Is this a valid construction method (insulated slab/DPM/XPS/underlay/floor)?

[anarres]

In my office outbuilding I have a well insulated slab foundation approx 30m2 (200mm XPS under 170mm concrete, with DPM) which is fairly level (up to 10mm dips in 2 places).

 

I have 75mm to make up to final floor level. I was wondering if instead of screeding (which would be a significant PITA), if I could instead do the following:

 

Level the slab with something like Mapei 1210 leveller (for 1mm to 10mm)

add DPM (standard 1200 gauge poly, up the sides and taped to existing DPM for slab)

add 50mm XPS (e.g. Danopren)

add 5mm high density underlay (for sound reduction mainly)

finish with floating engineered wooden floor

 

As I understand it the reason to screed is to make the floor level and it it is not a structural layer, so not technically required. I guess my main question is if I can use 50mm XPS and then another underlay on top - because I'm not convinced XPS by itself wouldn't cause significant noise issues as it is so rigid.

 

If I can do this, can/should I glue down the DPM and/or the XPS to make it firmer? Perhaps if I lay the XPS correctly it would not be able to have any movement anyway but I've not found this construction method anywhere so I'm scratching my head a bit...

 

[Alan Ambrose]

I wonder whether the XPS will go down exactly flat - I'm not sure I think it will. Maybe a thin layer of ply to bridge point loads and smooth?

 

I have something like that in my workshop - actually 'horizontal timber framing' with insulation between and ply over. Can't remember how I came up with that - probably to support the edges of the ply sheets. I was expecting some fairly heavy localised loads for machine tools.

 

Be aware that 'self-leveller' doesn't - it needs some skilled help. Apologies if you already know this.