UFH Pipe circuits and Ground beams

[Selexus]

51 minutes ago, Nickfromwales said:

Ok, so we’ve covered that your SE is on crack, but at least your floor won’t suffer the same way. We can set this lunacy aside now I guess. But I just like to say, after seeing the 100mm substructure, (expletive deleted) me down!!! 😳. Space x has a new home for next launch lol. 
 

Right. Back to UFH. 

Just go on top as going under and then dropping a Titanic amount of steel on top of the pipe is fraught with danger. If the pipe gets damaged you’d have to lift it all out, replace the pipe run, and go again. And repeat.

 

 On top it is! The partner will be happy to hear that 😆😉

Edited August 3 by Selexus

[Selexus]

1 hour ago, saveasteading said:

Green raft insulation. Is that Greenguard?  I wasn't aware of this bug just looked it up.

Makes sense to have extra strong insulation when under such heavy load as must be being designed for.

180mm of this appears to cost £48/m2.

 

I wonder if your SE has made the slab thick just to match the beam, and to spread the beam load wider over the insulation.

 

My stingy take on this is to have no insulation under this industrial floor and add extra elsewhere. Ground isn't a bad insulater anyway.

 

I'd love to see the calc's for this slab  as there is something I'm not grasping. OR the SE isn't great on value.... most aren't... only me and @Gus Potter.

 

 

Its Sopera XPS. Interesting stuff to work with.

I've bought a hot knife gun and have routed all the first fix pipe and conduit into the top of the insulation.

 

 

Edited August 3 by Selexus

[Nickfromwales]

I’m hesitant to ask, but did you go for a hot return to combat long runs to taps and to alleviate waiting for hot water to arrive? 

 

Good levels of planning though, as running 1st fix in the floors makes life a boatload easier downstream. 

[Selexus]

 

2 hours ago, Nickfromwales said:

I’m hesitant to ask, but did you go for a hot return to combat long runs to taps and to alleviate waiting for hot water to arrive? 

Oh yes. 

[Gone West]

Have you capped the ends of all the pipes and ducts?

[Selexus]

12 minutes ago, Gone West said:

Have you capped the ends of all the pipes and ducts?

Not yet, but it's a good shout.

Don't want a bit of rogue concrete blocking a water pipe and giving issues later....

[Gus Potter]

On 03/08/2025 at 13:50, Selexus said:

I'm with you Steve. I challenged our SE about the 250mm slab and he said his calculation fell apart at anything less than 250mm.

I design stuff like this as an SE. Sometimes it works out that a thick slab is the most economic. Sometimes it's just more buildable to keep an even slab thickness as you avoid funny rebar, shutering and so on. Labour and shuttering is expensive so you have to balance that by just making the lsab the same thickness. 

 

Just ask your SE why they think this is the most economic solution and why. They should be able to tell you. They may also give you some extra tips if you offer to pay a little more, chip in for the staff Xmas fund they will often refuse.  

 

The builder gets a drawing with the slab and rebar. A good SE will make this buildable and easy to understand, a key requirement. 

 

What you don't see is that in the SE office a huge amount of thought often goes into this. 

 

A raft slab is a complex animal and it takes a lot of time to learn how to design them well and buildable.

 

For all when I design raft slabs for the self build market I add some notes on my drawings like this: The last bit of paragraph one explains why I'm asking the builder to do what I want and the reason for doing it. If you don't let the concrete harden then it won't bond to the rebar properly. Let the concrete harden, then dry it out so the shrinkage loads are transfered to the rebar. 

 

 

 

[Nickfromwales]

On 03/08/2025 at 19:40, Selexus said:

 

Oh yes. 

Where are they installed?

[Selexus]

11 hours ago, Nickfromwales said:

Where are they installed?

 

Here. Left pipe is the hot return (from the local ensuite hot manifold) middle is the hot feed (now run in) and right is cold feed. All 20mm Pex-al-pex.

This ensures hot circulation at the main manifold (center of the house) and therefore short runs from there to each en-suite manifold.

 

[Selexus]

13 hours ago, Gus Potter said:

I design stuff like this as an SE. Sometimes it works out that a thick slab is the most economic. Sometimes it's just more buildable to keep an even slab thickness as you avoid funny rebar, shutering and so on. Labour and shuttering is expensive so you have to balance that by just making the lsab the same thickness. 

