Roughing in electrical/plumbing in slab

[Ashes]

Hopefully a question the sparkies and plumbers can answer quickly. I haven't done this before so not sure of the answer.

I'm probably 4 or 5 weeks away from putting the slab down for my shed. I'd like to have the electric conduit and water/drain run through the slab instead of through the wall. I haven't organised a sparky or plumber as yet.

Who would normally organise the putting in of the conduit/drains when the slab is being formed up or poured? Who do I need to organise and when for this work to be done?

I'm looking to have conduit run in for electricity. 2 or 3 in floor mounted powerpoints (in the middle of the workarea with covers). Looking to run mains water in and a drain for a sink going out.

[journeyman Mick]

Usually roughed in by the plumber/sparky who is doing the rest of the job. I'd be wary about running the water supply in the slab, avoid it unless the water needs to come out of the floor well away from any walls. I've seen literally 100's of places that were built in teh 70s and 80s where in slab water pipes have started leaking and have had to be replaced with retrofitted pipes. All the newer places have minimal supply lines in the slab (avoided unless absolutely neccesary). They are run in the ceiling and down inside wall cavitys instead. Where they are run through the slab both hot and cold lines must be in lagged copper to prevent the movement of the pipes rubbing holes in the pipes.

Mick

[Honorary Bloke]

What Mick said. They ran plumbing through the slab for dog's ages and now they are reaping the whirlwind. Modern practice is to run in the ceiling and drop to needed locations.

A couple of electrical outlets in the floor might be a good idea, though. Your sparky will know what conduit to run.

[wonderplumb]

It can be done, though not desirable. If you must do it this way, try to scratch it in the soil under the slab, try to do it in one continuous length with no joins, have your turn up done with a pulled bend rather that a soldered one and make sure its lagged.

[Ashes]

The water/drain access is actually at the rear of the shed and won't be seen so I might just take the easier option of running the water and drain through the wall.

Does the sparky come in before/after it is formed up. Guessing before if any trenching is required for cables?

So you'd suggest I start getting some sparky quotes now and lining one up. I think I might have an interesting mains cable run as my meter box is at the front of a 2 story home, and the shed is at the back of the yard. Probably a 30m run with a house in the way!

[DJ’s Timber]

Do you have access under the house? My cables were run under the house to the nearest point to the shed then in to a trench as shown here (http://www.woodworkforums.com/showpost.php?p=530170&postcount=78), but if your on a slab then you'll have to go in a trench all the way around the house :doh:.

[Honorary Bloke]

Does the sparky come in before/after it is formed up. Guessing before if any trenching is required for cables?

Yes. Before.

So you'd suggest I start getting some sparky quotes now and lining one up. I think I might have an interesting mains cable run as my meter box is at the front of a 2 story home, and the shed is at the back of the yard. Probably a 30m run with a house in the way!

I'd like to see a pic of that! :rolleyes: I just can't visualise it. Doesn't the power come from the street to a meter box on your house? :?

[rod1949]

I'd be incline to also bring the power down rather than up.

[Ashes]

A picture is worth a 1000 words...Looks like the best option is to dig a trench down the sideway (on the side the fuse box is). Under about 3m of pavers (big ones so hopefully can get away with pulling up just a few..Under the garden bed next to the pavers, avoiding the sprinkler system..across the back lawn (avoiding the main water line running to a tap and then into the shed. Probably a sewer line in the way as well...

The house is on a slab, so can't go under. It is a 2 story house so probably difficult running it in the ceiling

[wdyte_dan]

It is definitely easier to put the plumbing and electrics in prior to concrete, plumbing in particular in your case will be a major hassle post pour if it's not done right.

The only thing to consider is that there are Australian Standards to meet in terms of electrical and plumbing installations below ground, and it might pay to involve those who deal in the black arts/protected trades of electricity and plumbing to advise you early on how to do these things.

You have come up with a pretty good plan on your other thread, print it and give it to a sparky/plumber and ask them to advise on installing services. They may be comfortable with you doing a certain amount of the labour/installation as part of the job they will sign off, although some (esp sparkies) may not be as comfortable.

The plumbing could be about 90% done before your even poor the slab. The sparkies job will likey be easier as there is probably only going to be one entry point to the shed - if this is through the slab, you'll need to check with him to install the appriopriate conduit rising near the switchbox (Do you still want those in-floor power points?) Anyway, consult early!

[dan76]

mate , talk to the tradies and with the attitude you have of being planned out and having a clear idea of what you want the finished job to be i cant see you having any problems.

except maybe the prices lol

[patty]

The conduit on the inside of the wall is simple you just have to compensate for your wall/purling thickness on the slab and offset your conduit to be just on the outside of it.
Instead of having floor mounted Gpo's which sometimes are practical but sometimes they just end up being in the wrong spot, I would tend to go for suspended pendant type gpos on jack chain!

[Ashes]

Was speaking to my shed installer today just letting them know that they sent me an old version of the owner builder which caused my application to be rejected...:C

anyways..

they recommend that normally power conduit is run up next to the slab and up one of the ridges in the colorbond. Reasoning being that conduit in the slab weakens it. Same goes for mains water in. They recommend drain water be run out through the wall for the same reason as well..

does that sound right? If so, takes away the compexity of having to co-ordinate sparky, plumber and concreter

[rod1949]

... Reasoning being that conduit in the slab weakens it.

What a load of Cocky poo.

[silentC]

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.

:)

[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. :rolleyes::D:D

[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)

[patty]

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?

Get a Lic Spark in and he will do a Max Demand Calculation for the installation and install a mains cable from your existing meterbox on its own circuit to the shed the the size of the cable installed depends on many things 2 being are

1/ Max Demand of the Install ( the current drag your shed will use)
2/ The distance the shed is from the Meterbox to compensate for Volt drop)

As you can see by throwing in a conduit for the spark you might think you are doing him a favour but if you throw something in to small and the cble does not fit then what was the point of the exercise!!!<!-- / message -->

[Ashes]

Thanks guys. I will be talking to a licenced sparky near my house that has been recommended to me by a mate in the building trade. At least I should get a fair/honest quote this way.

Outcome should be that we run the required amount of conduit up through the slab into the right spot as well as some advice on best how to do the cable run from the house to the shed. Once I know where for sure we'll run the mains cable I'll get the ditch witch organised and make a mess of the back dust bowl/lawn and garden beds!!