Conservatory floor-18mm chipboard over 50mm insulation OK?

[elvira]

Urgent advice needed please.
The concrete slab was laid about 6 weeks ago and is close to dry now. I did not put insulation (50mm) under the concrete slab, as I wanted it to go on top of the slab. I decided to do this because I am having electric underfloor heating and I thought it would be more efficient this way, otherwise I would be heating up the slab.

After the concrete slab, a layer of self-levelling was applied to give a smooth finish to the floor level. This has been drying for about a month now with a dehumidifier.

I have bought 50mm floor insulation (polystyrene) and 18mm chipboard to lay on top. My questions are:

1) how should polystyrene be fixed to the concrete, & the chipboard to the polystyrene?

2) Can this floor be tiled with 60 x 60 cm porcelain tiles ?(I’ve read about risks with floating floors and tiling but presume the phrase “floating floor” applies when the chipboard is laid on joists, not when it is laid on polystyrene as in my case or am I wrong?)

3) Should I make my floor stronger by adding joists first with the polystyrene fitted between them. I really don’t want to do this as I prefer to avoid having any gaps in the insulation sheet.

4) Instead of joists can I make the floor strong just by adding a layer of tile backer board or plywood eg 3mm or 6mm?

5) I have had a demudifier since mid December to dry the concrete slab. The conservatory has been sealed with all windows closed. The floor does seem very dry now but I still get a bucket of water – could this be from the air. Whats the best way to know if it is now dry?

NOTE I can’t replace the 50mm insulation with screed because the insulation is required.

Many thanks for any advice.

[elvira]

Sorry, i made an error on my original posting. I am using 18mm flooring chipboard (not 22mm) and the insulation is Jablite Jabloor 70 (50mm).

[welsh brickie]

the polystyrene will be laid on the floor with no fixing required.
The t&g floorboards should be glued heavily on the joints and laid on the insulation.No mechanical fixings required.
If you want to tile over it you will need to lay 6mm ply glued and screwed to the chipboard.