My date for the Valentine's weekend

[1750]

https://www.hearth.com/talk/attachments/image-jpg.127626/

I spent a long day thawing out this drain line. It's surprising to me that it's only buried 8-10 inches. Now that it's uncovered I'm wondering how best to insulate it to reduce the likelihood of it freezing again.

Any suggestions on how to do this? Maybe just overlap some rigid foam insulation? And, the hole where it goes through the foundation wall is open. Should I fill this with expanding foam?

Thanks for your thoughts on this.

 

[DAKSY]

I'd run an electrical heat tape thru a conduit. I'd use something flexible, like a garden hose, that could be tightly wrapped around the PVC as that conduit. That way if the tape ever failed & they DO fail, you can pull a new piece thru when you withdraw the old one. It will also mean leaving access to both ends, but you could spooge a blob of silicone in there as a temporary plug for the opening. Just my .02...

 

[woodgeek]

Think how much heat a hot shower dumps in there. How many years before you had a problem? Put a couple inches of rigid foamboard over it, like XPS, rebury it and call it the next homeowners problem.

 

[1750]

I'd run an electrical heat tape thru a conduit. I'd use something flexible, like a garden hose, that could be tightly wrapped around the PVC as that conduit. That way if the tape ever failed & they DO fail, you can pull a new piece thru when you withdraw the old one. It will also mean leaving access to both ends, but you could spooge a blob of silicone in there as a temporary plug for the opening. Just my .02...

I was hoping to get protection I didn't have to plug in, but this would be a nice system to install in case I ever did have another problem.

Think how much heat a hot shower dumps in there. How many years before you had a problem? Put a couple inches of rigid foamboard over it, like XPS, rebury it and call it the next homeowners problem.

The system has only been in the ground two years, so I'm batting .500! It's at a cottage, so I think the infrequent use is probably the big problem.

I do think the rigid foam is probably what I'll do. Maybe build a 3-sided box out of it. Do you think I should foam the opening into the foundation wall, or is there some reason that should be left open?

Thanks to you both.

 

[woodgeek]

Agree about the infrequent use being an issue. I would second the tape suggestion then. I was thinking a flat sheet of foamboard a couple feet wide like a roof...use the thermal mass of the ground underneath, rather than a tight box with no soil inside. Prob work well with the tape.

Its prob stealing heat from your foundation, a good thing in this case. Run the foamboard all the way to the foundation wall. How cold does the cottage get when not in use?

I'd seal the pipe penetration myself, IMO wouldn't affect the freezing issue, but will prevent soil gases entering.

 

[1750]

We keep it about 45 when not there. I'll probably try and rig something right now to keep it from freezing and then when the ground thaws excavate a larger section and put the foam over it. Getting the soil thawed to dig is a lot of work. I get what you mean about a wider roof and not boxing it in. That makes good sense and will be easier to boot.

I'll probably have to clear out at least once more before I'm willing to run a heat tape to it permanently.

Thanks.

 

[begreen]

That is amazingly shallow for your area. Someone was taking a shortcut or thought of the place as a spring to fall cottage. Seems like it is just going to freeze further down the line until it gains some real depth.

 

[Highbeam]

That is amazingly shallow for your area. Someone was taking a shortcut or thought of the place as a spring to fall cottage. Seems like it is just going to freeze further down the line until it gains some real depth.

They may have been limited by a shallow septic tank or sewer hookup. You've just got to make it work sometimes.

 

[begreen]

Doesn't code establish the depth based on the frost line for the area? Not sure but I would expect it to.

 

[1750]

That is amazingly shallow for your area. Someone was taking a shortcut or thought of the place as a spring to fall cottage. Seems like it is just going to freeze further down the line until it gains some real depth.

They may have been limited by a shallow septic tank or sewer hookup. You've just got to make it work sometimes.

The builder said just what Highbeam said, that you have to set the tank and work backward. Apparently the design involves heat from the aerobic/anaerobic activity in the tank keeping the line warm.

I'll check on code requirements, but at this point the only way to address it would be to re-install the tanks and drain field and I can't imagine that happening.

I layered it from the clean out to the house with baled straw, 2" XPS, more straw, a big piece of Hardie board, and about 24" of new snow. I figure it's over R30 about now. In the spring I'll dig up the line to the tank and put a roof of the XPS over it.

Thanks to all of you for your suggestions.

 

[Highbeam]

The builder said just what Highbeam said, that you have to set the tank and work backward. Apparently the design involves heat from the aerobic/anaerobic activity in the tank keeping the line warm.

I'll check on code requirements, but at this point the only way to address it would be to re-install the tanks and drain field and I can't imagine that happening.

I layered it from the clean out to the house with baled straw, 2" XPS, more straw, a big piece of Hardie board, and about 24" of new snow. I figure it's over R30 about now. In the spring I'll dig up the line to the tank and put a roof of the XPS over it.

Thanks to all of you for your suggestions.

If the builder had worked backward properly he woul have raised your house a few feet and covered that line with fill.

