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Old 01-26-2014, 12:00 AM   #1
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Plumbing in foundation slab


I am about to embark on my biggest DIY project to date.... building a garage/workshop/guest house from the ground up. I am intending on doing most of the work myself, hopefully the parts i am unsure about you guys can help me out with!!!

First issue I have is the plumbing in the foundation slab.

so it GENERALLY goes like this.

1 - Dig big hole
2 - Build Forms
3 - Backfill with gravel
4 - Compact gravel
5 - Add layer of sand
6 - Compact sand
7 - Add damp proof sheeting
8 - Add rebar
9 - Place concrete.

but i know i need to put some plumbing in my slab, so there are 2 questions.

1 - where do the pipes go? below the gravel? in the gravel? in the sand? in the concrete?

2 - where the pipes vertically penetrate the concrete (so i can connnect onto them in the house) do I need to protect the pipes in any way? or does the concrete come into direct contact with the pipe?

finally, I assume that whatever I do for in foundation plumbing, I can do the same for electrical conduit.

Thanks in advance for your help!!!

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Old 01-26-2014, 05:46 AM   #2
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Plumbing in foundation slab


Have you thought about putting any insulation in?

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Old 01-26-2014, 06:41 AM   #3
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Plumbing in foundation slab


I am located in Texas, USA. Insulation is not needed in the foundation here, but thanks for asking!!!

Anyone else feel free to comment on that, but i have been looking pretty closely (some may even say nosily!!!) whenever i go past any construction sites around here, and no one seems to bother with insulation.
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Old 01-26-2014, 06:47 AM   #4
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Plumbing in foundation slab


have you thought about the big hole you're digging for yourself ? oh - might be nice if you'd taken time to let anyone know just WHERE this garage/workshop/guest house from the ground up is to be located does make a difference in responses

before any waste their time, do you have the necessary skills/knowledge/desire/plans/permits to do this work ? or shall we anticipate many future threads ?

not so fast on the 1st issue - plumbing doesn't ' go ' in the slab - its either above OR below depending on certain factors - 1 more thing - why any sand - can't compact sand

just in case you've started digging already,,,,,,,,,,,,,,,,,,,,, vapor barrier's missing from your list best wishes !
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Old 01-26-2014, 06:51 AM   #5
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Plumbing in foundation slab


Please go back and add your location to your profile. Without knowing where you are on the planet it's hard to make the right suggestions.
Just go to quick links to edit.
Have you been to your local zoning dept. and health dept. to see if you can even get a permit for this yet? Adding another bedroom is going to going to be the biggest issue.

Adding insulation under the slab will make the floors warmer.
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Old 01-26-2014, 06:59 AM   #6
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Plumbing in foundation slab


Hire building the foundation and rough plumbing out.
Done wrong the rest of the building is useless.
Make sure the sides of the foundation raise the side walls at least 6" above finished grade to prevent water damage to the sheathing and siding.
Google "stem wall construction".
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Old 01-26-2014, 07:11 AM   #7
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Plumbing in foundation slab


You need a plumbing drawing----the drains and piping must be covered with crushed stone or gravel to a code specified depth---

where they penetrate the slab they will need a flexible sleeve--most plumbers use foam sleeves------

A licensed plumber will be along soon--if you know the code schedule used in your area that would help---
If this job will be done in a nonpermit part of the state---it still is important that you meet or exceed the code---the cost of failure is huge--so give us details and we will help.--Mike--
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Old 01-26-2014, 09:01 AM   #8
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Plumbing in foundation slab


Water supply is sleeved under compacted builder's sand full length from one stub out to the next, ( running ) with the least expensive 1-1/4" poly that can be purchased. Leave a foot extending above grade to be cut off before Pex is pulled.
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Old 01-26-2014, 09:44 AM   #9
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Plumbing in foundation slab


In answer to all of the questions

I am located about 50 miles outside of Austin, Texas, USA.

itsreallyconc :-

I have the skills, desire, plans and MOST of the knowledge. The missing part of the knowledge is what I am here for!!! Permits I am aware of, but dont have yet. It will not be a problem when the time comes.
SO the pipes don't go in the slab. and in my case they will go beneath the slab then, but WHERE? In the gravel? or below the gravel directly in the dirt? With regards to teh sand, it was just there to give a nice flat surface for the vapor barrier to sit on, and to prevent teh gravel from puncturing it when the concrete is placed. If the sand is not necessary, then it is one less step for me! Does any one have any comments/thoughts on the inclusion/exclusion of sand from a slab foundation?
Vapor barrier - I had it as item 7 on my list, its just a difference in terminology, but tat is what I meant.
Thanks for the well wishes, and for taking the time to post a comment!!!

