I'm getting towards the end of renovating and converting a bungalow. I'm looking to install wet ufh throughout the ground floor. The Kitchen/Diner has a new insulated floor which will have the pipes laid on top and then a 45mm flow screed poured over this. The plan for the rest was to lay the pipe ontop of rigid insulation (which I’ve already laid) inbetween the old joists leaving a small 25mm gap which I’ll fill with a dry biscuit mix of sand and cement.

My question is; If I lay an 18mm Ply subfloor on top of these joists, and then add an engineered parquet block on top of this, say 15-20mm thick. Is that too much wood for the ufh to work? Ie 18 + 15-20 = 33-38mm thick.

Most of the ufh companies say 18mm is the max for wood. But that basically rules out any parquet due to needing a sub floor beneath it. Yet every wood shop has an engineered parquet block of some sort for sale which they all say is compatible with ufh. How!?

Will it work and just take longer to heat up? Which I don’t see as a problem if I get used to the warm up times and adjust the timer, Does it therefore also take longer to cool down? Or will it just not heat the room?

Does anyone have any experience of engineered parquet blocks with a subfloor beneath and ufh?

Many thanks.

Where can the heat go?

How much insulation is there underneath?

What do you call high flow temperature

I have a friend who put is ufh above the ceiling of the room below and insulated under that with 100mm rockwool 40mm pir and double plasterboard

Advisers said it wouldn’t work, but it does — where else can the heat go

Choose your engineered parquet block and then ask the manufactures for their recommended layup with UFH.

Posted By: djhBack to the boiler and turn the boiler off.

That's what "the UFH cannot deliver enough power to heat the room up" means, I believe.

Think about it at the extreme - if you run a highly insulated pipe with hot water around the house you will get minimal heat loss from the pipe and drop in the return temperature will be minimal. The w/m2 of the floor will fall below the heat losses from the room. You normally balance that either by running the pipes closer together or increasing the water temp but neither will work if you have too much 'insulation' between the pipes and the room.

Posted By: HoveTomYet every wood shop has an engineered parquet block of some sort for sale which they all say is compatible with ufh. How!?

Will be fine if you lay the parquet on top of screed rather than on top of timber...

Some years ago on one of the building forums someone posted about problems they were having with their UFH. It transpired they had used aerated screed instead of regular.

An update..

After some online research I found Knauf Gifa floor dry screed boards. They come in various thicknesses but the 18mm thickness is also structural, it’s called Knauf FHB 18 ( unlike many other dry screed boards).

The thermal conductivity for FHB is 0.44 W/mK, I believe that 0.13 is the general value for timber products, so the FHB is 3-4 times more efficient for thermal transfer in comparison.

It’s expensive stuff, around twice the price of Chipboard flooring although if budgeted for from the outset could be worth it. However I managed to find some on eBay at less than half price. It arrived today on two pallets. It’s heavy!

It’s not designed to be screwed down to the joists, I assume to allow for thermal expansion, instead it’s glued tongue and groove and then a floating floor, above the biscuit mix of sand/cement on the suspended timber. As it’s about twice the weight of comparable timber I don’t think it will budge. Knauf technical folk advised this is fine.

Has anyone used this product? I’m hoping it will work great with ufh and allow a bit more flexibility with regard to the finished floor on top.