Floating Floor over Phenolic Insulation Panels / Beam and Block

I'm looking for some advice on floating floor construction build up.

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As part of a renovation project for our ~'s built home, I want to insulate the ~70 m2 ground floor which is currently of uninsulated beam and block construction with a vented cavity. We are constrained on height of materials that can be added on top of the beam and block, mostly to match existing finished floor level at the bottom of the hallway staircase, but also to avoid shrinking the ceiling height (currently ~2.4 m above finished floor level).

So far, it seems like a ply (or other floorboard) sub floor floated on phenolic foam insulation panels will give best combination of thermal resistance, stack height, and cost. We would then add floor coverings, likely all vinyl tile with one room carpeted.

I've added a sketch of the proposed build up. I'm looking at using Kingspan K103 which has a compressive strength of 120 kPa at 10% compression.

The main questions I have are:

1. Is 18 mm ply going to be rigid enough to avoid deflections / point loads being transferred to the insulation panels? 
2. Do we need battens anywhere? So far thinking adding these in doorways, under kitchen units, and for bathroom fittings.
3. IS it necessary to factor in a 6mm ply layer on top as a "sacrificial" covering in case we go with glue down vinyl? Should this be fixed with screws?

Interested in thoughts on these points, and anything else I might be missing. If there are any general guides to floating floor construction would appreciate the share.

Edited May 28, by embra

Knock the concrete blocks out and replace with an EPS based system? I am not sure of the centres of the insulation based B&B systems so would need a survey for feasibility, but getting rid of the blocks would be a huge leap forwards. Have a look at BeamShield.

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When installing these types of 'floating' floors (like in a garage conversion) I always install 2 layers of 22mm P5 deck, glued and screwed and laid perpendicular to each other. Takes a washing machine on spin without blinking. One layer will be poor tbh.

Not quite an answer to the Q you asked, but perhaps to part of it. I have done a few 'pragmatic' floating floors on XPS (30 and 50mm), on PIR (25 & 50mm) and on rigid wood-fibre (200mm). In all cases I used 18mm T&G OSB ( x ) over, glued at all joints. You would have no reason to know that they were floating floors. They all feel so solid. I have never used phenolic in a floating floor.

The latest floor (the wood-fibre one) will have  final finished floor of T&G OSB too. I think that one might just break the 'floating' rule, in that I feel I might put a few screw fixings into the previous OSB layer.

I will start another thread sometime for recommendations on varnish for the 'finishing' OSB.

3 hours ago, ADLIan said:

IIRC phenolic foam should not be used under timber (ply/chipboard) flooring. Floor would need battening throughout to take it out of load bearing path.

Doesn't really seem a suitable product for a floating floor, unless the floor is otherwise supported and the insulation is just there to insulate. Seems PIR is the way to go here?

It's also not water proof / resistant, so the DPM would need to be hugely robust. Says it has a 2% shrink ratio too, so tight fitting boards will eventually become loose (if wedged in-between joists for eg) so seems the cons outweigh the pros here.

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