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Old 09-26-2012, 01:46 AM   #1
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Dividing Concrete Slab Into 2 Sections?


I'll be building a small house out in the country soon and I'm in the planning and information-gathering process. I've decided for cost purposes, I will probably be building on a concrete slab.

I will be installing a septic system and the septic tank will be in the front of my house and the one toilet in the house will be in the back so I'll need to run the pipe from the back to the front and it will be running pretty much right down the middle of the house.

Of course I'm concerned about maintenance when I have a pipe running entirely under my slab...that would be a total nightmare to deal with should I need to access the pipe. So I got this crazy idea: What if I divided the slab into 2 separate sections with a gap in the middle where the pipe will run in between the two sections. I guess I'd frame out that gap and put whatever type of wood would be necessary to close the gap and just put carpeting/tiling over it like nothing happened.

So my question is: is this at all practical? The other plumbing would be connected to a gray water system which would directed to my rather large garden in the back, so it's just the toilet pipe that is the real concern.

All opinions and advice are appreciated

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Old 09-26-2012, 03:09 AM   #2
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Dividing Concrete Slab Into 2 Sections?


That might be a case of the tail wagging the dog.
If the slab is to be stuctural, you would be compromising its integrity by splitting it for the sake of a pipe. This could lead to differential settlement which would affect the structure.
As you are in the process of designing your house, now is the time to 'design out' potential problems.

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Old 09-26-2012, 08:30 AM   #3
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Dividing Concrete Slab Into 2 Sections?


That would be a sure way to have sidng and sheetrock issues from day one.
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Old 09-26-2012, 10:20 AM   #4
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Dividing Concrete Slab Into 2 Sections?


you could run a larger diameter pipe from the front to the bathroom and install your smaller diameter pipe for the toilet inside it it. Now should you have issues with the pipe you'd only have to break up the slab within the bathroom, cut off the fittings and pull the pipe out. Then follow the procedure in reverse. Once connected and operating properly place some new concrete and you're back in business.

I would not do as your propose for the reasons already stated by joe and tony.g
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Old 09-26-2012, 12:22 PM   #5
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Dividing Concrete Slab Into 2 Sections?


" larger diameter pipe... smaller diameter pipe... inside" Ingenious! The kind of screwy idea I would come up with. Except this one would actually work. Its a sorta resin pipe relining in advance.


Griff, I strongly recommend you reconsider the whole slab foundation idea as well as rerouting the toilet drain. Get out from under house as quick as you can. Use two 45 els at corners and clean out as close to toilet as you can, a two way clean out at corner from line along outside of house to tank.

Slabs are used because they are inexpensive, no, cheap, depending on soil, temperature, and drought conditions in your area ( which is ?) and soil prep, you could be letting yourself in for future nightmares and even disasters. There are other problems with slabs, some of which mite just be annoyances. One you are aware of, access to utilities underneath for maintenance or adding new. new plumbing may be in attic where leak could cause major damage. Your channel idea would work with extra thick slab and channel through it. (My mind(?) is drawing blank. What is name of such channel, for A/C lines etc. Stupid brain wants to say transom.) Jack hammering, sawing is expensive and messy.

Slab can be cold, costs of insulation under and around brings it up to or past other foundations. Slab is hard even under flooring. Difficulty in applying some flooring.
Shifting or cracked foundation can break plumbing. cracks bleed through flooring. Leveling, repairing cracked slab, harder, costlier than others

Kwik search found cost comparison of 32'x40' foundations from 2007, Spread between slab and costliest listed is less than $1000. Don't know location of costs. More intensive search mite find more up to date and localized info. I've lived on slab for 30+ years, was basically unfamiliar with them when moved here,raised foundations more common where I was raised. If I knew then what i know now, wouldn't have moved in.

What ever foundation, run drain outside of house, with plenty of clean outs. Not much more expensive, easier to get to if needed, even if drain suspended in crawl space. Costs now could be more than offset later.

Commend you on use of gray water, there's an expense, two drain systems. But savings for years to come. Be sure to install grease trap in line B4 cistern.
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Old 09-26-2012, 01:07 PM   #6
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I appreciate everyone setting me straight on this. I had a feeling there would be some structural issue but I was hoping I was wrong.

notmrjohn, my new property is in Campbell, TX which is just about an hour east of Mesquite. I currently live in Garland. I like the idea of running the piping out of the house. It makes much more sense.

As for type of foundation, I researched other options such as crawlspace and read negative things about that also. I'm not really sure which foundation would be best.

My soil type is Sandy Loam which I believe is much better for foundation compared to the usual clay soil that is found in much of our area. I found an online map showing soil types by area and the risk of using slab for each (link below). All people that I've known who've had foundation problems their home are located in the "red zone" which is high risk. All people who've had no problems that i know are in the "yellow zone". I guess in our area there is no green zones. Since my property is in yellow I figured it would be ok. Not sure now though.

http://websoilsurvey.nrcs.usda.gov/a...oilSurvey.aspx
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Old 09-26-2012, 04:29 PM   #7
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Dividing Concrete Slab Into 2 Sections?


Griff, 1st thanks for that link, its in favorites now. I had a book with all that stuff for Dallas County, soil, bedrock, maps, aerial photos all kinds of stuff. Few houses down street from me bedrock and sub-soil change. Loaned book out......" Lost, strayed, or stolen. Book about dirt, green cover. No reward.

I know Cambell. Yup, I'm on the Gumbo. Time lapse film of my house over years wet and dry cycles would be a true "moving picture." Right now is gap between "lawn" and curb 6"+wide past arm depth. When, if, it rains, soil bulges up higher than curb.

Pluses and minuses on all foundations. If foundation settles on raised ones, often can just jack and support small areas. I've seen old circular saw blades used as shims on concrete posts. Slab foundations often require Nolan Ryan and patented foundation leveling. I do like being able to get to things under house, instead of ripping up slabs. Wonder if you can call Nolan or other repair companies, ask them what types have most repairs in Cambell area. Ask nearby neighbors, too?

Between my last post and this I have had to go rent sewer cleaning machine. Box elder tree, cast iron pipe, under slab. " I like the idea of running the piping out of the house." And clean outs. Like clamps, you can never have enough. Two ways at corners. This house had none, except in main out front. I put one at box elder site. Oddly enough, while I was working away. Plumber shows up at box elder owning neighbor's house. Absolutly no clean outs at his house. plumber on roof trying to go down stack, no luck. Takes out toilet, no luck. They're debating now, take out wall behind toilet, lift stack and try there. Or knock hole thru brick, lift stack, try from that side then install clean out. plumber is even saying may need to dig hole get down to drum trap and go from there.I may luck out, neighbor may finally decide that the box elder has got to go. I just grinned as I put cover back on clean out and loaded up machine to take back. I may luck out, neighbor may finally decide that the box elder has got to go.
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Last edited by notmrjohn; 09-26-2012 at 04:37 PM.
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Old 09-26-2012, 05:20 PM   #8
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Dividing Concrete Slab Into 2 Sections?


Unfortunately generalized soil maps are useful mainly for rough planning, and cannot take the place of a site specific soil evaluation, which normally means either a soil boring, or more commonly excavation of a couple of test pits using a backhole. A qualified, experienced individual, sometimes an engineer, sometimes a soil technician, examines the soil and can tell you specifically if you have an expansive soil problem. The recommended foundation type for a specific location is dependent on the type of soil, you will need a very different foundation type on sandy loam than on expansive clay, and I would not assume that just because you are in a particular zone on a generalized map that your specific site is OK.

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