eandg

Servicing and foundations/passive slab

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Hi, no doubt a very basic question here. We have a serviced plot; how do we bring the services in above the slab? 

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Best bet is to have all the pipes/ducts run under the sub-base and then come up vertically through the insulation and slab.  It needs very careful laying out to get all the services in exactly the right location, plus ducts need to be run with gentle bends, so things like MDPE water pipe can be pulled in OK (or in our case a fat three core power cable).

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2 minutes ago, JSHarris said:

Best bet is to have all the pipes/ducts run under the sub-base and then come up vertically through the insulation and slab.  It needs very careful laying out to get all the services in exactly the right location, plus ducts need to be run with gentle bends, so things like MDPE water pipe can be pulled in OK (or in our case a fat three core power cable).

And through to every room they're needed? Would you expect your slab contractor to specify what's required or do you need to specify it for them?

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In our build soils/wastes went under the slab.  UFH pipes in the slab.  A couple of ducts for kitchen island and floor sockets and everything coming in through ducts under the slab and up into the plant room. All (including water) were then run around the house in service voids in walls/ceiling  starting from from the incoming points in the plant room.

 

Our ducts for the kitchen and recesses for floor sockets were too small...had to be hacked about.  Every single one of our soil pipes/wastes was in the wrong place. Plans  wrong, no one noticed architect had drawn the things wrong not corresponding to bathroom layouts so my wall hung w.c.’s would have been a good 8 inches out from the wall,  Slab had to be hacked out to realign it was very worrying due to UFH

 

We are single story so every bathroom was wrong.

 

The whole slab thing was utter hell.

Edited by lizzie

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AFAIK only for ground floor soil pipes. Water, electricity, phone etc are generally run round the house in service voids. 

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39 minutes ago, eandg said:

And through to every room they're needed? Would you expect your slab contractor to specify what's required or do you need to specify it for them?

 

Usually water, telephone, electricity just needs to enter in one and then the internal pipes, cables take over.

 

Drainage positions needs to be considered before the slab is poured.

 

On our build (we didn't have a single contractor) the internal drainage did seems to be a job of with it being a bit unclear as to who is responsible, luckily our brickie and plumber were pals so was not an issue.

 

If you have a slab contractor I would think it was their responsible, but  I would clarify.

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As a note of caution, you are not allowed to run power cables in the same duct as telecommunication cables.  Best to have a duct for each service that comes up through the slab.  As @lizzie has pointed out, it is your responsibility to get all these services coming up through the slab in the right places; as I mentioned above, accuracy in getting these spot on is critical and it's one of those key interface areas where you need to be certain that the people running the ducts and pipes in (often the ground works team) have got them all in exactly the right location.

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50 minutes ago, JSHarris said:

As a note of caution, you are not allowed to run power cables in the same duct as telecommunication cables.  Best to have a duct for each service that comes up through the slab.  As @lizzie has pointed out, it is your responsibility to get all these services coming up through the slab in the right places; as I mentioned above, accuracy in getting these spot on is critical and it's one of those key interface areas where you need to be certain that the people running the ducts and pipes in (often the ground works team) have got them all in exactly the right location.

 

Did you get any of these into contracts, or was it case of meticulous supervision by you, @JSHarris? This is presumably to something like +-5mm, perhaps 10mm.

 

A downside of achieving that would be to make change difficult wrt the plans linked to the contract, whilst not doing that means the risk falls on the self builder.

 

I think that I would look into dealing with this by putting the big ones into the slab eg soil pipe, whilst using some arrangement in the floor buildup for electricity distribution, combined with as little service void as possible. I do not have a mature scheme of this type for a new build, however.

 

Ferdinand

 

 

Edited by Ferdinand

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All down to supervision and cross-checking by me, I'm afraid.  I did put the exact location of everything coming up through the slab on the drawings that were part of the ground works contract, with allowable position tolerances, but the contractor thought I was crazy in stipulating such precise positions.  On his last day on site I insisted we get the total station out and accurately check the position of everything.  He grudgingly obliged, and I was happy things were OK, but the soil pipe ended up being mighty close to the inside face of the North wall, and caused me about a days work to chip around the slab and get enough clearance to move it maybe 20mm.  My fault, the tolerance on the position I put on the drawings (+/- 40mm) was too great, it should have been about +/- 20mm.  All positions were referenced to a fixed post, with a marker, at the corner of the plot.

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One of the reasons I am contemplating a "wet wall" --type of construction ==so there is a walk in service access( for slim folk ) down north side of house  where you want few windows .

from one end connected to service room 

a waste of space you may say --but any alterations in future can be done without destroying and internal finishes.

may not be possible --we will see 

Edited by scottishjohn

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Thanks for the responses. Any recommendations for contractors? 

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And can you do a passive slab when ground conditions are generally unfavourable (e.g. a couple of metres of made ground) or does reducing the amount of concrete poured reduce its stability?

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If you think you might be planning a future garage, summer house, home office, (hot tub?) etc then worth thinking about cable ducts to go out under the slab if your cu is in a plant room within the house. Ditto ducting if your planning hardwired CAT, CCTV etc to a remote building.

 

Similarly if you're planning an ASHP then ducts in for the pipework and power, insulated ducts in the case of the ASHP possibly or big enough to take pre insulated pipes.

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You need to talk to an engineer. We are having a passive slab & he wanted non made up ground, I am sure there are ways round it (presumably at a cost!), but you need to go with what they say. It would be worth contacting Hilliard Tanner in Ireland if your engineer isn't that familiar with this method of construction. 

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Thanks both. We are/were waiting to get a design sorted before contacting a structural engineer but will get onto it asap. 

 

The ducting/cabling is one I'll need to get my head round - are there any straightforward guides about? I watched a few videos of passive slabs last night and they looked to be completely without anything bar EPS and concrete!

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2 minutes ago, eandg said:

Thanks both. We are/were waiting to get a design sorted before contacting a structural engineer but will get onto it asap. 

 

The ducting/cabling is one I'll need to get my head round - are there any straightforward guides about? I watched a few videos of passive slabs last night and they looked to be completely without anything bar EPS and concrete!

 

Our passive slab was laid on a  bed of whacked down coarse stone:

5741978318605_Housebase-Copy.thumb.JPG.182ed4223419def89122bf1c53810cdb.JPG

 

You can just see the pipes and ducts coming up through this, they were all placed accurately in trenches underneath the sub-base.

 

Next the sub-base stone was blinded and levelled with grit, to form a dead level bed for the shaped EPS blocks and sheet:

 

5742a9d725edb_Housebasegoingdown2.thumb.JPG.2cb63fd645aa16f7221ee11a83c6b10b.JPG

 

You can see some pipe/cable ducts poking up at the back of this photo.

 

Once the foam blocks and sheet were all laid, a DPM was laid and sandwiched between the top foam sheet and the two underneath, the reinforcing steel was added and tied in and the UFH pipes were laid and tied to the steels:

 

 

5742a9e1b7acd_Housebasegoingdown3.thumb.JPG.a63fda24b89aa8a83265410681437f1e.JPG

 

The day after the photo above was taken the concrete was poured and trammelled roughly level, as shown in this photo:

 

5742a9e52e8b2_Housebasegoingdown4.thumb.JPG.c34a2fdab7c02c6aa53c109c606ba0f8.JPG

 

A couple of hours after the photo above was taken the slab was power floated smooth, leaving a finished floor that was flat and smooth enough to tile and floor to directly, with no need for screed or levelling compound.

 

 

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