plumbing placement in monolithic slab

[dlukas]

I'm building a small detached MIL unit (22' x 15') in my back yard, with a 3/4 bath and full kitchen. Other than shower and toilet drain, all of the rough-in plumbing will be located in exterior walls. I would prefer the foundation to be a monolithic slab with thickened edges (rather than a spread footing with stem wall). This is mainly for cost savings--having to order three separate pours, each with a service fee and a partial load charge, will more than double my cost of concrete relative to a single pour.

However, I'm being told that contractors prefer the footing to be in place first, because it's easier to place the utilities accurately.

Why is that, and how different is it, really? It seems like if the forms are in place, it should be no problem to see where the pipes should be. Everything is ABS and PEX, and my plumbing wall will be 2x6 framing, so there's some margin for error, as well. Thanks all!

 

[johnjh2o]

90% of the single family homes are done with monolithic down here.

 

[frodo]

the footers are dug using a machine. when they try and dig it after the pipes are installed, they get tore up
are in the way. get bumped out of the wall.etc etc etc

it works out to everyones benefit.

frame the batter boards
dig the footers
install the plumbing

just the way its done, a system that works


a wall is 3.5 '' wide a pipe is 2.5



that is to scale. just to give you a visual.

I am responsible that the pipe is in that wall, if it is not in the wall, the money to put it their is my responsibility
the ditch digger, does not give a damn if he bumps it.



does this make it clearer ?. to move that pipe over, because it was bumped

involves breaking concrete and a pissed off homeowner with a hole in a new slab

thats why

 

[dlukas]

when they try and dig it after the pipes are installed, they get tore up

frame the batter boards
dig the footers
install the plumbing

This is exactly consistent with what I said, i.e., excavate, backfill, build forms, run plumbing, lay vapor barrier and rebar. At no point did I suggest installing the plumbing before excavating.

a wall is 3.5 '' wide a pipe is 2.5

My plumbing wall will be 2x6 framing, so more wiggle room than your assumption. I feel like I just need to make sure that my forms are square, and that my stubbed-up plumbing emerges between 1"-2" of the edge of the form, right?

Also, what I'm really curious about is how that is any different from a spread footing + stem wall foundation. You still have to locate your plumbing within the forms just as accurately, right?

 

[Mr_David]

I'm building a small detached MIL unit (22' x 15') in my back yard, with a 3/4 bath and full kitchen. Other than shower and toilet drain, all of the rough-in plumbing will be located in exterior walls. I would prefer the foundation to be a monolithic slab with thickened edges (rather than a spread footing with stem wall).

Mono slab with thickened edges. That is a small structure but you still need proper load bearing footing for the Main walls. Don't really need footings for the interior wall unless they are load bearing.

Slab design can be critical to your soil and weather conditions as well.
They use post tension slabs when they build on fill that is unstable to prevent cracked slabs.

Monolithic pours are common around here as well.
Chalk the ground for footings.
Dig out footings.
Set forms.
Set underground plumbing.
Back fill.
Add vapor barrier.
Cover barrier with sand or clean fill.
Set your rebar and wire.
Pour it.

 

[Mr_David]

Don't forget the anchor bolts for the wall

 

[frodo]

It can be done any way you want to do it.

I have roughed in buildings with nothing more than 2 strings up.
in an open field.

as long as you have 2 points. to measure off of. you are good to go.

I personally, do not like taking the risk of having ditch diggers and machines coming in after me.

I have seen to many times the broken crap they leave behind.

I prefer to rough my plumbing in after ditches are dug.


you asked about stem walls. they build the walls, pour them, demo the forms, then bag the corners back fill

i come in after them