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Small Cabin Forum / Cabin Construction / Underground water line insulation
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Dom08
Member
# Posted: 13 Sep 2021 01:52
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Hello,
I am looking for some guidance for insulating water lines.
I am hand digging a trench to pull water for our cabin from the lake. The property is extremely steep so no machinery is able to help digging. My plan is as follows:
Hand dig a trench 180ft down the property slope to the lake. Height from lake to the building is 90ft.
Trench is going to be about 12-14 inches wide by about 1-2ft deep.
I am looking to insulate the lines to prevent freezing during winter.
I will place a 3inch conduit in the trench. I will be boxing rigid insulation around the conduit (bottom, sides and top) i will fish my 1inch water line inside of the 3" conduit.

Does anyone have any idea on calculating r-value for insulation to prevent freezing?
Winter months we hit -15 to -20 dry weather.

Irrigation Guy
Member
# Posted: 13 Sep 2021 07:10 - Edited by: Irrigation Guy
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How deep are you trenching? If you have the pitch a drain back system might be better.

If you are insulating I have read it’s better not to insulate the bottom. Heat from the ground rises.

ICC
Member
# Posted: 13 Sep 2021 09:12 - Edited by: ICC
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Insulating a buried water line will not prevent it freezing. Insulation only slows the movement of heat. It does not stop the movement of heat. Heat always moves from the warmer place to the colder place, until both places are the same temperature.

Depth is what prevents water pipes from freezing. Every location has a rated frost depth. The further north the deeper it is. Bury deeper than that and it will not freeze.

Water that is moving through a buried pipe will not freeze. People here in old homes leave a tap running slowly when we get unusual cold snaps to keep the water pipe from freezing.

Dom08
Member
# Posted: 13 Sep 2021 11:47
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Thanks for the information.

The incline is so steep that i have to make steps for my trenching that i have started. Our frost depth is rated 6 ft!
I have read that there is an old rule that every inch of rigid insulation placed accounts for 1ft of depth....
Since i can't physically dig 6ft depth at 180ft long with a steepness that i can barely stand on, i figured i can dig 2ft down and load it with rigid insulation. If possible 6inch of rigid insulation.

Nobadays
Member
# Posted: 13 Sep 2021 12:10
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As Irrigation Guy said.... your best bet is a drain back system. I'm sure there are other ways but a submersible pump in the lake pumping into a holding tank at the cabin, (possibly a bladder or pvc tank under the cabin if it doesn'tfreezeunderthere)... no check valve, so once the tank is full the water in the pipe can drain back through the pump into the lake. A Shurflo pump could pressurize the water for cabin use. In the winter you could have an interior tank if freezingunder the cabin 8s an issue.... we use a 50 gallon for drinking water and a 55 gallon barrel plumbed to the toilet tank (both in the loft) for winter water if we have to drain the whole system.

If your buried line drains back, likely no reason you couldn't use it to fill tanks in the winter.

NorthRick
Member
# Posted: 13 Sep 2021 12:26 - Edited by: NorthRick
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Quoting: ICC
Insulating a buried water line will not prevent it freezing. Insulation only slows the movement of heat. It does not stop the movement of heat. Heat always moves from the warmer place to the colder place, until both places are the same temperature.


Properly done, yes insulating a buried water line will prevent it from freezing. We do that here in Alaska all the time when you can't reach the ideal burial depth for whatever reason.

For the OP, 6 inches of foam board insulation should work. However, it needs to extend about 2 to 3 feet either side of your line. That will be difficult hand digging in the conditions you describe.

A drain back system like others have suggested is probably your best bet.

You don't need the conduit, just bury the water pipe. Another option depending on your electrical power situation is to bury heat trace next to the line.

Dom08
Member
# Posted: 13 Sep 2021 12:46
Reply 


Reason for the conduit for the waterline was allowing more air space around the water line so its not sitting against the cold geound/insulation. And if i blow a line i can fish another line down.

For a drain back system, water wouldn't be 'on demand' as that whole line would need to fill back up and supply the tap. I wanted to get away from a holding tank as well as i dont have much room for a tank to fit.

gcrank1
Member
# Posted: 13 Sep 2021 13:01 - Edited by: gcrank1
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Im afraid the reality is that under your circumstances your plan is expensive, labor intensive and won't work as well as you hope.....
I suggest you make it a drain-back system, conduit if you like (I like the idea of 'what if' in the future) and use a holding tank (even a smallish one under a counter or even overhead) with an easy drain also.
Pump the tank full as needed and have a small usage pump (rv type) at the tank to provide water at pressure to your fixtures. If it is overhead you may have enough pressure without a tank pump.

Irrigation Guy
Member
# Posted: 13 Sep 2021 20:20
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I am not sure of the freeze potential with a drain back system where the pipe meets the water line of the lake. It might freeze, maybe a bit of heat tape there? Mine drains back into the well casing below the frost line so it is not an issue.

DaveBell
Member
# Posted: 13 Sep 2021 22:07
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Rain water harvesting during summer to an underground cistern?

travellerw
Member
# Posted: 13 Sep 2021 22:12
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Have you looked into a pressure tank for storage? You can get them in all sizes. We have a 5 gallon tank in our RV that fits under the bathroom sink. It provides about 1.5 min of pressure before our pump kicks in. However, that can be set depending on how low of pressure you want before your pump kicks in

That way you would have on-demand water and a drain back system.

Dom08
Member
# Posted: 14 Sep 2021 09:19
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The only other potential issue i see will be the filter system we will have for the lake water. Its going to be pretty indepth.
I am going to try the insulation. If that fails ill run heat trace internal heat line to prevent freezing water supply lines

BRADISH
Member
# Posted: 14 Sep 2021 16:57
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Quoting: NorthRick
For the OP, 6 inches of foam board insulation should work. However, it needs to extend about 2 to 3 feet either side of your line. That will be difficult hand digging in the conditions you describe.

NorthRick's point should not be underestimated. The insulation needs to span well past the actual sides of your line, as the cold will bleed around the insulation.

Dom08
Member
# Posted: 16 Sep 2021 14:20
Reply 


Is it best to place fill around the lines and than add insulation?

Is sand a good insulator or dirt better?

Aklogcabin
Member
# Posted: 17 Sep 2021 10:15
Reply 


Place a couple inches of rigid foam board insulation over it. The rigid insulation also diverts rainwater away. I usually put black tar paper over it also. Laid in so water drains out n away.
Since it's already going down hill can you use an air compressor n blow it out in the fall before freeze up.
Good luck

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