polystyrene in concrete floor

[motorbiking]

I'm about to lay a concrete floor as a base for a home office and want to put 50mm of polystyrene in, with further insulation on top.

The regular polystyrene boards are not available for delivery.. But

Jabfloor 70 Polystyrene Insulation - 2400 x 1200 x 50mm | Wickes.co.uk

Jabfloor 70 Polystyrene Insulation - 2400 x 1200 x 50mm

www.wickes.co.uk

Is cheaper and in stock. Is this suitable with a 10cm concrete base on top. It will be laid on a DPM.

 

[freddiemercurystwin]

Yes that's OK to use, with a sealed vapour barrier on top, but why insulation bellow and above?

The barrier on top is more to prevent any concrete seeping into the insulation joints.

 

[motorbiking]

It seems no matter how thick you make the insulated slab, the floor is cold unless you also insulate above the slab. If you make the floating floor too thick it seems bouncy. Plus it's about 2x cheaper to have 50mm poly + 40-50mm celotex. The walls and roof will be 70-90mm celotex.

 

[Ivor Windybottom]

You'll need a vapour barrier under the top floor surface to prevent condensation, as your concrete slab will be colder than the room (although not as cold as the ground).

Celotex would be better - stronger and better insulating, and might cost only a little more.

 

[motorbiking]

Yes but there is a limit to this.. The last one I built. I used 100mm Celotex all round. The difference is tiny when you are heating and cooling a 12m2 space with an aircon unit. Particularly given the insulation massively exceeds the house.