Insulated Slab Question

[Iceverge]

3 hours ago, Shaun McD said:

I also have a specific request from the better half to ensure our ensuite shower has LOADS of water pressure. 

 

Get a definition of that in litres/minute. In writing preferably 😁. Use a measuring jug and a known shower and time it to see how much "loads" of water qualifies.  

 

We have 10l/min showers from 15mm feeds direct from the hot and cold manifold. We have a bored well so water pressure is what ever we want it. Normally 3-5 bar.  It is reduced to 3bar by the control block before the tank.

 

My wife with her super thick hair only uses the shower on half throttle via the thermostatic mixer. I got the same result from the one I installed for my parents despite their well pump being nearer to 2 bar. For comparison the electric Triton shower they have is only 3.3l/min. 

 

Beware that if you do opt for a 20l/min flow head it'll empty a 300l 48deg UVC in about 8 mins. 

 

You would need a tremendous amount of storage or a 50kW boiler to keep up with such a behemoth. 

 

For the services I did a 2*44mm service cavity for the first floor so could put the MVHR ducts there. 

 

In hindsight 20mm just for wires would have been fine as I was the one who would have been taping the plenums in the membrane for airtightness and could have done a robust job. 

 

 

 

 

 

 

 

 

 

 

 

 

[Shaun McD]

2 hours ago, Thorfun said:

if you have a warm roof (or warm loft) with the insulation between the rafters then your loft space will be within the heated and airtight envelope which will allow you to run services in the loft space easily and without worrying about heat loss in to an uninsulated void or penetrating the airtight layer.

 

No our airtight layer is at ceiling level, will be a cold roof. Pipe on top of joist will be encased in insulation (due to depth) but will be outside the airtight layer

 

2 hours ago, JackofAll said:

@TerryE @Nickfromwales not sure if how they lay the pipes in this clip is right but it sure does look easy. 

 

 

This is what I was thinking would be the norm for plumbing with an insulated slab, not that I have been involved in any

 

23 minutes ago, Iceverge said:

 

Get a definition of that in litres/minute. In writing preferably 😁. Use a measuring jug and a known shower and time it to see how much "loads" of water qualifies.  

 

We have 10l/min showers from 15mm feeds direct from the hot and cold manifold. We have a bored well so water pressure is what ever we want it. Normally 3-5 bar.  It is reduced to 3bar by the control block before the tank.

 

I will get the bucket out later and see what current one is at, gut feeling is it wont be 10l/min!

 

23 minutes ago, Iceverge said:

For the services I did a 2*44mm service cavity for the first floor so could put the MVHR ducts there. 

 

In hindsight 20mm just for wires would have been fine as I was the one who would have been taping the plenums in the membrane for airtightness and could have done a robust job. 

 

I think I will need 90mm pipes due to some of my run lengths. I guess though it may be simpler to run the pipes on joist, and have the plenum penetrate the airtight layer, as even a 100mm cavity will likely not be enough for the plenum anyways 

 

[JackofAll]

59 minutes ago, jack said:

 

As far as I can tell, most people on BuildHub who have an insulated raft have their UFH pipes zip-tied to the reinforcement mesh as shown in this video. It's certainly how mine was done.

@jack the hot/cold feeds  appeared to be in the same layer as the ufh pipes, thought that strange also the way they used the hot cutter definitely seems easier for hot/cold feeds rather that running ducting under the slab.

Edited February 27, 2023 by JackofAll

[jack]

10 minutes ago, JackofAll said:

@jack the hot/cold feeds  appeared to be in the same layer as the ufh pipes, thought that strange also the way they used the hot cutter definitely seems easier for hot/cold feeds rather that running ducting under the slab.

 

Ah right, I understood "pipes" as being UFH pipes.

 

The hot and cold water pipes are embedded within the insulation, not the slab. That said, the top of the pipes (or at least the coloured conduit they're run in) does seem to be in contact with the slab.

 

The pipework being in contact with the slab is going to make the cold water potentially quite warm when the UFH is on. Maybe that's fine (and perhaps preferable to having it being very cold, which might be the other alternative in Sweden where it looks like this house is being built).

[Thorfun]

44 minutes ago, Shaun McD said:

No our airtight layer is at ceiling level, will be a cold roof. Pipe on top of joist will be encased in insulation (due to depth) but will be outside the airtight layer

thought about changing that? for us i figured it'd be easier to not have to worry about light fittings penetrating the airtight layer if at ceiling level. also, it means that anything i store in the loft will be at house temperature rather than outside temperature! it just kind of made more sense to me.

[Shaun McD]

5 minutes ago, Thorfun said:

thought about changing that? for us i figured it'd be easier to not have to worry about light fittings penetrating the airtight layer if at ceiling level. also, it means that anything i store in the loft will be at house temperature rather than outside temperature! it just kind of made more sense to me.

 

Thought about it briefly yeah, my understanding was that it would cost us more to get the same level of insulation on the rafters as it would flat on the joists, and it would have additional costs like double battens. It would also increase the volume we would be heating. We plan to have only one area of pitched roof accessible for storage and dont think anything needing stored will be too important. If i was more DIY with the insulation then would likely be more keen on it

[JackofAll]

46 minutes ago, jack said:

 

Ah right, I understood "pipes" as being UFH pipes.

