Is 100mm PIR enough for UFH?

[connick159]

As title.says, have an extension started and slab 100mm slab already gone down. Plans are for 100mm PIR and then 50 mm screed. Have we blown it for UFH by only allowing for 100mm insulation?

[Onoff]

Any insulation is better than none. Just your heat losses will be greater than if you had say 160mm pir. 100mm doesn't meet building regs I don't think...whoever did the plans should have known...is there a bco overseeing this?

[wozza]

100mm PIR should achieve a U value of around 0.15 according to the Kingspan calculator (See link below - there are others available)

 

I believe that the recommended values for a domestic extension floor in England are a U value of 0.22, new build is 0.11 - this will need confirming

 

I did have the same floor make up, 100mm concrete, 100mm PIR, 75mm sand cement screed, however I have now changed this to 100mm concrete, 120mm PIR and 55mm liquid screed as I am also having UFH.

 

Kingspan calculator: https://www.uvalue-calculator.co.uk/calculator/floors/ground floor/solid concrete - insulation below screed/1/100/

 

 

 

 

Edited September 1, 2019 by wozza

[Nickfromwales]

Do building regs shift if you have / don’t have a heated slab?  

[Ian]

5 hours ago, Nickfromwales said:

Do building regs shift if you have / don’t have a heated slab?  

No

[Ferdinand]

7 hours ago, connick159 said:

As title.says, have an extension started and slab 100mm slab already gone down. Plans are for 100mm PIR and then 50 mm screed. Have we blown it for UFH by only allowing for 100mm insulation?

 

Building regs are 0.18 min. for extension floor.

 

Can you take a bit off the ceiling height?

 

You could perhaps consider a floating floor makeup with ufh overlay, and say LVL tiles, which would give you a bit more l.. but needs detailed comments from others.

 

Or go around the skirt with insulation.

 

I have less than 100mm pir and ufh. And it works. But it is now 10+ years old and I wish I had more.

 

Run the numbers and see if you are acceptably happy. It will be a OK, but there will be a hopefully modest cost.

 

My conservatory has 100mm PIR in floor but that has electric ufh really as a tick box for future buyers and is hardly ever used. The installers were planning 50mm and gave me another 50mm in all the walls and floor when asked.

 

Ferdinand

 

Edited September 2, 2019 by Ferdinand

[Jeremy Harris]

Building regs don't take account of the higher floor heat loss when UFH is installed, but perhaps they should, as warming the floor always increases the heat loss, so needs more insulation to counter this.

[nod]

I built an extension 7 years ago

The base had been a large conservatory 25 mil insulation

The customer was on a tight budget and wanted to retain the base

We full filled the cavity and put and loaded the roof joists with kingsman BC suggested we use the 18 layer multi foil on the underside of the joists 

If you are intending 50 mil screed you will have to use liquid screed or reduce the floor insulation further to allow for 75 mil semi dry screed   

[PeterW]

50mm with UFH is going to be tight anyway as that only leaves 34mm over the pipes unless you use one of the overlay systems. What is going on the top of the floor as final finish ..?

[connick159]

29 minutes ago, PeterW said:

50mm with UFH is going to be tight anyway as that only leaves 34mm over the pipes unless you use one of the overlay systems. What is going on the top of the floor as final finish ..?

Not sure of finish yet. Prob an engineered timber.

[dpmiller]

50mm is fine for many poured screeds, the one we chose requires a minimum 25mm over pipes.

[connick159]

1 hour ago, dpmiller said:

50mm is fine for many poured screeds, the one we chose requires a minimum 25mm over pipes.

Thanks, the ufh company near us said the same re the poured liquid screed. Another fella said he only does liquid these days. So much info out there to take in so this forum is a blessing.

It's 2 separate UFH areas - new extension will be in screed, old cottage will be overfloor. Although after reading on hear that these overfloor systems are pretty poor and lose a lot.of heat down into floor them i may need to dig up old cottagr floor and go inscreed too.

 

Edited September 2, 2019 by connick159

[Nickfromwales]

Thin Ufh / screed combos are quite erratic in how they convey heat into the rooms. 

Make sure you put the pipes at 100mm centres NOT 200mm or 150mm or you’ll have horrible over / under shoots ( room goes from cool to hot to cool to hot ) rather than the room staying comfortable. 

Choosing the room stats is also very important as the hysteresis needs to be 0.5oC minimum. Rotary ( thermostat-mechanical ) are utterly diabolical at running Ufh so choose well or suffer the consequences ?

[SteamyTea]

53 minutes ago, Nickfromwales said:

Make sure you put the pipes at 100mm centres NOT 200mm or 150mm or you’ll have horrible over / under shoots ( room goes from cool to hot to cool to hot ) rather than the room staying comfortable. 

Could you explain the reason for that?

[epsilonGreedy]

On 02/09/2019 at 08:04, dpmiller said:

50mm is fine for many poured screeds, the one we chose requires a minimum 25mm over pipes.

 

56 minutes ago, Nickfromwales said:

Thin Ufh / screed combos are quite erratic in how they convey heat into the rooms. 

 

 

There seem to be a conflict of interest and basic science with the trade now pushing thin flow screed for their own convenience.

 

Surely common sense favours opting for the higher heat capacity of 75mm screed and resulting better thermal stability?

[dpmiller]

I dunno, 12 tonnes of anything takes a wee while to heat up or cool down.

[SteamyTea]

6 hours ago, dpmiller said:

I dunno, 12 tonnes of anything takes a wee while to heat up or cool down.

Why I am questioning the pipe spacing, seems a bit counter intuitive to me.  But it may depend on the depth of the pipe and the temperature of the fluid.

[dpmiller]

Speed of response may well be a positive as well as a negative. Certainly, the supplier of our product thinks so

 

https://www.rtu.co.uk/assets/documents/Ultraflo-Heat-Response-Study-by-UU_180208_142848.pdf