Floating floor insulation

[boondocker]

Having lifted the bathroom flooring (18mm T and G chipboard) and the polystyrene sheet insulation underneath to run supply for new radiator, I noticed that some of the polystyrene is in pieces where a previous bath installation had taken place.

Thinking that this might be a good time to lose some of the surface pipe work ( hot and cold to bath, basin and WC) beneath the floor around the edges and therefore the need for boxing I will need to replace some of the 'damaged' polystyrene sheets to make good. Trouble is the sheets are

48mm thick and new ones from the sheds are all 50mm. This 2mm is a PITA as it will cause a height difference when the boards are replaced.

Does anyone have any ideas or comments?

[Tim Watts]

On Saturday 12 January 2013 10:30 boondocker wrote in uk.d-i-y:

I bet they were 50mm thick when they went in.

Tricky - not sure what to suggest...

[Roger Mills]

Maybe one or more of:

- replace all the insulation with 50mm

- use thinner board over the new insulation

- lower whatever it is that the insulation sits on

- lay some 2mm sheet material over the part of the floor which you

*don't* re-build

Is this a ground floor bathroom with a solid sub-floor? If not, what's under the slabs of insulation?

[alan]

In that case buy some 50mm and before fitting sandwich between 2 flat sheets of wood/chipboard with some heavy weights on top.

[Tim Watts]

On Sunday 13 January 2013 12:51 alan wrote in uk.d-i-y:

Might not be that easy. I've seen jablite compress over a decade or more with percussion loads - eg by doorways.

I can make celotex a bit thinner by thumping it - but only at impact points. Conversley I can walk on unprotected celotex with no permanant deformation.

[boondocker]

Thanks for those suggestions. The flat is a first floor flat with a concrete subfloor. Thinner board might be an option if available, as would laying 2mm board over the non-rebuilt area. Either option will mean a weak point where the different thicknesses of insulation/board butt up against each other which may cause issues with the final floor covering which is another question entirely!

In fact, as the floor moves so much I'm really struggling to find a suitable floor covering at all.