UFH difference in insulation height between kitchen and hall

[mattwaddy]

So the finished insulation floor height in my kitchen is about 12mm lower than the hallway due to an issue with the concrete depth being off to what was specified. The wet ufh loops are going to all rooms downstairs and for the kitchen loop it will need to cross this 12mm height difference, the kitchen will end up with a slightly deeper flow screed level as a result, but I just want to check that this will still work ok? i.e. the pipes will end up with flow screed supporting under the transition point to the room. I'm hoping it's going to be ok, best laid plans and all that

 

[emerylloyd]

If the flow screed is being poured for ground floor completely, or at least the kitchen and hall together I can't see any issues.

For me I'd say a join at the kitchen/hall meeting point may possibly cause an issue with any settlement but a smarter guy than I should answer that!

 

[robinbanks]

It will be fine

What depth of insulation have you put down, btw? Have you made sure there is a border of insulation all the way round the edge of where the screed will be poured? Have you made sure to leave ducts for services for things like kitchen islands and the manifold supply?

 

[mattwaddy]

It will be fine

What depth of insulation have you put down, btw? Have you made sure there is a border of insulation all the way round the edge of where the screed will be poured? Have you made sure to leave ducts for services for things like kitchen islands and the manifold supply?

150mm pir in the kitchen, complete dig out. and 225mm in the other rooms which used existing concrete slab below suspended floor. We've got eps70 25mm upstands all around walls internal and external.

 

[robinbanks]

eps70 25mm upstands

Oof, all that really good thickness of PIR and then such a skinny bead of poorer performing insulation on the colder parts of the structure.. If you've got time, I'd consider changing it out for 50mm PIR

 

[mattwaddy]

Oof, all that really good thickness of PIR and then such a skinny bead of poorer performing insulation on the colder parts of the structure.. If you've got time, I'd consider changing it out for 50mm PIR

Building Inspector suggested not to use pir for the upstand. I had originally planned to use it

 

[robinbanks]

Did they give a reason?

 

[mattwaddy]

Did they give a reason?

Density as I was planning to skip an expansion strip, instead just having an upstand

 

[robinbanks]

"Because density"

What does that even mean? What's the logic behind isolating the slab from the ground using a good amount of insulation, and then using insulation that's 15 times worse to isolate the same slab from a part of the structure that is directly connected to the ground you spent a huge amount of money and effort isolating the slab from?

 

[Mr Chibs]

I have both on my UFH, insulated upstand and foam compression layer.

 

[mattwaddy]

I have both on my UFH, insulated upstand and foam compression layer.

What thickness of upstand? and was it pir?

 

[mattwaddy]

"Because density"

What does that even mean? What's the logic behind isolating the slab from the ground using a good amount of insulation, and then using insulation that's 15 times worse to isolate the same slab from a part of the structure that is directly connected to the ground you spent a huge amount of money and effort isolating the slab from?

PIR isn't recommended due to it been so dense as it doesn't have sufficient flexibility for slab expansion (apparently). The upstand I thought was only to prevent cold bridging with the walls, there isn't the same contact surface to be a major issue, or perhaps I'm missing something? I've not seen anyone use or recommend 50mm pir before when scouring forums on upstands. I'm a novice though so happy to be enlightened on the subject.

 

[Mr Chibs]

I used 50mm PIR for cold bridging, then a foam compression roll for expansion, think its around 12-15mm thick.
The floor won't move that much.

 

[Mr Chibs]

Use polystyrene for your upstand if you are worried about it, as this compresses more than PIR

 

[robinbanks]

it doesn't have sufficient flexibility for slab expansion

anhydrite screeds expand at a rate of 0.012mm per meter, per degree. In essence this means if your house is 10 metres wide, and your screed is laid and dries at 15 degrees C, when you run it at 27 degrees C, the floor will expand by 0.7mm on each side of the room.

One of three possible things could happen when the floor expands

* The walls and PIR are so strong, the screed will bow up in the middle by 73.5mm
* The screed and the PIR are so strong, the walls will be shoved outwards along the foundations by 0.7mm
* The PIR, which won't be hard up against the wall or the screed, will compress by 0.7mm

If you're in any doubt as to which of these will occur, just press on the surface of a PIR board with your fingers next time you have one to hand