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UFH and new stud walls

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This hopefully will be a straight forward answer to you guys in the know... hopefully!


I have an old stone build (stone and rubble) farm house, with concrete floors.  We are planning on UFH with air source.  We're planning on 100mmpir on the concrete, membrane, then pipes and screed, raising all door heights to take account of the new 150mm (100mm pir and 50mm screed) higher floor level.  But, we plan to stud out some of the externally facing walls - building an internal stud frame and insulating between the studs (100mm pir), before new plasterboard and then skimmed.


Question #1  is...

do I stud first, to the plasterboard stage, then insulate the floor, pipe and screed, or...

do I insulate to the existing walls, pipe and screed, and then erect the stud work on top of the screeded floor, remembering to leave the pipe work away from the edges to take account of the new internal walls? 


I'm guessing stud first, but I'm no expert!  Any advice appreciated.


Question #2 is...

All but one floor is concrete - the only other ground level floor is a suspended timber floor, with joists.  Don't ask me why they did all but one... I have no clue!

We want a consistent floor level throughout the ground floor, so will need to bring the suspended floor up to the same height.  We plan on again using 100mm pir, but that leaves 50mm (which would have been screeded in the remainder of the property).


If I go with a wooden board clip-in system for this one room, how best to make up the 50mm??

If the board system where the pipes are placed is 20mm say, and the whole floor is then covered with 9mm ply, (20-9 = 29) that leaves me with 21mm to pad out to get me to the overall uniform level of 50mm? 


Do I go for 120mm pir, or

Do I go for a 20mm board below the PIR to make up the difference?? 


Thanks in advance!



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Q2 first as that's easiest 🙂 Fit more PIR. Always fit more insulation if you can 🙂


Q1. My approach would be as follows:

  • Membrane bringing it up the walls by 250mm
  • 100mm PIR
  • Around the edges fit an extra 50mm of PIR the width of the studs you propose to fit. (for belt and braces approach, seal the joints between the PIR)
  • Lay pipe and screed in the resulting "paddling pool"

You should now have a screeded floor with an edge of PIR showing, the width of your proposed studs

  • Now fit your stud work atop the PIR edge, fit the PIR between and plasterboard the walls.
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  • 2 months later...

Just be super careful with stone buildings. They function in a completely different way to standard buildings.

For your external walls, do not put stud and PIR in there. One thing to remember with stone buildings is they need to be vapour permeable.

If the walls cannot breathe, they will cause damp and mould issues behind. Because stone buildings didnt have proper foundations, damp will get into the walls (especially if internal floors are concrete)

Use something like wood fibre insulation instead, it will allow the heat to get to the stone and prevent a mushrooming in the gap


When I started taking off that stuff from my place, the first floor started to come down as it had rotted the timbers.

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On 07/05/2024 at 19:27, damocoleman said:

For your external walls, do not put stud and PIR in there. One thing to remember with stone buildings is they need to be vapour permeable.

I'd avoid PIR too, for the same reason. I'd either be looking to use hempcrete, or hemp / wood fibre insulation batts.

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I'm a big fan of plant based materials. If I could marry dense pack cellulose I would. (Don't tell my wife!)


However they're not the be all and end all nor solution to all problems. 


Moisture is however, the root and cause of all issues and if you can't logically deal with it then trouble is down the line, espically in old buildings. 


At the moment you have a concrete floor that is quite vapour impermeable and stone and lime walls that takes up the slack by being somewhat vapour open. If you have any localised high water tables then moisture that would have originally dried up through a clay floor now is pushed up through the walls. As they're somewhat warm on the inner surface and as they're not sealed with an impermeable layer the moisture can dry harmlessly to the inside. 


Before you think of internally insulating these walls and making them permanently cold you must first ensure that they have the least moisture pressure possible by lowering the localised water table. Do this by installing a french drain outside the house to well below the level of the floor, ensure all gutters and drains are clear and working and external pointing and render is A1. 








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