New extension floor has sunk

[rajk]

Hi - I have got a floating wooden joist floor.

The joist are 6inches by 2inches. Covered with 18mm ply. Then I have got polyplumb overlay panels for under floor heating. Then ceramic tiles for finishing.

Its been just over a year and now the floor has dropped by about 1/4inch all round. Gap formed near skirting boards, splash back and work top.

Is this normal? Will it drop more?

Major problem is my tiles are cracking and I have got underflooring heating directly underneath the tiles.

 

[tony1851]

If it's a timber joist floor, its possible that the joists have shrunk due to the
u/f heating. This seems confirmed by the fact that the gap is all around the room, rather than just localized. As timber dries out, it can shrink considerably across the grain, and 1/4 " would not be surprising for 6" deep joists.
Its quite likely that the shrinkage is now at or near its maximum; its a pity about the tiles.