Minimum depth

[ts276]

I am considering retrofitting UFW in my kitchen, which is around 5 square metres, uninsulated solid concrete floor (not suspended). If I remove the existing sand and cement screed I should have about 6cm depth to work with.  Any deeper would mean cutting into the underlying concrete slab or raising the floor level, neither of which are practical. The UFH would be used intermittently for comfort (walking barefoot), helping to dry the floor and prevent damp underneath and behind the kitchen units. The room will continue to be heated using radiators.

 

Is 6cm enough to install UFH?

 

Should in use a wet or electrical system ? I already have wet UFH in other parts of the house, so I should be able to tap into this.

 

Is it worthwhile and practical to install a very thin layer of insulation underneath the UFH if space allows and what type should I use considering the limited thickness?

 

Are there any precedents and guides for using vacuum insulation panels in this application?

 

[Redbeard]

Any insulation better than none at all, but 60mm for the 'whole sandwich' just seems far too minimal to me. Others may disagree...

[SteamyTea]

The calculations are pretty simple to work out the thermal losses to the ground.

If we assume that ground is at 10°C and the room at 20°C and the insulation has a k-value of 0.04 W.m^-1.K^-1, then:

 

U-Value = 1 / (l.k) where:

l= insulation thickness

 

U-Value = 0.7 W.m^-2.K^-1

 

So losses with a 10K temperature difference is 7 W.m^-2, so an extra 35 W for the full 5m²

 

So very little is lost to the ground.

 

Now the problem is really how hot will the floor actually need to be to heat the kitchen.  

[Iceverge]

Wouldn't bother with UFH to be honest, insulation will be the biggest gain for comfort. A warm surface covering and you'll be barefoot happy. 

 

Based on say 15mm adhesive + tiles I'd imagine about 75mm is your limit for total floor thickness. 

 

For me I'd do

 

3mm LVT

2mm adhesive 

11mm OSB 

11mm OSB

25mm EPS 200. 

DPM

25mm EPS 200

 

Float the OSB on the EPS, glue and screw all sheets with wood glue and 20mm screws.  Allow a little bit at the edge for expansion. 

 

Sandwich the DPM between the EPS layers to protect it. Stagger all joints in the EPS too. You could use PIR but I don't trust it as much not to crumble after a few years. Espically at the edges of sheets. 

 

Use some filler in any small gaps and sand the top layer of OSB if needed to get it perfectly flat. 

 

Glue down some LVT tiles. 

 

U Value about 0.6W/m2K before you take any of the ground resistance into account which is very worthwhile.

 

 

 

 

 

 

 

 

 

 

 

 

[JohnMo]

47 minutes ago, Iceverge said:

Wouldn't bother with UFH to be honest, insulation will be the biggest gain for comfort

Yep, 60mm wouldn't bother, get a pretty radiator.

[Nickfromwales]

Fit 50mm XPS tile backer boards for insulation, and you will get a free DPM and a floor that no longer feels stone cold.

 

You cannot use UFH to dry out or combat damp! Using a good quality liquid DPM (aka black jack) will stop the damp with ease, subject to you removing the 60mm of screed, applying the liquid DPM, and relaying 'whatever' back over it. 

[Iceverge]

There's rads there already I think. 

 

One thing that doesn't get mentioned much is plinth heaters. 

 

You could get the cost toes feeling without all the pipes etc. 

 

Has anyone used one?