I have an underground p trap for my tub, how to prevent it from freezing?

[amodoko]

Hi guys, I have a condo that is built on a slab and am currently installing the plumbing to a new tub. There is no access to my p trap once a tub is in place due to the house being on a slab. Below the slab is about 13 feet of open space, so the p-trap will just be exposed to the air that is enclosed under my home. This air is not temperature controlled and is basically the temperature it is outside except that it is surrounded by cement walls. I am worried about the water freezing in the p trap during the cold winter months (temperatures can reach 0 degrees F here in the midwest at times), or the frigid temperatures cracking my pvc cement bonds. I don't know if this is possible, but I was concerned about it.

My questions are: Will the water freeze in my schedule 40 pvc p trap if the tub is not used more than once a month, even though my heat is on inside the condo? Do I need to put pipe insulation around the p trap or is this unnecessary? Do I need to actually go down there and insulate the cement walls to keep the temperature warmer in there? Or do I need to buy some heating device, like heat tape?

Thanks, just trying to figure out how my plumbing will be okay if there is no insulation down there since it can be so cold. I appreciate the help

 

[phishfood]

I don't have a authoritative answer, considering that I don't experience those kinds of temperatures in my area.

But it would seem to me that if you haven't had trouble with this in the past, it shouldn't be a problem going forward.

 

[johnjh2o]

I am really confused about this tub install. I went through a long lengthy post giving instructions on how to set up the tub waste so the tub could be dropped onto it because you said there was no access to it. Now your saying there is 13' of space below it. If that is the case then you could just set the tub and install the waste and overflow from below. There have been many threads on this install. At this point I think were all being had.

John

 

[amodoko]

Okay thanks guys, I appreciate it. Sorry John, I guess what I meant to say in an earlier post is the 13ft space below it is into the earth. Like, it is a cavity in the soil, but the soil doesn't start till you go 13ft below. I've posted some pics of that to show you what I meant. The only stuff down there is what looks like left over parts from the construction of the house (lumber, insulation peeling off the cement walls, etc). But once a tub is installed I can't get out of it without jack hammering another hole into my slab, which I didn't want to do initially because I would then have to repair the second hole. The first hole I made was just where the waste/overflow goes.

If there is an underground access to my condo, I haven't found it yet, so that is why I felt I had to fit the waste/overflow to the tub first, then take measurements to fit it to my old plumbing so the new tub would fit to it when I slide it in.

I have posted a ton of questions, and I apologize if I have frustrated anyone. I just have a lot of time to get this job done, and as I progress further I think of more questions. This is my biggest home repair, and I just want to do it right.

But I appreciate all your guys' help thus far, I'm really just fine tuning a few of my thoughts on what I want to do, and the whole "freezing" issue came up in my mind. The p trap never froze before because that tub was literally being used 3 times a day. I was more concerned about when my roommate eventually moves out, the tub will only be used once in a while because there is another shower in the condo that is used more frequently.

But anyways, sorry if I upset you John, I am extremely meticulous about everything in life, especially if I don't understand something... I will ask a lot of questions. But anyways, thanks for all your help thus far, I do appreciate it.

 

[johnjh2o]

Sorry foe the miss understanding. That is some mess under there. I would think there should be some access to it as there is a clean out in the line. I can't imagine installing a clean out with no way to get to it. As far a freezing it shouldn't be a problem. 13' is well below the frost line. The entire area would be just like a large thermos bottle with the heat source being the warm earth at 13'. If you can find the excess to the area it will make the tub install a lot easier.

John

 

[amodoko]

Hey John, no worries about the misunderstanding, but I'll also try to post fewer questions about this topic since I know I do ask a lot of questions. But anyways, I had tried a week ago to find another access to my condo and couldn't. Then today, I asked my neighbors by me if they would mind me snooping around their place for an access, and they didn't mind. I actually found an access under each of their condos! The first one I tried didn't go to my home, it had a dead end. The second one though.... after some snooping around, I found my home! So my neighbor and I share one access, I didn't know that was possible. This really will make my job a ton easier.

As far as the freezing goes, now that I was actually down there, I saw that it is only like 5 feet deep, it looked so much deeper from the view above though. I don't think it should freeze though since the whole area under my condo is enclosed by cement except for the one access. Although it is not temperature controlled, it is an enclosed area, so that will help resist freezing I think. And I'm assuming my floors will lose some heat to the area under my condo, kind of like heating it a bit. So it will be cold, but I don't know if it will be cold enough down below to freeze the pipes. But I may just put some pipe insulation on the trap to be safe, and when I'm not using it for an extended period I may pour some antifreeze down there to prevent it from freezing.