18mm engineered boards over joists c/c joists - sub-floor ?

[justneedalittlehelp]

Hi, apologies if this has been asked before, and I've missed it, but I seek the wisdom of the forum ...

We've chosen an 18mm thick black walnut engineered board for flooring the ground floor of our house. This is described as 'structural' by the vendor and is comprised of a laquered 4mm wear layer over birch ply. I propose to lay this hidden nauled / screwed onto a suspended joisted wooden floor. The joists are on 450mm centres. There will be 100mm celotex or similar board insulation between the joists with a wet underfloor pipe network in the foil lined void above.

From my research thus far, it would suggest that 18mm boards shouldn't be used directly beyond 400 centres.

I am struggling to find the same finish / price in a 21or 22mm board and keen to keep the overall thickness down to help with the efficiency of the UFH.

Would it be viable to install this floor in conjunction with a thin ply under-deck to achieve the requisite structural stability ? Any guidance how thick would work ? Any underlay or measures recomended to aoid squeaks but not compromise the UFH ?

Thanks in advance.
Dave

 

[Floorsave]

Hi Dave,

If you have picked an 18mm walnut multiply, then it would probably be random in length.

The 18mm is seen as structural but the problem would be in the amount of fixing you will get as you will be laying straight to the joist. The floorboards that were originally there were probably ¾ or 18mm in depth. With ufh there would be more movement than in normal conditions so it would be advisable to try and get more fixings in each board.

Have you thought about laying a ply then floating the multiply flooring on top using a thin underlay? This means if you sand 2mm off the 4mm veneer the product with the ply should still be structural.