 

[DickRussell]

Just for backup info on insulating that pipe, quoting from this source:
http://oikos.com/esb/43/foundations.html
"Insulation as required in this design guide will prevent underlying soil from freezing. Soil has an insulating value ranging between R-1 per foot and R-3 per foot. (Yes, these values are in feet, not inches.) An inch of polystyrene insulation, R-4.5, has an equivalent R-value of about 4 feet of soil on average." That equivalence seems to be using the lower R-1 value for soil.

With the pipe that shallow in the ground, a two-foot wide sheet of XPS will go only a foot to either side. That pipe (via measuring the photo) looks like it's around 30" or so from the house. You might want to provide frost protection for the pipe further out than a foot to each side, to maximize the distance between pipe and frozen ground. If you are digging up the pipe anyway in the spring, you could dig up from the house foundation, as woodgeek recommended, out four feet and cover that width with foam. That looks like a concrete block foundation wall. If the crawl space is closed off and you have the inside kept at 45, I doubt the ground in the crawl space (or full basement?) freezes. You'd be taking advantage of that heat loss to ground under the house in protecting the ground out four feet from freezing. If that's the corner of the house at the top of the photo, then heat from the crawl space is limited to the first few feet of pipe. But a four-foot width of foam over the pipe from there should do the trick. The other thing you might think of doing after the line thaws is to snake it out to the tank, in case there is some crud in there keeping the line from draining completely at present. Of course, water vapor from the tank could be frosting up the line back to the house. Just thinking out loud here.

 

[Highbeam]

How does insulating a frozen pipe in frozen ground thaw anything? Dont you need a heat source? Or does preventing heat loss with insulation result in warmer soil?

 

[DickRussell]

Well, yes, to a great extent trying to insulate now is closing the barn door after the horse has fled. Over time, by cutting off most of the heat loss to the winter air, the deep ground relative warmth will thaw the ground upward toward the pipe, and it would thaw. I think we're talking a post-thaw (spring time) project here, to protect the pipe next winter. Next year, the heat migrating upward from the ground to the bitter cold air will hit the insulation and a different temperature profile will be established, with above-freezing temperatures maintained up to the foam insulation layer, then taking a huge drop across that insulation to frozen ground above it. That foam layer will be the thermal equivalent of burying the pipe under multiple feet of additional soil, which is far more conductive than the foam.

 

[woodgeek]

I think Dick is saying that 1" of foam is like 4' of soil. If the frost line were 4' down in a given location, then a (wide) sheet of 1" foam just under the surface would keep what is underneath from freezing. This neglects thermal mass effects (of the 4' of soil) but is prob close enough if you double it, 2" of foam. I agree that the cold would sneak around the edge of the foam...DR's formula suggests how far.

 

[1750]

If the builder had worked backward properly he woul have raised your house a few feet and covered that line with fill.

the list of things this builder did not do properly is fairly lengthy.

Just for backup info on insulating that pipe, quoting from this source:
http://oikos.com/esb/43/foundations.html
"Insulation as required in this design guide will prevent underlying soil from freezing. Soil has an insulating value ranging between R-1 per foot and R-3 per foot. (Yes, these values are in feet, not inches.) An inch of polystyrene insulation, R-4.5, has an equivalent R-value of about 4 feet of soil on average." That equivalence seems to be using the lower R-1 value for soil.

With the pipe that shallow in the ground, a two-foot wide sheet of XPS will go only a foot to either side. That pipe (via measuring the photo) looks like it's around 30" or so from the house. You might want to provide frost protection for the pipe further out than a foot to each side, to maximize the distance between pipe and frozen ground. If you are digging up the pipe anyway in the spring, you could dig up from the house foundation, as woodgeek recommended, out four feet and cover that width with foam. That looks like a concrete block foundation wall. If the crawl space is closed off and you have the inside kept at 45, I doubt the ground in the crawl space (or full basement?) freezes. You'd be taking advantage of that heat loss to ground under the house in protecting the ground out four feet from freezing. If that's the corner of the house at the top of the photo, then heat from the crawl space is limited to the first few feet of pipe. But a four-foot width of foam over the pipe from there should do the trick. The other thing you might think of doing after the line thaws is to snake it out to the tank, in case there is some crud in there keeping the line from draining completely at present. Of course, water vapor from the tank could be frosting up the line back to the house. Just thinking out loud here.

This is a great link, Dick, thanks. It's astounding to me that soil is R1/ft. This soil is almost pure sand -- I don't know if that makes it better or worse. But that an inch of XPS would be the equivalent of 4ft of excavation is really remarkable. The foundation is poured concrete. This is the bottom level of the walkout, so there is nothing under it. I wonder if having them pour the slab on rigid foam reduces the heat loss near the foundation that might have kept this warm? I may have caused my own problem here. You are right, the clean out is about 3 ft from the foundation wall. In the spring I'll dig it out to the tank and add insulation to the line. I cleared the line with a garden hose and hot water all the way to the tank, so I think it's pretty clean at this point.

How does insulating a frozen pipe in frozen ground thaw anything? Dont you need a heat source? Or does preventing heat loss with insulation result in warmer soil?

