Under slab services

[Gibdog]

Hello BuildHubbers,

 

First post for me after months of learning all I can from others on here  We're an MBC passive house build in Stratford on Avon.

 

We need to send the service layout for under the slab connections- can anyone help/comment on the below? Or can anyone share their layouts to give me some ideas?!

 

1. Do all external lights/blinds/Security systems have to be wired directly from inside to out i.e. go through the airtight layer etc, or can you run a duct back under the slab to allow for all external electrics (between TF and timber/brick cladding)? 

 

2. Has anyone had virgin media fitted?  Can this come in under the slab too? At what point do Virgin themselves get involved?

 

3. Water: the mains water will come in under the slab. If we want an external tap, do we need to allow for another under slab pipe back to the exterior?

 

If there's a comprehensive thread on this subject, feel free to send me that way -  feel like I've looked but can't find full answers. Many thanks.

[twice round the block]

Under "foundation" sub section

conduits and services

[Gus Potter]

1 hour ago, Gibdog said:

We need to send the service layout for under the slab connections- can anyone help/comment on the below?

No because you have not provided any drawings!

 

Fesse up and share your drawings. Folk will then chip in and in return we may also learn a bit from you.

 

Them's the rule of the game!

 

[saveasteading]

1 hour ago, Gibdog said:

another under slab pipe back to the exterior?

No. It can spur off before it goes under the house. Take the chance to put stopcocks in all directions.

[deancatherine09]

So here's what we did;

 

1) We specified a separate return duct so all the outside lights and plug sockets go out of the building under the slab, then get routed behind the exterior cladding in the service cavity.

2) We have a specific duct in for the data and CCTV camera wires

3) We have two outside taps, one is teed off before the water pipe enters the house but the other one we ended up drilling through the house from the kitchen as it made sense given the location. We did all the airtightness taping etc and insulated the pipe.

 

You don't want to mix data and power cables in the same duct so map out what you want coming in and out, and go from there. MBC didn't charge us extra for the additional conduits we wanted but we did supply the pipe.

 

[FarmerN]

If you have a plant room or simmilar put at least one spare duct in to future proof for things you have forgotten or not even heard of yet.

[TerryE]

Another happy MBC owner here.  We put some extra 11 cm pipe runs down from the plant cupboard under the slab and out beyond the peripheral path .  We ran various services through these using various flex sleeving covers. These proved great during initial build, but were flawed for future additions -- basically after 2 years of external ground-works and landscaping the external covered pipe end got lost / buried too deep / covered by paving etc.  

 

We had a rule that no trades were allowed to breach the twin-wall, so we did all the through ducts / conduits then once the sparky etc had done using them we foam filled and silicon-sealed them all before the pressure test.  I only wish we'd put some extra through pipes "just in case" as well.  There are no air leaks and tiny U-value hits doing this to it;s a damn site easier drilling one of these out if you need to add extra services later than trying to add a new airtight through duct once the building has been boarded out and plastered / outer skin complete.

 

I ran power and Gb enet to a small shed close the house and added a PoE switch here so that all of the external cameras etc. could be cabled to this shed.

 

Edited December 20, 2024 by TerryE

[Gibdog]

Thank you all so much for your replies - I went offline over Christmas so apologies for not replying. 

 

I think this is how people tend to reply...!:

 

On 18/12/2024 at 23:08, Gus Potter said:

No because you have not provided any drawings!

 

Fesse up and share your drawings. Folk will then chip in and in return we may also learn a bit from you.

 

Them's the rule of the game!

 

 

Gotcha - didn't know that was a rule! Attached here (format OK?!) 

 

 

On 18/12/2024 at 23:12, saveasteading said:

No. It can spur off before it goes under the house. Take the chance to put stopcocks in all directions.

Ideally it would be on the garden (north) side - but the mains comes in at the front (south side) - would you then pipe it externally?! 

 

On 20/12/2024 at 12:52, deancatherine09 said:

So here's what we did;

 

1) We specified a separate return duct so all the outside lights and plug sockets go out of the building under the slab, then get routed behind the exterior cladding in the service cavity.

2) We have a specific duct in for the data and CCTV camera wires

3) We have two outside taps, one is teed off before the water pipe enters the house but the other one we ended up drilling through the house from the kitchen as it made sense given the location. We did all the airtightness taping etc and insulated the pipe.

 

You don't want to mix data and power cables in the same duct so map out what you want coming in and out, and go from there. MBC didn't charge us extra for the additional conduits we wanted but we did supply the pipe.

 

Ooo this is great thank you - 

1) This is what I was hoping to do but did you not have an issue with BC here? I've read that you can't run services out there?!

2) Thank you. Really silly question - but hopefully this is a safe place(!) - when you say "duct" - are there different types you're meant to spec?!

3)Thanks - not sure I like the sound of drilling through! As above, perhaps I tee it off before it enters the house then pipe it external round the side...

 

I don't suppose you'd be up for sharing your under slab plans would you? I'm a very visual person so seeing how it's done on other projects (especially an MBC one) would be really useful!

 

On 20/12/2024 at 16:36, TerryE said:

Another happy MBC owner here.  We put some extra 11 cm pipe runs down from the plant cupboard under the slab and out beyond the peripheral path .  We ran various services through these using various flex sleeving covers. These proved great during initial build, but were flawed for future additions -- basically after 2 years of external ground-works and landscaping the external covered pipe end got lost / buried too deep / covered by paving etc.  

 

We had a rule that no trades were allowed to breach the twin-wall, so we did all the through ducts / conduits then once the sparky etc had done using them we foam filled and silicon-sealed them all before the pressure test.  I only wish we'd put some extra through pipes "just in case" as well.  There are no air leaks and tiny U-value hits doing this to it;s a damn site easier drilling one of these out if you need to add extra services later than trying to add a new airtight through duct once the building has been boarded out and plastered / outer skin complete.

 

I ran power and Gb enet to a small shed close the house and added a PoE switch here so that all of the external cameras etc. could be cabled to this shed.

 

Thank you too!  Great idea to have something running to shed, even if we don't use it straight away. As above - I wonder if you'd be up for sharing the doc you sent to MBC with under slab details?

[Gus Potter]

On 02/01/2025 at 14:12, Gibdog said:

Gotcha - didn't know that was a rule! Attached here (format OK?!) 

Well done pletty to mull over here!

 

Will try and respond once have had time to digest.

 

[TerryE]

On 02/01/2025 at 14:12, Gibdog said:

I wonder if you'd be up for sharing the doc you sent to MBC with under slab details?

 

I'd have to dig through 10 year-old files for this sorry.  Our plant area all fits in a 80 × 150 cm cupboard that is along one side of our downstairs loo.  The UFH pipes and the two pipes come up into this.  I use the 110 mm foul-water push fit  OSMA pipe for these -- the same as my FW runs running under the slab in the crushed MOT 3 layers.  (You need slow bends to turn up into the slab to make it easier to pull wiring and pipes through them.)   As far as the MBC crew was concerned these were just prepped and laid the same as the two FW runs that lead to my 2 internal FW risers.