Doubt on thermal insulation on concrete floor (Part of renovating the whole of house)

[vineeth]

Hi All,

As part of the house renovation that we recently bought, we are trying to add an engineered floating floor with insulation in a room (5.5m by 3.4m, around 30 years old construction) with a screed-ed concrete floor. From the looks / feel of it, there is no insulation on the floor.

My plan is to add a damp proof membrane (Not needed since the concrete is pretty solid and old, but does not hurt I guess) followed by a rigid insulation (Celotex TB4000 12mm or similar), and then lay the floating floor straight above it.

1. Do I have to pin down the insulation board (Washer with screwed down to the concrete or glued down)
2. Do I need to add a thin layer of ply (If so what width should it be) between the insulation and the floating floor.
2a. If not how would the floating floor behave around edges where the insulation boards meet? Won't it sag?

Thanks in advance

 

[endecotp]

(Celotex TB4000 12mm or similar)

Do you mean 12mm thick? That won’t do much!

then lay the floating floor straight above it.

1. Do I have to pin down the insulation board (Washer with screwed down to the concrete or glued down)
2. Do I need to add a thin layer of ply (If so what width should it be) between the insulation and the floating floor.
2a. If not how would the floating floor behave around edges where the insulation boards meet? Won't it sag?

Celotex and/or Kingspan have documents telling you how to do this, e.g.
https://az750602.vo.msecnd.net/netx.../22173_ProductBrochure_ThermafloorTF70_UK.pdf
See figure 8 and the text on page 11 in that document for what you’re proposing.

You need something like an 18mm layer of chipboard / OSB / ply over the insulation.

 

[vineeth]

Thanks @endecotp

I thought the 12 mm has got good thermal insulation specs?

 

[oldbutnotdead]

To meet current standards you're looking at 100mm of the stuff- the thermal conductivity (or resistance if you like) is proportional to the thickness.

 

[vineeth]

Ah okay, unfortunately cannot go beyond 12 or around that as it will reduce the height of the room considerably

 

[oldbutnotdead]

That figures. Given you'd need 18mm OSB or similar on top of it anyway then your 12mm isn't going to work either- so your choices are hack the floor out & relay or (what I'd do if the concrete is in decent nick) DPM, underlay, floating floor.

 

[Notch7]

Thanks @endecotp

I thought the 12 mm has got good thermal insulation specs?

Compared to other materials 12mm thick, yes.

but typically extensions are built now with 70mm - 100mm of floor insulation below the screed, so compared to that 12mm isnt much.

I guess 12mm would be much better than nothing though!

 

[vineeth]