 

Just ask your SE why they think this is the most economic solution and why. They should be able to tell you. They may also give you some extra tips if you offer to pay a little more, chip in for the staff Xmas fund they will often refuse.  

 

The builder gets a drawing with the slab and rebar. A good SE will make this buildable and easy to understand, a key requirement. 

 

What you don't see is that in the SE office a huge amount of thought often goes into this. 

 

A raft slab is a complex animal and it takes a lot of time to learn how to design them well and buildable.

 

For all when I design raft slabs for the self build market I add some notes on my drawings like this: The last bit of paragraph one explains why I'm asking the builder to do what I want and the reason for doing it. If you don't let the concrete harden then it won't bond to the rebar properly. Let the concrete harden, then dry it out so the shrinkage loads are transfered to the rebar. 

 

 

 

 

Thanks Gus. I did have a chat with him and his explanations made good sense, although on the risk averse side

His reasoning was very similar to what you have pointed out.

Ease of build (we have a fixed flat base - existing concrete slab) and so incorporating all elements into the raft, and making it capable of surviving differential movement (like that's going to happen 🙄) of this existing concrete, is how we ended up with the 250 slab with integral ground beams. He certainly has put the hrs in thinking about how to design AND how i am going to build it, so fair play to him.

[Nickfromwales]

5 hours ago, Selexus said:

 

Thanks Gus. I did have a chat with him and his explanations made good sense, although on the risk averse side

His reasoning was very similar to what you have pointed out.

Ease of build (we have a fixed flat base - existing concrete slab) and so incorporating all elements into the raft, and making it capable of surviving differential movement (like that's going to happen 🙄) of this existing concrete, is how we ended up with the 250 slab with integral ground beams. He certainly has put the hrs in thinking about how to design AND how i am going to build it, so fair play to him.

So, in summary, it's too late to add a basement is what you're saying yes? lol.

[Selexus]

Don't put ideas in my head. 😆

[Nickfromwales]

22 minutes ago, Selexus said:

Don't put ideas in my head. 😆

[Gus Potter]

On 06/08/2025 at 12:43, Selexus said:

I did have a chat with him and his explanations made good sense, although on the risk averse side

Ok that's a great start.. good to see SE's explaining and reasoning out to Clients what they have thought about and why they are designing in a certain way and engaging with you. 

 

In terms of risk.. for all it's important to discuss with your SE this risk element and be up front about it. Some self builders are well funded and don't need to satisfy say the bank and are willing to take on more risk.

 

To add a bit of context. The thing you won't get an SE to compromise on is safety (not fall down) but there is scope when it comes to potential movement / shrinkage that could say crack floor finishes. The Eurocodes have an element of flexibility here where as the British Standards can be more prescriptive. I could agree with you what level of risk you want to take in terms of movement, provide the movement is not too large such that it impacts on the structural safety design. If you said to me.. hey Gus I don't care if my building sways to the side by 150mm I would then say to you.. now all the loads are off centre and this will add unwanted forces to the structural frame which makes it unsafe. 

 

The warranty providers (NHBC / ProteK) may not be so "flexible" when negotiating movement / settlement say.

 

On 06/08/2025 at 12:43, Selexus said:

He certainly has put the hrs in thinking about how to design AND how i am going to build it, so fair play to him.

Then in that case you have probaly got value for money. Just say your SE charged you an extra 5.0k! All he has to do is save you one week of work for 4 experienced operatives, add in some plant cost and the face is washed. Yes your slab on the face of it is thicker but it is flat, looks buildable and the drawings are probably easy to read which will avoid error on site. 

 

To finish. Go back to your SE and ask what the movement joints need to do. Is there some shear transfer. Are you going to have a tiled floor all over, you probably want to keep that level so you want to avoid on slab settling differentially. Once you get a handle on that then there are loads of joint options.

 

All the best.

[Selexus]

So... Had the conversation with my SE and after some discussion we settled on a standard cut control joint at these locations. The dowel joint was mainly specified to potentially placate the over zealous requirements of warranty providers that the SE has recently come up against in recent jobs. The SE has no issue with standard cut joints as there is minimal potential of differential settlement. He mentioned that contraction was the major concern, and if was ok with the cut joint opening up slightly over time, then he had no major concerns.

We have agreed to present a united front (from a risk and technical perspective) to said provider if they question the use of control joints, rather than dowelled joints.

The more I talk to him, the better I feel about this work.