 

The hot and cold water pipes are embedded within the insulation, not the slab. That said, the top of the pipes (or at least the coloured conduit they're run in) does seem to be in contact with the slab.

 

The pipework being in contact with the slab is going to make the cold water potentially quite warm when the UFH is on. Maybe that's fine (and perhaps preferable to having it being very cold, which might be the other alternative in Sweden where it looks like this house is being built).

Apologies, should have specified which pipes.

[Iceverge]

1 hour ago, Shaun McD said:

100mm cavity will likely not be enough for the plenum anyways 

 

 

Correct.

 

I had to recess the membrane to fit them.

 

Just make sure one hole = one pipe.  Sub out the membrane where the ducts go through with a sheet of ply and use a 90mm hole saw to make a robust solution for sealing holes. 

 

Same story for wires. 

 

 

 

 

[Shaun McD]

2 minutes ago, Iceverge said:

 

Correct.

 

I had to recess the membrane to fit them.

 

Just make sure one hole = one pipe.  Sub out the membrane where the ducts go through with a sheet of ply and use a 90mm hole saw to make a robust solution for sealing holes. 

 

Same story for wires. 

 

 

Sounds good, never thought much on timing of this, i.e. will the plenum be in before membrane or after. Will need to confirm with TF company what the plan is

[Iceverge]

After would be easier. 

[Shaun McD]

20 minutes ago, Iceverge said:

After would be easier. 

 

Yeah, I need to understand their order of operations, ideally membrane on ceiling but wall cavity open for first fix would be ideal I think

[Iceverge]

You should have your airtightness test before the walls and ceilings boarded out. 

 

This will mean you can remedy any bad leaks. 

 

It normally gets a little worse for the final test as invariably someone will have made a few small holes and not patched them up. 

 

[TerryE]

@Shaun McD, As @jack says at 20,000 ft, our warm slabs used a broadly similar approach albeit with some difference because specs and BRed variations, e.g.  MBC wacks down the subbase in 5cm layers to guarantee compaction; EPS thickness is typically 30cm; the upstand section are factory pre-cut; the rebar is typically a lot heavier for 2 and 3-storey houses; and most UK BCOs would be unhappy about burying 25mm MDPE in the slab, even if rebated into the EPC. 

 

Here is our slab being poured, but we have a 2½ storey Larsen-strut TF proving the structure (hence the heavy load-bearing ring foundation) with a stone cladding for weather-proofing and  looks.

and as finished:

 

One of the other posters was questioning about pipe pressures, etc., so a couple of useful references from one of blog posts on plumbing design: ...  such reference works as this excellent intro into pipework calculations: John Heartfield, Water Flowing in Pipes I – The Theory  and useful sites like the Pipe Pressure Drop Online Calculator.  The first is worth a scan if you want to get a handle on some of the sizing issues.

Edited February 28, 2023 by TerryE

[Shaun McD]

Got my quote from Kore today and as if I wasn't conflicted enough already, the quote is not massively off what I would have been expecting the floor insulation + screed to cost alone. Site is not that uneven, so struggling to see how it will not work out cheaper doing an insulated slab.

Trying to put together a list of items that would need to decided up front if we go that route, please let me know if i'm missing any, or any you think I should consider/add;

• UFH layout and manifold positions
• DHW and DCW feeds (assuming I would cut into insulation as in the video in this thread)
• Incoming water feed from garage (We are in a region with not infrequent water outages, in current house we have a 1000l tank in garage which services all cold feeds except kitchen sink and downstairs toilet, and this system works well. Also allows us to have our pump in the garage so no noise concerns)
• Incoming mains water feed for kitchen sink and toilet.
• Trunk for incoming power from garage (meter box will be installed on detached garage wall). Thinking 50mm duct - red
• Trunk for incoming phone/internet from garage (again box will be on garage wall) - 50mm duct - red
• Service duct to garage (allows networking to/from garage, externals, gates etc.) - 50 duct - black
• Spare service duct to garage (future proofing for any expansion of PV etc. route cables to garage and have a path into house which can be sealed on both ends easily, and not have to drill into house) - 50mm duct - red
• Toilet wastes
• Sink/shower wastes - how are these normally handled? Do people leave in a dedicated 4 inch waste for each?

Anything I am missing? 

[TerryE]

We took our incoming power through from the meter box (in armored cable), up the service cavity and floor void to the distro box, so the up-and-over route is an option here.

 

It's a lot easier to pull stuff through 110mm than 50mm, especially if you turn up through the slab using a slow bend.

 

Also ASHP double insulated pipe runs to your potential ASHP location.  Even if you don't fit an ASHP on day one; it's a lot easier to future proof before pouring the slab than digging up after you are in.

[Shaun McD]

9 hours ago, TerryE said:

We took our incoming power through from the meter box (in armored cable), up the service cavity and floor void to the distro box, so the up-and-over route is an option here.

 

It's a lot easier to pull stuff through 110mm than 50mm, especially if you turn up through the slab using a slow bend.

 

Also ASHP double insulated pipe runs to your potential ASHP location.  Even if you don't fit an ASHP on day one; it's a lot easier to future proof before pouring the slab than digging up after you are in.

 

Thanks @TerryE good note on 110mm v 50mm, makes sense.

We are planning on ASHP so thanks for that call out too!