Insulating well water line on ledgy lot in climate zone 6…
We are building an energy efficient house in north-central NH (climate zone 6a). This question is a bit off topic, but hopefully someone might be able to help. The lot has shallow soil and there’s no way we can trench deep enough to get the well water line below the frost line…and it’s very likely that in extended sections we’ll only be able to dig 1′ or so.
We’d like to avoid rock hammering (damage to already poured slab?) or rock trenching because of expense and other reasons. We feel pretty confident that we can protect the line by:
-burying as deep as possible
-insulating with rigid foam boards
-add fill on top
-run heat tape
But I’d love to hear some real world examples of people doing this in the Northeast and other cold climates, partially to ease our minds and help convince our building inspector. Has anyone worked on a house or have a house with shallow well lines that you’ve successfully kept running in winter with these techniques?
Thanks for the help,
Brian
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Replies
Brian,
Ideally, you don't want to depend on heat tape or any method that will require extra pumping energy. If you can manage to get 2 feet of soil above your pipe, and you install XPS above the pipe that is less than 3 feet deep -- I have used 2 inch XPS, 2 feet wide -- I think you'll be OK.
They make a particular insulation, foam with a white plastic jacket for this application. Comes pretty thick.
Run heat 'cable' never heat 'tape'. The stuff with the braided metal cover.
I ran my city water line wrapped in regular hardware store pipe insulation with a piece of 4 inch iso foam[that there were leftovers sitting around] laying OVER the pipe, NOT under. and while backfilled there was basically no dirt over it. Turned on the heat cable in october. and it never froze. Today i would use EPS/XPS with pressure treated plywood above to protect it. The ledge does not really freeze, so you need to prevent heat from escaping up.
Where it got deeper it had only the regular foam insulation and heat cable, that was never turned on. We mounded dirt to get about 2 feet over it.
Never had a freezup.
WE also used copper line on the suggestion of the excavation contractor, since the whole length from the street was marginal, in case of a freezup it would be thawed with a welder, or so he said.
I have a little experience in this, because I have similar problem. I'd run three separate lines of heat tape, because these are known to fail. Wrap it around the pipe and then insulate the pipes with pipe insulation.
Try to set it up so that the well pump discharge can drain back. Standard system don't, in order to save pumping energy. It takes a lot of electricity to pump water up, but if the water table is high, it may be acceptable, since it's the only fail-safe method.
You can study the principles of FPSF, which aims for a similar goal of preventing underground water from freezing by using XPS rigid boards: http://oikos.com/esb/43/foundations.html
I'll second the copper pipe suggestion, even though PEX is freeze tolerant. You can melt the ice by applying 40 amps or so of current from a welder, which we had to do several times last winter.
Another thing I wish I had done is run two pipes. That gives you a backup, and an opportunity to recirculate the water thru the water heater if necessary.
I agree with Martin. XPS is the way to go. I work for a municipality in eastern Canada and anywhere we have waterlines above the frost depth we require 1" of XPS per foot above the frost line. If it was my house I would add an additional inch to the calculation to be on the safe side. The last thing you want to do is dig up a frozen water line in the middle of January because you didn't add enough insulation.