Hi,

I have a subfloor with wet ufh in place already and will be having engineered parquet laid over the top soon.

The blocks seem to come in 10mm, 15mm and around 20mm thicknesses. I’m wondering which thickness is best? I’m guessing the 20mm thick blocks take longer to heat up but perhaps retain their heat for longer so are better overall? No idea hence the post here.

My kitchen/diner has a new solid floor with around 150mm of insulation and around a 45mm screed layer ontop. The rest of the house has a suspended timber floor with around 75 mm of PIR insulation between the joists and then the ufh laid in about 20mm of a dry sand and cement mix on top. This is covered with Knauf Gifa board which is 18mm thick and has very good thermal conductivity (about 4 times that of a a chipboard subfloor).

I’m thinking the 10mm blocks may be just too thin (they have the same wooden wear layer as the 15mm blocks) and so not very strong and that the 20mm blocks are unnecessarily thick. So leaning towards the 15 mm block, does anyone have any experience, good or bad?

We like the 'tumbled' look which is when new blocks are thrashed around in a mixer with stones to knock the edges off them and make them look a little older. In order to survive this process most tumbled blocks are around 20mm thick. 15mm tumbled blocks can be bought but there is less choice.

Any experience appreciated.

Thanks DJH, I have been considering that. The 20 mm thick blocks have the most wear layer - as you might expect. I’ve found the 10 and 15mm blocks seem to have the same thickness though of around 4mm solid wood on top. This I believe allows around 3 sanding events. I gather most people seem to lay their floor and never sand it though.

So in that (wear) sense some of the blocks are the same, hence I wondered if there was any appreciable difference in warm up and cool down periods and the amount of gas required to heat the room between them all.

FWIW, I've got 18mm non-engineered (solid) T+G oak over low temperature UFH (pipe at ~90mm spacing in thin sand-cement screed - mixed with water reducing agent). Flooring is glued down with ms-polymer adhesive.

Max water flow temperature is 40C (gas CH, direct connect to boiler no mixing valve or secondary pump). The floor has been down about 9 years with no problems.

With the even and mild temperatures from the UFH and bonding, there's not really any problem with it. By Feb the gaps between the boards open up about 1mm or so (coinciding with min humidity in the air and min water content in the boards I assume), but there's not really any more movement than you'd expect without UFH.

On that basis I'm planning to have solid 10mm parquet fitted in the kitchen next year (just doing EWI at the moment, so heat demand and therefore flow temperatures will drop a bit further - kitchen refit is next).

If you're in Sussex, and you'd like to take a look it's in Brighton.