underfloor heating wooden floor underlay

I have looked through the available threads concerning this topic already but they date back a few years and do not address my concern exactly.
I am about to buy a semi-solid tongue-in-groove ash floor for an extension with underfloor heating (200mm of insulation underneath). All the information I have found here and online (scattered and sparce) points to a floating floor which suits me fine. The issues arise with regard to the underlay. My concern is that the underlay would end up as an insulator rather than a conductor of heat and reduce the effectiveness of the heating. I know that the wood itself is not as good a conductor as stone or ceramic but should I be trying to avoid any additional insulators? From what I can gather, the foam underlay gives the floor a good feel underfoot and can eliminate air pockets were the floor to be floated without the underlay. If someone could suggest a suitable underlay I would appreciate it. I know that elasticon make a product called 'lock' which is for ufh floors but it seems to be aimed at click together floors rather that standard tongue-in-groove. Also, one floor shop gave me a sample of the underlay they use. It is 2 - 3 mm white foam but I have no idea whether it is a conductor or insulator. Lastly, should I also consider putting a moisture barrier over the concrete first (another heating hurdle?)
Thanks.

I have put in Junckers Solid Clip system floor (14mm thinckness) I had to put in polythene and underlay (from Junckers). I debated putting gluing the boards but the Junckers Rep advised me to clip then in. When my tiles are @ 27Degrees my wooden floor is at 23.5. So you can work out the % loss. If I was back again I would not have put in the polythene.

Groober,
I am in the same situation myself. I am finishing off a self build and have underfloor heating throughout the house. I have bought an Engineered Walnut floor for one of the rooms and plan on laying it tomorrow.I also looked into the underlay and found some underlays specifically for underfloor heating applications. I asked the rep what he thought was best for an underlay and his response was that they were a waste of money and that I should just use the foam and no polythene. I plan to go ahead and use the standard 3mm foam as (a) I don't have the time to wait for the special underlay and (b) I'm not convinced it will be much better.

Hi Boyler,
Just wondering if you trust the rep? I came across an underlay by Duralay called "Heatflow Wood & Laminate" which seems to be specifically for ufh. Also, my search today of a few flooring sites has brought up the use of a moisture membrane again. I have a feeling that the 3mm foam is probably fine also but would really like an authoritative answer. Best of luck with the floor.

I am in the same situation aswell, been to a few flooring places and they all give different answers.
One place tool me to only use cork underlay ( €2.63 per m2 ) with engineered flooring ( solid wood was out of the question )
Another place said " well you don't have to put any underlay if you don't want to " !!!
One place said they have an underlay which has lots of small holes in it to let the heat through
I was going to glue the flooring to the concrete as this would make sure there is good contact between the flooring and the concrete ( no air pockets ). But after thinking about it I'm not so sure as it would not allow the flooring to move independantly of the concrete with changes in temperature which could cause cracks

Still researching it, can't beleive how hard it is to get an answer ...

We laid a solid ash floor this past year on elastilon with underfloor heating and have no problems at all with it. No expansion issues in the timber thus far, and I was a bit careless a couple of times with controlling the heat. In fact the ufh was off a couple of days and no issues with when ufh was turned on again. There is a lovely "flex" feel to the timber when you walk on it. The boards are 5 1/4 inches wide and varying lengths. Perhaps this is your answer. We were scared in purchasing it and in fact regretted buying the elastilon at one point due to all the conflicting advice we were being given, but not now.

all the best, optimistic

Guju121 said:

I am in the same situation aswell, been to a few flooring places and they all give different answers.
One place tool me to only use cork underlay ( €2.63 per m2 ) with engineered flooring ( solid wood was out of the question )
Another place said " well you don't have to put any underlay if you don't want to " !!!
One place said they have an underlay which has lots of small holes in it to let the heat through
I was going to glue the flooring to the concrete as this would make sure there is good contact between the flooring and the concrete ( no air pockets ). But after thinking about it I'm not so sure as it would not allow the flooring to move independantly of the concrete with changes in temperature which could cause cracks

Still researching it, can't beleive how hard it is to get an answer ...

Click to expand...

Will have a look for that elastilon. That Duralay Heatflow looks promising too and they also do an underlay for carpets.

Optimistic, can you tell me if you used a moisture barrier ( 500 gauge polytine ), or is it necessary with the underlay

I'd say the cheapest skinnest underlay you can find.
I have carpet on some floors and its doesent stop the heat.

You have some serious insualtion in there - The heat can only go one place and that is up. Remember - even if it takes slightly longer to emit upwards it doesent matter as thee heat will be on all the time - so what doesent come up straight away keeps the piped water that bit warmer for longer.

Engineered wood is expensive and unneccessary.

I've seen solid walnut used and it works fine despite all technical advice saying not to use it.

Too much science on this one doesent help.

My lamnate floor was put down this week and I used cork underlay. Its very thin only 5mm so I dont think it will have much impact on UFH performance.
Generally I was told that solid floors were not suitable at all for UFH and that the engineered floor or laminate is the most suitable for UFH

Guju121 said:

Will have a look for that elastilon. That Duralay Heatflow looks promising too and they also do an underlay for carpets.

Optimistic, can you tell me if you used a moisture barrier ( 500 gauge polytine ), or is it necessary with the underlay

Click to expand...

No we didn't use a moisture barrier. We were also told not to use solid timber over ufh, but are delighted with the results this far.optimisitc

You need to get an underlay that is designed to be used with UFH. There may well be other underlays that will do just as good, but the floor and the heating system cost too much money to be taking chances.

That white 3mm foam is known as a ' closed pore ' underlay. It is designed to act as a moisture barrier. You need one that will act as a heat conductor. An underlay for UFH compatible laminate will work just fine.

A lot of carpenters don't like using the Elastilon, because of potential movement in the floor due to heat and moisture, even though it is supposed to be able to cope with those issues. However, your floor is still glued down, and you cannot be sure that the Elastilon will "do what it says on the tin".

If your floor is floated it can adjust itself if needs be. Just leave some room for expansion, the boards won't go anywhere. If they are stuck down, and they need to move, they will buckle.

again - its one are where the scientific theory of what is the 'right' way really doesent make much of a difference in reality - except leave you poorer.

dont buy these special ufh add ons. They are for snake oil for mugs.