Concrete pad patio - Celotex type insulation?

[mikeinthemidlands]

Hi guys

Quick question, would Celotex type board be OK to use under a concrete pad outside? Reason I ask to raise the level up 75mm will cost a lot less and use less concrete as I need to raise nearly 200mm.

If so do I need a DPM underneath and on top of it? The final finish is a porcelain tile.

Cheers
Mike

 

[Tigercubrider]

Not qualified but where I used to work they had a covered way that linked detached buildings. The covered way was in fact a duct for cables and pipes, with access from a cellar type stairway. You could stand up in it and it was easily 3m wide.

At some point they needed to change the door entry to be DDA compliant. There had been a step before.
So before each doorway they intended to add 6" of concrete and slope down on either side

Apparently the structure underneath (i.e. The deck of the covered way) was too weak to take the weight of the wet concrete so they added polystyrene (of celotex?) to minimise the weight

It's still ok ten years later but check the filler material

 

[Notch7]

Jabolite or xps?