lot of experience with shallow water lines as the majority of the city is on rock. If at all possible they go down 6 feet, but in areas where it is not practical, they lay 2’ wide foam board on top of the water line in shallow areas. This keeps the cold from getting to the water line and allows the heat in the ground to keep it above freezing. The claim is that it is more effective than actually insulating the line, althouhg with a boiler you will still want to insulate the line rather than heating up the ground.

goosegunner - 01 September 2010 09:43 PM

benjamin - 01 September 2010 09:11 PM

Unless this is running in the same trench as the boiler lines?  then just put the cold water at the bottom and the hot water right in the middle!

Don’t really understand what you mean?

Yes the water line will be in the same trench as the boiler lines. The guy that drilled my well when we built said it is always a good idea to run water lines in a drain tile in case you ever have to pull a new one.

It would be cheap insurance.

gg

Mostly I was joking about the hot water line, but if there were a reason to have hot water it would work, it may be useful at some time to have an extra run of pex for whatever reason, and 1/2” pex is pretty cheap. 

If they’re all in the same trench, you’re obviously not going to have to worry about freezing when the boiler is running.  I’d put the water supply on the bottom of the trench, add the layers of foam and spray your boiler lines on top of that, then the water line isn’t inside the foam so you get some idea of the heat loss off of the insulation, and the sheet foam saves a bit of the spray foam.

Depends on how you are going to use the line.  If it’s a main loop that will be constant circ there’s really no reason to make it that deep. Sure you could run into an “end of the world as we know it” situation with sub zero temps and no electricity for a couple weeks but I think you can figure the odds of that happening.

I have seen water lines here freeze solid around here that are 6-7’ down when they are under driveways and there is no flow.  Most people I see go 3-4 for boiler lines. We do nearly all of them at 3’ or less due to ground water issues in a lot of areas. That can be a much worse problem to deal with. Some are as little as 2’ down and if you insulate right it’s no problem. The heat loss doesn’t really change that much considering you are running through dirt that maybe only 10-20* different in temp from 2’ down to 6’ in depth. 

The keys to never having a problem are good insulation and constant circ.

Now if you want to set it up so you can shut the heat down for a month in mid winter the only 100% safe thing to do is antifreeze the loop. That’s why I always try to set up my systems in a way that enables me to pressurize and seal the outdoor section(s) via the use of a HX if required.

Whoops…...........just re-read your post and you are talking about a fresh water line right?

If so…. 4 feet down with 2” of foam over the top or 6’ down if it’s under a traffic area.

The domestic water line will be rarely used. It will likely go weeks or months with no flow, but I think it is a necessity to have water in the shed.

gg

I don’t know where you are at in Wisconsin. But I’ve always went by if your in southern Wisconsin 4 plus feet is good. In the northern part of the state 6 feet is normal.

I live by Green Bay and would go 6’ instead of 4’.  There are years when we get the cold weather without much snow cover.  I personally have had to deal with frozen lines buried 6’ under a driveway that was bare (no snow pack).  It was not fun having to drag out a garden hose every day to be able to water the animals. 

It doesn’t take that much extra time to dig the extra 2 feet.  You will have to watch for wall collapse more when you are in the trench, especially if the soil is very wet or not well packed.  Some sands will keep caving in while you are digging, making for a very wide trench to get to the desired depth.