How To Raise Floor Level?

[subzero]

Hi we have an area approx 25m2, 10m2 is a new concrete floor forming an extension to the original. The original flagstone floor area was covered in very uneven concrete on top of which was a layer of very dodgy slabs, so we've had to remove these top two layers.

We need to bring this original floor back up to the level of the new extension floor but not sure how to go about this in the best way. The difference in levels is about 2 or 3 inches.

Ideally we'd like something along the lines of a timber frame screwed down to the original floor with celotex in the gaps then plyboard on top, but we've been told it wouldn't be possible to tile directly onto that as the tiles would crack.

Appreciate any advice.

 

[Chri5]

What you propose is no different to any other suspended floor, so I'm not sure why you have been told that laying out thick batons as joists and then fitting a decent thickness of plywood and then tiling over would lead to cracking.

It won't provided the batons are secure, the plywood fixed correctly and a suitable tile adhesive with some flexing properties is used.

Has the floor got a damp proof course?

 

[subzero]

Thanks for the reply. The area of floor we are talking about is currently covered in flagstone type tiles and under that i presume the original foundations of the house (1930's) so not sure what if any DPC exists..

 

[kjacko]

When we had to raise our 22sqm extension subfloor to the level of our existing kitchen, we used 25mm polystyrene underneath 18mm (or 22mm depending on how much depth we needed to make up) t&g moisture resistant chipboard. Then 4-6mm ply boards screwed down.
Karndean was then laid on top of that for a perfectly flush finish all the way through.