Overlay UFH height difference

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Getting an extension done to the house starting next month, where we're taking the current kitchen which is about 4*5m and extending it to 7*6m.

In the design the architect has specified underfloor heating which we don't have currently in the house, it's currently got 1 radiator. Ideally we'd like to stick to that plan and have UFH in the room, the rooms quite large and doesn't have a lot of wall space with a lot being kitchen cupboards and windows.

Currently the flooring between the hallway and the soon to be extended kitchen are completely level, and the builder is proposing to leave the concrete slab for the current kitchen as it is, and buiding all of the extended area to the same height. They'd then put down a thin overlay UFH. Then LVT on top of that to match the hallway, but there'll be around an 18mm height difference and a threshold to make it neat. My concern is that 18mm is a large change in height and people could trip etc.

Is that a sensible approach, or what would be better?
 

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Getting an extension done to the house starting next month, where we're taking the current kitchen which is about 4*5m and extending it to 7*6m.

In the design the architect has specified underfloor heating which we don't have currently in the house, it's currently got 1 radiator. Ideally we'd like to stick to that plan and have UFH in the room, the rooms quite large and doesn't have a lot of wall space with a lot being kitchen cupboards and windows.

Currently the flooring between the hallway and the soon to be extended kitchen are completely level, and the builder is proposing to leave the concrete slab for the current kitchen as it is, and buiding all of the extended area to the same height. They'd then put down a thin overlay UFH. Then LVT on top of that to match the hallway, but there'll be around an 18mm height difference and a threshold to make it neat. My concern is that 18mm is a large change in height and people could trip etc.

Is that a sensible approach, or what would be better?
I would be very wary of using an overlay UFH, over an existing floor if it is uninsulated

UFH is fantastic if it is a piped system and heated by heat pump or gas boiler and the floor is a new floor with 100mm of celetex with in screed pipes....because the screed is fully insulated all round and acts as a heat sink. If you use underfloor heating on an existing floor, the heat will be fighting cold concrete all the time.

has anybody done heat loss calcs as a mat might struggle to provide enough heat to work as the primary heat source

in regards to 18mm height difference -Its probably just about ok as long as you have a threshold the width of the door lining -say 135mm
 
UFH is fantastic if it is a piped system and heated by heat pump or gas boiler and the floor is a new floor with 100mm of celetex with in screed pipes....because the screed is fully insulated all round and acts as a heat sink. If you use underfloor heating on an existing floor, the heat will be fighting cold concrete all the time.
Whilst I certainly agree that an insulated slab with a min 100mm insulation underneath with an in pipe screed on top, is certainly the traditional way to do UFH but an overlay system is specifically designed to retrofit UFH onto the top of existing slabs with minimal heat loss downwards.

The design of an overlay system though is that it uses 22mm foil topped insulated EPS boards, they minimise downwards heat transfer into the slab and the foil top acts as a spreader plate allowing most of the heat to be transferred into the floor covering. That being said we have found it prudent to add an extra insulating layer between the base of the EPS and the concrete slab. We have had great success with a layer of 10mm EPS then the overlay. We have also used the existing P5 board as a bed to lay the EPS on and the wood acts as a thermal barrier.

OP, Please don't get your builder to fit the UFH, please ensure they have a plumbing/heating engineer in to do the design and the work. 18mm overlay sounds like they want to use a 12mm PEX, so will need narrow pipe spacing. I do think they need to design this out properly though and just throwing 18mm EPS straight down might not be the best idea. Lowering the existing flooring and then look at a proper overlay setup for the new floor may be advisable.
 
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I will say the builder is working with a plumber for the UFH, and it was said that they'd use the product they're suggesting before. I'm unsure how insulated the flooring below the concrete is, but it's not cold at present.

My main concern really is the height change rather than it being a insulation issue.
 

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