UFH + Existing Property

[irfy11]

Hi all

Hope the experts can help as more people I talk to the more I am getting confused. I am getting some work done and will be UFH in the extension however I would also like it in my existing property as it will be open plan. The existing property is built on a raft foundation and was built in 1990. As far as we are aware there is no insulation. There are two options I have been told I have. An overlay board which will decrease my height of ceiling which is already quite low. Or I can get grooves milled into the existing concrete. The main question I have is that regardless of both I will be losing heat below but which is the two of the lesser evils as such.

*Is there much difference between heat loss between an overlay board or milling?
*Is losing the height by using an overlay board better for heat.

My builder has said we cannot dig down on Raft Foundation as this is what is supporting the house as I was looking into options of digging down 150mm. Put down 100m insulation and then 50mm screed on top. Is this the case and you cannot take out 150mm from concrete of Raft Foundation.

Thank you for any advice you can give.

 

[Mr Chibs]

Not heard of the 'milling' before, but I imagine the mess and cost to be high, not sure you want to much around with the raft.
Also even if you rout the UFH pipes into the slab, there is no insulation, so the heat will be taken up by the slab and the ground will leach some of the heat.

I don't see you have many options other than to use an overlay system, although the insulation will be small, there will be some.

What floor finish are you having? and how height much can you afford to lose off the room?

 

[irfy11]

Thank you Mr Chibs. Been quoted 1k for milling 44m2. Company will come out no dust and mill it out using a dedicated machine.

I will be having carpet in one of the lounges where it will be milled and tile in the hallway-kitchen. Dont want to lose height as current height is 2.3m.

It is a toss up between losing height i.e 20-25mm and using overlay and how much this will help with insulation if any.

Or mill into Slab and have a % of heat loss but with no loss of height in room.

Looked at Robbens overlay system which is German and Nu Heat Lo Pro. All they do is put pipes in a Mat. The Mats dont have any insulation property as far as I am aware.

 

[Madrab]

Milling/channeling, is a retrofit into an existing slab, problem with that is, if it's understood there is no insulation below the slab then that will be highly inefficient and definitely not recommended.

Overlay board - 18>22mm - made of high density polystyrene with a foil heat spreader layer on top. 90% the heat travels upwards and if height allows add a further layer of insulation beneath to increase that.

Minimal loss in overall ceiling height. It is more expensive per M2 to install than screed but there are several benefits to the system. I have installed both and find the overlay system a great retrofit.

 

[Mr Chibs]

Had a watch online of milling the floor, its impressive, but for me, there is still a lack of insulation, and a good proportion of heat will dissipate through the ground...

Also, not sure carpet is the most efficient covering for UFH, usually it's tile/stone.

Sure you will get an expert to give you more info.

Perhaps as a guide you should see what wall insulation figures are for no insulation vs, 25mm foam, as this may give an idea of wether you are talking 5% or 50%.

 

[Madrab]

As an addition - I have used overlay boards (Wunda - EPS400@ 16mm) with a 6mm backer board ( No more Ply) and then a low tog underlay (Duralay King designed for UFH) and carpet (Low tog <2 Cormer) in one room it works superbly well and the rest of the downstairs in engineered wood.

 

[irfy11]

Thanks Madrab. So a total increase of 22mm.

 

[Madrab]

The total increase for the carpeted area was 20mm for the overlay panels and 6mm for the backerboard. The wood lays directly on top of the panel, so would the tiles. So just 20mm for the panels. Given you are looking to lay it directly onto an uninsulated slab an additional 5mm thermal barrier may be of benefit, even with that you're really not taking a lot away from the overall ceiling height. 30mm is not a lot IMO > 2.27m as against 2.3m
The beauty of the system is that it is direct heating rather than heating up a thermal mass and maintaining that as with a conventional slab.

I.E. you use and treat it as you would a normal CH system, switch on the CH as you would radiators and the UFH heats the floor covering quickly and directly. That and you still run it @ 45-50deg sys temp so gain the benefit of a conventional slab UFH lower running costs.