Roughing in electrical/plumbing in slab

[wonderplumb]

People with showers and toilets on concrete slabs are in trouble then. If a 25mm conduit weakens a slab, imagine what a 100mm poo pipe would do.

And this is the reason I said to run it in the ground UNDER the slab, I dont know about conduit but any drainage or water pipe requires 25mm minimum cover under a slab, ie under the bottom of it. Except of course where it passes through the slab (risers etc.)

[Ashes]

That is what I thought as well. I guess the difference here is that the electrical conduit would run very close to the edge of the slab. I probably wasn't clear with my comments on running conduit in the slab. I would definately run it from under the slab and up as apposed to embedding pipes horizontally in the slab.

[Honorary Bloke]

Even in the days when plumbing was run under the slab, electric service (over here) was always brought in next to the slab and run in the walls, attic, and down (except for those very rare GPOs in the floor). There is no need to do it.

[journeyman Mick]

Running it next to the slab and up through the corrugations is a good move though, because less slab penetrations = less potential termite entry points.

Mick

[silentC]

That is what I thought as well. I guess the difference here is that the electrical conduit would run very close to the edge of the slab. I probably wasn't clear with my comments on running conduit in the slab. I would definately run it from under the slab and up as apposed to embedding pipes horizontally in the slab.

Well yeah, that goes without saying. I can't imagine why anyone would want to run it horizontally through the slab. You dig a trench, put the horizontal pipes in it with risers, and then pour your slab.

Toilets are very often right at the edge of the slab, I'm not aware of anyone having problems with the slab being weakened as a result. Mine is about 200mm in from the edge and guess what? After 3 years, the shed's still here! No catastrophic failure of the slab.

EDIT: my electricals come up through the slab right at the edge too. The only thing that doesn't is the water, which comes through the wall.

[Honorary Bloke]

Toilets are very often right at the edge of the slab, I'm not aware of anyone having problems with the slab being weakened as a result. Mine is about 200mm in from the edge and guess what? After 3 years, the shed's still here! No catastrophic failure of the slab.

A dunny in the shed, Silent? Real men just use their cyclone bucket.

[silentC]

But where do you go when you want to read the latest edition of... err... Fishing World?

[wdyte_dan]

in theory it may weaken the slab true if the conduits are run very close the edge of the slab, which is what they may have been talking about, but for the main a small pipe won't do much damage. If anything, if will reinforce the concrete!

Power/water coming in could easily be run up the side of the shed. But drainage really should be put in the slab or you will be running 100mm pvc all over your shed and it will look horrible.

[silentC]

OK let's get technical for a minute. Now my shed consists of five portal frames clad in colorbond steel. The slab has a thickened edge and some beams that run through the guts. The footings for the portal frames are cast into the slab. There is a footing at each corner of the slab and three equally spaced down each of the long sides. This is the only point of contact between the structural frame and the slab. The wall sheets contact the edge of the slab around the perimeter but this is incidental. These sheds can be erected on pads with no slab at all.

Now, if I put a 100mm PVC poo pipe 200mm from an edge of the slab, in what way is this going to 'weaken' it? There is mesh around the penetration and there is bar running along the edge of the slab between the pipe and the edge. Not to mention trench mesh under that. I'm at a loss to work out how this can have any detrimental affect on the slab whatsoever. Possibly the worst thing that is going to happen is that it will crack. In fact you show me a slab that doesn't have any cracks in it. That's one of the reasons we put rio in.

I think that making these kinds of claims (and I'm not directing this at you wdyte_dan (Warrandyte?)) just causes people to fret about things that they shouldn't and maybe do things that are unnecessary based on a myth.

Just about every house on a slab that has a toilet must have at least one 100mm pipe through the slab within a couple of hundred mm of the slab edge, because toilets are usually placed on an external wall under a window. Likewise for kitchen sinks. How often do you see a toilet in the middle of the room?

So unless we have a structural engineer here who can provide evidence that placing pipe penetrations near a wall has a detrimental affect on the building, let's have no more nonsense about it

[Ashes]

I'm only anticipating having 1 drain for a laundry unit type cabinet/sink so if I have to, running it out the back wall of the shed shouldn't be too bad.

I suspect the comment about weakening the slab is more based around it being a hastle to co-ordinate 2 blokes..

My next question shows how much of a sparky I'm not so please be gentle..

I intend on having around 15 double points, 8-10 double batten flouros, 3 or 4 sets of track lighting (each 2 or 3 globes) on dimmers.

What cabling is likely to come in to support that wiring requirement? Will it come in via a single mains cable or multiple cables?

[silentC]

I'm no sparky either, but based on the experience with my shed, assuming the sparky puts a sub-board in the shed, there would only be one cable coming in and an earth wire going out.

[dan76]

"they recommend that normally power conduit is run up next to the slab and up one of the ridges in the colorbond"

cant quote a clause number off top of my head but i have a memory of not being able run a cable under roof sheet ,wall sheet, etc between it and what it is fixed to. too easy to screw through.
i have not being doing ot for so long ive forgotten if it is a rule or just good workmanship lol

[bricks]

If you can the usual way to do thing is to start by select where you want the riser of your conduit or pipe to be and then work out a way to get out of the slab area in the shortest distance possible.

When installing in the edge of a slab the corner bars on the reo cage should be on the outside of the pipe relative to the slab.

If there is no corner bar between the pipe and the edge of the slab it may crack away.

[wdyte_dan]

I think that making these kinds of claims (and I'm not directing this at you wdyte_dan (Warrandyte?)) just causes people to fret about things that they shouldn't and maybe do things that are unnecessary based on a myth.

Totally agree. Suppose I was getting at that 'in theory' it would weaken the slab, some mathematical formula would dictate that removing a single stone from the aggregate could weaken it ten poofteenths of a percent - but it's just not measureable! shed installer sounds like he CBF'd dealing with the requirements of the customer

[joe greiner]

So unless we have a structural engineer here who can provide evidence that placing pipe penetrations near a wall has a detrimental affect on the building, let's have no more nonsense about it

Slab penetrations near the edge should have negligible detriment if the clear distance is about 1.5 times the thickness of the slab, with reo between the penetration and the edge. Piping placed horizontally will be detrimental if it's close to either top or bottom surface; if placed at the mid-plane of the slab, no sweat, but not easy to control - probably best to place below the slab.

To preserve options for future placement of in-floor power points, it may be advisable (and generally cheap enough) to place a few additional empty conduits with sealed plugs at both ends.

Joe (PE, SE)