Advice required please, Multi floor level and underfloor heating...

[DougT]

Hi,

i am new to this forum but after some advice if possible please. I am building a new extension and as part of the work i am knocking through between the new extension and an existing room. Ideally i would like Underfloor heating throughout. My plan for the new extension was pipe connected to 100mm insulation on top of concrete sub base - with a 75mm sand and cement screed on top.

However - because i am knocking through i have another floor level to consider as well (the existing floor). On ripping up the existing floor (wooden floor boards) - i discovered that the existing room is made up of two levels as well (see pics) - with one level approx 50mm lower than the other. Both are of concrete construction and neither appear to have any insulation. So - originally i was planning on doing the whole existing room with low profile UFH boards, with a ditra uncoupling matt on top followed by tiles....now i am unsure what options i have.....i dont want to dig up the existing floor....

Any advice really appreciated please - as at the moment i am very unsure on what real options i have....(and having 3 different floor bases in one room worries me in terms of different expansion rates etc....)

Thanks.

(photos of existing room only but can provide more if it helps)

 

[Dan]

I'm surprised this hasn't got more traction!

So, what's stopping you screeding over the lot now? What height do you have?

 

[J Sid]

Get all floors the same level with insulation boards, 50mm board on low area the over the lot with a low profile wet ufh kit

 

[Bopster]

As above, I did this in my own house.
Low profile ufh is a solfex system, been Down 5 years without a single glitch and Simple to install

 

[J Sid]

Right prep and installation and it'll last and work very well

 

[Old Mod]

Was half way thro writing exactly the same as @JulianSidney above, but was called away. 😊
I would add, wherever there is a break between different floors, insert expansion joint (this also entails splitting any matting on the same line, do not bridge the joints), even if it’s a 5mm Silicon joint, and with a heated floor there should be no area bigger that 40m2 without one.
What’s total area of intended finished floor?
That will deal with your 3 different substrates, and should alleviate your fears of 3 different expansion rates.
There will be different rules for the new screed, if pipework is laid in screed.

 

[Old Mod]

Avoid wet ufh in polystyrene boards with aluminium foil on top, seen many failures.