Tub and shower trap in concrete slab sitting on bedrock (ledge)

[John Gayewski]

Thanks for the further info, it all sounds good except for the above. The gravel inside the thermal envelope would just add thermal mass, like the concrete slab does. It wouldn't increase or decrease heat loss.

I actually had a similar response typed out. I decided not to post as I was hoping this thread would die. A heating pro would be pulling his hair out by now, luckily I don't have much left and can't afford to loose anymore.

 

[John Gayewski]

You can tell someone doesn't want to be helped when they say "I've done this (it) before" or "I have many years experience".

 

[Sponsor]

 

[Ed Dooley]

It would increase heat load a bit though, and with radiant heating the insulation wants to be right below, with the tubing inside the slab. We're covered as far as continuous insulation. here's a rough sketch of how we do it.

 

[Ed Dooley]

You can tell someone doesn't want to be helped when they say "I've done this (it) before" or "I have many years experience".

I don't know why you would say that, I do have many years of experience as a contractor in cold-climate Vermont. I asked for help with something I've never had to do before, a p-trap under a slab right on top of surface bedrock. You don't seem to understand how sub-zero cold travels laterally through bedrock near the surface, so not much help. Others have confirmed what I thought and I'm grateful for their advice. They helped me.

 

[Ed Dooley]

I actually had a similar response typed out. I decided not to post as I was hoping this thread would die. A heating pro would be pulling his hair out by now, luckily I don't have much left and can't afford to loose anymore.

BTW, my nephew is a local plumber, an acquaintance owns the largest plumbing company is my county, and I've used one other plumbing company on major projects, not one of them has had to do what I want to do, and none had an answer other than an insulated box around the traps, and they all understand how surface bedrock is a unique problem. Oh, and none of them were pulling their hair out discussing this.

 

[Jeff H Young]

maybe cut a channel in the rock to allow for foam around the plumbing. and so youll have 4 inches minimum under slab but leave the top open

 

[Ed Dooley]

Thanks, I’ve been seeing if both traps can go near the house wall, where it would be deep enough to insulate, but right now the plans puts one of them in the shallowest part and the other midway, both at an exterior wall. The bedrock is very soft sedimentary stone, and I have a lot of experience (there’s that evil word again!) cutting and drilling it. I’ve gone through a couple of angle grinders cutting grooves for power conduit to my other barn and other fun things, but it does cut easily, the dust killed them. Drilling, cutting, and pry bar leverage would make quick work out of it (without changing the trap’s location). Thanks again!

 

[John Gayewski]

I don't know why you would say that, I do have many years of experience as a contractor in cold-climate Vermont. I asked for help with something I've never had to do before, a p-trap under a slab right on top of surface bedrock. You don't seem to understand how sub-zero cold travels laterally through bedrock near the surface, so not much help. Others have confirmed what I thought and I'm grateful for their advice. They helped me.

I want this thread to die. The numbers don't add up like I said.

 

[Jeff H Young]

great in which case no biggie to channel it

 

[Ed Dooley]

I want this thread to die. The numbers don't add up like I said.

Don’t read it, scroll on by

 

[wwhitney]

It would increase heat load a bit though,

Only to the extent that the surface area grows a little. And if you have vertical insulation on the existing house exterior wall, that would be a minimal effect (for a very acute triangle, the difference between the hypotenuse and the long leg).

and with radiant heating the insulation wants to be right below, with the tubing inside the slab.

The radiant doesn't really care if there's thermal mass below it as well as above. However, I agree that it would be trouble to install tubing directly on top of the gravel, it's easier to staple it to foam. So you could consider splitting the insulation--2" on top of the bedrock, gravel to make a level surface, and then 2" of level insulation. But again, the only upside is to make it easier to insulate under the traps.

We're covered as far as continuous insulation. here's a rough sketch of how we do it.

Nice.

Cheers, Wayne

 

[wwhitney]

The numbers don't add up like I said.

I believe in this case you are mistaken, this is not a simple one dimensional problem. But to resolve this disagreement, either the OP would need to install some temperature sensors in his gravel and report back next winter, or we'd need some software to solve the heat equations for us and find the isotherms.

 

[John Gayewski]

I'm not mistaken. Your both assuming the surface temp doesn't degrade as you get deeper and assuming no heat from below and disregarding the fact that the trap isn't deep enough to freeze while leaving out the 70 degrees from above. It doesn't matter if there's foam above the 70 degree zone is it's constant 70 with 50 below. The - 20 intermittent short bursts aren't enough to overcome the constant 50 nor the constant 70. Not horizontally for a distance greater than a foot or so.

If the bedrock froze like that moisture would levitate the building.

I believe in this case you are mistaken, this is not a simple one dimensional problem. But to resolve this disagreement, either the OP would need to install some temperature sensors in his gravel and report back next winter, or we'd need some software to solve the heat equations for us and find the isotherms.

 

[Ed Dooley]

I'm not mistaken. Your both assuming the surface temp doesn't degrade as you get deeper and assuming no heat from below and disregarding the fact that the trap isn't deep enough to freeze while leaving out the 70 degrees from above. It doesn't matter if there's foam above the 70 degree zone is it's constant 70 with 50 below. The - 20 intermittent short bursts aren't enough to overcome the constant 50 nor the constant 70. Not horizontally for a distance greater than a foot or so.

There is no constant 50° near the surface of bedrock in a cold climate. There is no “deeper”, I’m building on surface bedrock, the “heat from below” doesn’t come to the surface. The 70° from above is blocked by the insulation under the slab. The mean temperature here in January is 16°, the above freezing temps 4-5’ down does not come near the surface. Your comment about no horizontal movement “for a distance greater than a foot or so” tells me you know nothing about cold climates or horizontal wing insulation to keep frost from getting under buildings. BTW, I thought you wanted this thread to die.

 

[John Gayewski]

There is no constant 50° near the surface of bedrock in a cold climate. There is no “deeper”, I’m building on surface bedrock, the “heat from below” doesn’t come to the surface. The 70° from above is blocked by the insulation under the slab. The mean temperature here in January is 16°, the above freezing temps 4-5’ down does not come near the surface. Your comment about no horizontal movement “for a distance greater than a foot or so” tells me you know nothing about cold climates or horizontal wing insulation to keep frost from getting under buildings. BTW, I thought you wanted this thread to die.

Ok Mr experience. Ice doesn't heave buildings? I don't live in cold climate? Just read more I guess.

 

[Ed Dooley]

Ok Mr experience. Ice doesn't heave buildings? I don't live in cold climate? Just read more I guess.

Frost doesn’t heave surface bedrock (unless you want to get really picky and talk about permafrost bedrock heaving), it’s not loose rocks, it’s solid rock, in this case from the surface down to the molten core. So no, frozen solid bedrock doesn’t heave buildings. Oh, one more thing, I’m done… now *I* want this thread to die.