I was hoping heat loss from the (uninsulated) foundation wall would keep this warm. I put a 3x4 sheet of insulation in there, so it's two feet on each side of the pipe. There's also supposed to be heat generated from the biological activity in the tank that travels of the pipe and keeps things from freezing. I was also hoping there is still heat migrating upward that would be tented by the foam.

Are you thinking this might not do the trick? That would be a bummer, as the sewage backing up into my mechanical room was a real unpleasant clean-up job.

Well, yes, to a great extent trying to insulate now is closing the barn door after the horse has fled. Over time, by cutting off most of the heat loss to the winter air, the deep ground relative warmth will thaw the ground upward toward the pipe, and it would thaw. I think we're talking a post-thaw (spring time) project here, to protect the pipe next winter. Next year, the heat migrating upward from the ground to the bitter cold air will hit the insulation and a different temperature profile will be established, with above-freezing temperatures maintained up to the foam insulation layer, then taking a huge drop across that insulation to frozen ground above it. That foam layer will be the thermal equivalent of burying the pipe under multiple feet of additional soil, which is far more conductive than the foam.

I think Dick is saying that 1" of foam is like 4' of soil. If the frost line were 4' down in a given location, then a (wide) sheet of 1" foam just under the surface would keep what is underneath from freezing. This neglects thermal mass effects (of the 4' of soil) but is prob close enough if you double it, 2" of foam. I agree that the cold would sneak around the edge of the foam...DR's formula suggests how far.

What if I boxed the pipe in? Do you think it would be better to have two horizontal feet over the pipe and a vertical foot on each side?

 

[btuser]

Check you main vent. If it gets clogged (snow, it can happen) it will slow down or even stop the warm draft that supposed to be coming from the tank.

 

[Highbeam]

Check you main vent. If it gets clogged (snow, it can happen) it will slow down or even stop the warm draft that supposed to be coming from the tank.

True for most but this is a limited use cottage with a very shallow tank and frozen ground. Depending on decomp heat for any help here is a bad idea.

 

[DickRussell]

..... It's astounding to me that soil is R1/ft. This soil is almost pure sand -- I don't know if that makes it better or worse. But that an inch of XPS would be the equivalent of 4ft of excavation is really remarkable......

What if I boxed the pipe in? Do you think it would be better to have two horizontal feet over the pipe and a vertical foot on each side?

The R value of soil does vary quite a bit, and it is much better for dry sand than for tight wet soil with a lot of fines. One source I found claimed that dry sand is about 0.6/inch, or about half as good as dry framing lumber. A tight, wet soil is more like 0.1/inch or less, making it more like the conductivity of concrete. So an inch of foam might be worth four feet of tight, wet soil or only seven inches of dry sand. For your situation, pick any number in between. So a 2" layer of foam probably is worth spending the small extra vs 1", given the effort of digging up the line in the first place. As to boxing in the pipe, making a sort of inverted "U" with the foam rather than laying the foam flat, I'm not sure I want to guess as to which is better, although I'm inclined to say I'd dig two feet to either side of the pipe and sloping down to the depth of the bottom of the pipe at the edges of the shallow trench, then lay the foam as a very shallow arch over the pipe. That might help divert surface water away from the pipe and let the sand stay drained.

 

[1750]

Thanks for taking the time to think through that, Dick. That seems like a simple and elegant plan.

The sand is easy to dig and it's only about 25 feet from that clean out to the tank. Three sheets of the 2" should get the job done.

I just hope we don't have it freeze-up again before our part of the world thaws.

Thanks again!

 

[Lake Girl]

When you mentioned that the tank was not down very low, I wondered if you had run into bedrock. Repositioning the tank would also mean repositioning the field. If you are going to be digging, you may want to expose your tank and field outlet to make sure you have proper gradients for all components. Once that is confirmed, you could add foam to the top of the tank also to retain heat longer and consider a berm over the tank and house outlet for more insulating protection. Make it a landscaping feature instead of a problem...

 

[1750]

No, it's not bedrock that I ran into, but governmental bureaucracy. The DEQ (dept of environmental quality) controls the area and I've subsequently found out required the line to be no more or less than 24" below finished grade. That established the depth for the tank. (I don't know why they are so particular about the depth, as we are up on a bluff and there is no issue related to the water table.)

The soil we are on is almost completely sand below a thin layer of topsoil (the ecosystem is referred to as "forest dune"). There was a little bit of washout, as nothing is holding the sand in place, which may have reduced the freeze protection. I think the foam plan that our friends here came up with will do the trick. I'll uncover the top of the tank and do that, too. I also think the depth of the frost penetration is pretty spectacular this year -- we have people losing water lines that are 5 and 6 feet below the surface.

I do think I will try and berm up the line and tank as you've suggested. Also, a good layer of mulch will help destabilize the soil and give the native plantings something to grab into.

Thanks for the suggestions!

 

[Lake Girl]

I would suspect that there are enough low areas in the state that concern for water table contamination lead to the blanket rule... to bad they don't take into consideration site specifics. Now that you have passed inspection, additional landscaping wouldn't hurt

 

[1750]

And I enjoy landscaping, so I will be doing that anyway.