joecaption :-
Location information updated.
Haven't been to zoning/health, but it will not be an issue. biggest problem will be getting the septic approved....
I will take the insulation into account before finally building.
I understand your point about subbing out the foundation/plumbing, but the reason I am on a DIY forum is so that I can get the information I need to make an INFORMED decision as to whether I will tackle it, or whether I will DIY it!!! I have built large industrial foundations in the past, and am trying to decide if I want to tackle this
I appreciate the comment about 6" above grade, and I will google stem walls.
Thanks for taking the time to post a comment!!!

oh'mike
I have the plumbing drawing so I know where the pipes need to be inside the house, just trying to figure out how to get them there!
SO, it seems that it is code that will determine where they go... anyone have any idea what code is in Texas? another trip to the bookstore is in order, but any help on where to look would be greatly appreciated!
I appreciate the rest of your comments. Thanks for taking the time to post a comment!!!
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Old 01-26-2014, 10:00 AM   #10
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Plumbing in foundation slab


Quote:
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Does any one have any comments/thoughts on the inclusion/exclusion of sand from a slab foundation?
Sand is used over hardcore in the UK to prevent damage to the DPM, but may not be used where you are.
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Old 01-26-2014, 10:01 AM   #11
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Plumbing in foundation slab


Are your questions with regard to DWV or supply? What material do you envision using for DWV and supply?

Quote:
Originally Posted by quantumkev View Post
where do the pipes go?
Depending on your layout the DWV go where your plans dictate in your gravel.


Quote:
Originally Posted by quantumkev View Post
where the pipes vertically penetrate the concrete (so i can connnect onto them in the house) do I need to protect the pipes in any way? or does the concrete come into direct contact with the pipe?
If you were to use a closet flange over the outside of your drain then you should protect the stub up with some foam wrap or something during concrete pour. If the flange is going on the inside of the drain then concrete touching the outside of PVC is not a big deal.

Are your question with regard to DWV or supply? What material do you envision using for DWV and supply?
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Old 01-27-2014, 09:42 PM   #12
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Plumbing in foundation slab


Below grade plumbing is not something a DIY'er should do.
Actually......anything more than connecting a sink or toilet.

What size is this workshop ?
The Austin area doesn't have to worry about frozen ground.......but with global warming you never know......lol.
So you probably don't have to worry about foundation walls below grade.
How big was this again ?

Always, when piping runs through a concrete floor sitting on the ground.......it needs a sleeve.
Even a wrap of poly around the drainpipe will work.......but for water you should have a sleeve.

Last edited by Gary Evans; 01-27-2014 at 11:31 PM.
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Old 01-27-2014, 10:28 PM   #13
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Plumbing in foundation slab


I'll tell you how we do ground roughs around my neck of the woods- you decide if they apply in your area.
The slab sub grade is usually graded to within a 10th of finished sub grade with approoved fill.
Plumbers then determine the needed grade and depth for the pipes. All pipes need to be below the slab, not in the slab, excluding the risers of course.
I have heard some areas require a certain amount of separation between concrete and the pipes. This info will come from your inspector.

Once the system is installed, it is tested with air or water and approved by the inspector.
Then it is back filled and compacted as needed. Then the pipes are wrapped with framers sill seal- 1 wrap on risers, 3 wraps on the water closets to allow for flanges. Water lines are treated basically the same.
No pipe should contact the concrete and allowance for movement is needed.

Vapor barriers, insulation, etc. after the plumbing is in the ground.
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Old 01-27-2014, 10:42 PM   #14
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Plumbing in foundation slab


There you go
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Old 01-27-2014, 11:05 PM   #15
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Plumbing in foundation slab


Take a look at some of the dozens of post on here in the past month about frozen pipes.
Places that have never had them freeze before are now having trouble.
Just make since to me to prevent all that by running all the plumbing through inside not outside walls when coming up with your plans.
Making sure your shower or tub control valve has an accessible panel behind it for service is also a good idea.
Any walls where large drains and supply's are run are a whole lot easier to work around if you use 2 X 6 walls, not 2 X 4's.

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