Do I really need a second layer over routed OSB

[ricardo100671]

Hi

 

We are considering installing underfloor heating in prerouted 22mm OSB boards. Originally Underfloor Heating Store Quoted for ProFloor 22mm boards and we designed all our floor levels and door height to this. Now they have offer a new board, also 22mm, but foil faced and closer spacing, saying these are more efficient, which I guse makes scense. However they say you also now need an additional 6mm over the top before laying floating floor. 

I can understand for carpeted areas, but do I really need teh extra 6mm board, if we will be floating 12mm engineered flooring over. Would it not also be more efficient without.

 

Thanks in advance.

 

 

[torre]

I think building control will insist on the extra board over. It forms part of the structural floor - you might be okay with 12mm flooring over but the next occupant may replace that with just carpet, unwittingly making the floor unsafe

[G and J]

8 hours ago, torre said:

I think building control will insist on the extra board over. It forms part of the structural floor - you might be okay with 12mm flooring over but the next occupant may replace that with just carpet, unwittingly making the floor unsafe

Is that to ensure that there’s enough strength in the floor ‘skin’ to stiffen it nicely?  

 

If so a floating layer of flooring won’t help.   Presumably that extra strength could come from an extra layer under the routed OSB just as much as it could on top, perhaps improving the thermal performance. 

[torre]

Putting the extra board below is probably problematic in terms of heat distribution (in the future carpet scenario) though I agree it'd give the same support.

Best would be clarify with the board manufacturer though it sounds like they've already said it's needed

[G and J]

26 minutes ago, torre said:

Putting the extra board below is probably problematic in terms of heat distribution (in the future carpet scenario) though I agree it'd give the same support.

Best would be clarify with the board manufacturer though it sounds like they've already said it's needed

Ah - do you mean ‘cooked’ stripes in the carpets.  That does not sound good.   

[Iceverge]

12mm seems very thin for engineered flooring. 

 

I suspect it's 12mm laminate you mean? 

 

In that case you could just swap it out for 6mm LVT which I would prefer anyway. 

[saveasteading]

Is this on a solid floor or over joists?

[ricardo100671]

On 06/11/2024 at 09:32, saveasteading said:

Is this on a solid floor or over joists?

It's Over Joists and we will be floayting 12mm Laminate

[saveasteading]

Can we see the whole cross section from ground to floor surface? Words or pictures 

You need structural support and insulation within it.

[RJF]

^{Might be a bit late, but on my experience. Undefloor heating without a screed is money down the toilet. I allways sugest at least 18mm screed board over it.} 

Edited February 20 by RJF

[JohnMo]

7 hours ago, RJF said:

^{Might be a bit late, but on my experience. Undefloor heating without a screed is money down the toilet. I allways sugest at least 18mm screed board over it.} 

Yes would agree, have both screed and covered with osb. The osb required such high flow temp to keep room remotely warm, I decommissioned.

[Big Jimbo]

2 minutes ago, JohnMo said:

The osb required such high flow temp to keep room remotely warm, I decommissioned.

That makes sense, as timber will be much less of a heat conductor than screed.

[Nickfromwales]

9 hours ago, RJF said:

^{Might be a bit late, but on my experience. Underfloor heating without a screed is money down the toilet. I always suggest at least 18mm screed board over it.} 

I’ve done a few where it’s just spreader plates between Posi joists, then 22mm P5, then 6mm plywood, then adhesive and tiles.

 

Worked very well but the caveat is the higher flow temp.

Would be ‘ok’ with carpet too I guess, so I disagree that UFH without screed is money down the toilet, just needs to be done properly. I always make sure the plates are in full contact with the deck boards which makes a huge difference, and on the aforementioned one I used an air stapler to tack the plates to the underside of the P5.

[JohnMo]

23 minutes ago, Nickfromwales said:

UFH without screed is money down the toilet

It's ok if you have radiators elsewhere then you can run everything at the same temperature, but UFH at radiator temps is a waste of time and money. I ended with a fan coil.

 

Room with UFH on 125mm centres. 250mm of insulation underneath. At zero Deg day, flow temperature  over 40 Deg and room only getting to 16 degs. Pretty pathetic. Fan coil at 35 degs, any temperature I want in the room.