What is the minimum depth a water line must be in zone 6 and pure medium to course sand?
user_6992381
| Posted in General Questions on
I know there must be code requirements but there must also be some scientific way to know at what minimum depths a well water line will not freeze, because I’m thinking the soil composition would be a significant factor. I am in zone 6 in Traverse City, Michigan in pure medium to course sand and on a hill 35 feet above a small lake. The sand is very dry.
Also, can I use Pex underground from the well to the house? I have heard that it is somewhat flexible and resistant to cracking or bursting if the water freezes.
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Hi, first, can you tell us your name? The software is buggy and is not currently showing the name you put in your profile.
The IRC building code requires water lines to be 6" below the frost line for your location, unless "adequate provision is made to prevent freezing..." A rule of thumb is that every inch of foam you put over the water line allows you to raise the water line a foot. The closer you get to the surface, the wider the foam needs to be. More information here, at P2603: https://codes.iccsafe.org/public/document/IRC2015/chapter-26-general-plumbing-requirements.
Water lines from wells are usually plain polyethylene, which is fairly rigid. PEX (cross-linked polyethylene) is more flexible, and can be buried, but is often run in a conduit to prevent puncture damage, and also makes potential replacement a lot easier. Local conditions and norms vary a lot in this regard.
Frost depth will vary a lot within a zone. You should be able to get a frost map for your area. I don't know how much soil composition affects frost depth, but the map should account for it anyway. You can certainly use PEX, but honestly using PEX for the purpose of freeze protection is bad planning. It's less likely to burst than standard poly, but not immune. It makes more sense to just go below the frost line, which is preferable to using insulation. I personally don't trust the 1" for 1 foot rule of thumb, it doesn't make much sense to me. The pipe is surrounded by soil which is presumably prone to frost, how is insulating just one side of the pipe going to help? Would you insulate a single wall and expect to be warm standing on one side of it? Just picture 3 feet of frozen ground, now imagine a 1" thick, 6" wide strip of insulation inserted at a depth of 2 feet in that frozen ground. What exactly is warming the 1 foot below it that supposedly is going to make it not frozen? Not the water pipe. Not the hundreds of tons of earth around it that is also frozen. It may make sense if you are guaranteed to have a continuous stream of water, as in a public main, but for an individual residence that is going to have stagnant water a significant portion of the time, no.
Thank you very much for your answers.
I have unique circumstances which require that I have a better understanding of all options.
Sorry, I forgot to include my name in my first post. Tony
Trevor, have you heard of frost protected shallow foundations? Similar concept. The ground only freezes because the air above is cold. The earth below is warm. By placing insulation above the pipes, you prevent cold air from reaching the pipe (via frozen ground). I have thawed frozen ground in January, in Maine, by placing a sheet of rigid foam over it for a week. (I was late planting tulip bulbs one year.) The ground wants to be warm; it just needs to be protected against air from above. That's why the width of the foam is also important, and needs to be wider as you get closer to grade.
That said, the 1" per foot is just a rule of thumb, and should be used cautiously. Plus it's a waste of foam, if your ground allows you to dig below the frost line. I live in an area with very shallow bedrock and it's not always possible.
Scale is important. The foundation covers a huge area compared to insulation over a pipe. I just don't see a narrow strip of foam as much of a barrier when surrounded by highly conductive soil. If I had no other choice, I would be making that insulation about 2 feet wide. I would also suggest that the insulation requirement would go up exponentially as the burial depth decreased, since it's also moving further away from the heat source.
Trevor, I don't think anyone is proposing that a narrow strip of foam works. I don't know of any specific guidance on the width needed, but the frost protected shallow foundation guidelines probably could be extrapolated to get an idea of what is needed. I think 2' would be a minimum.
2' to 4' wide foam is what I usually see used. I've done this a few times, and the excavators I have worked with do it regularly. The rule of thumb I mentioned is to increase the insulation thickness as you get closer to grade.
In my area, zone 6/Maine, unheated buildings with frost-protected foundations, with foam 14" below grade, for frost protection the foam needs to be R-10 and extend 49" beyond the foundation. So if your water line is 14" from the surface, you would want the same, or thicker foam that doesn't project as far. As you go down, the width can be less, until you don't need any 6" below the frost line. (Frost actually penetrates lower than the official frost line; it just doesn't usually cause damage that far down.)
If foam needs to be 8' wide a foot below grade and 0' wide down 4', if we assume a linear curve, that indicates 64" wide at 2' below grade and 32" at 3' below grade. With thicker foam it wouldn't need to extend as far, and the curve probably isn't linear, but it gives an idea of what to expect.
A useful guide;
http://msdssearch.dow.com/PublishedLiteratureDOWCOM/dh_0031/0901b803800311e8.pdf
Malcolm, that's a very useful guide! I don't believe I've seen it before, thank you. I just ran through their calculations. For my area they call for R-10 foam, and in the horizontal assembly we're discussing, it would need to be 44" wide at 2' below grade and 18" at 3' below grade. More forgiving than my guestimates in post 7.
Help me calculate this. In a flat installation, not inverted U. Using 4 inches of blue board. Frost line 5 feet. The waterline is 24 inches down. How wide would I have to go. A different question, If you made a 4 foot wide soil berm 24 inches high, is that equal to 24 inches of ground to level grade. I was wondering if you had extra soil on site if that is another option. Thanks for any advice.
You’re much better off just burying the line at the proper depth than you are counting on foam board to perform magic. I would not trust foam board here, especially over any significant period of time.
Bill
My problem is I cannot get down below the frost line and need to figure out some ways to prevent the line from freezing. I heard a lot about how blueboard working so well. I was hoping some berm and insulation where it is most shallow. Thanks.
Our house in Colorado sits on a ledge of rock and has had problems since before we bought it about 3 years ago. I have found this company in Canada called Heat-line and it seems amazing to me . They guarantee no more freezing . I am wondering if anyone has ever heard of them or used them. I love the product but partners are sceptical. Yet pipes can be laid on the ground, insulated of course. I would love to hear what people have to say. Make sure to find the right Heat-line.
That's likely just electrically heated cable. Will work great until you have an extended power outage. Probably a good idea to have an automatically switched back-up generator.
Yes, everyone has outages . This allows you to live year round in your dwelling whether your water pipe is lying on top of the ground or 6’ under the ground . No need to blast. You should really look at it