Insulating under screed

[akist]

What materials could I use under screed to make up extra depth, other than or in addition to rigid insulation? Concrete slab is not level but is 230mm below FFL in places. With 100mm insulation and 60mm screed, this would require and extra 70mm fill in. Rigid insulation is very expensive and maybe cheaper filling in with extra screed.

 

[23vc]

More concrete, or go 150mm PIR and 80ish screed? There’s going to be a cost however you do it

 

[23vc]

Or possibly the jablite/cheaper insulation?

 

[HERTS P&D]

Go with the 150mm PIR, can't beat extra insulation!

Andy

 

[jeds]

As 23vc says, if you have an excess depth to fill, 300mm EPS insulation will cost approximately the same as 150mm PIR insulation - thus achieving the same result - but saving on alternative infill material. On the other hand, Herts is quite right, these days it makes sense to increase overall insulation.

Just one thing; if you do increase EPS instead of PIR, make sure the EPS is the correct quality and is suitable for the depth? There are very cheap polystyrene insulations available but they are not the correct density for large depths.

 

[akist]

I am getting 150mm expanded polyurethane EPS70 instead of 100 PIR, and then screed at around 73mm avg depth.

I have a choice of non-cementinous "rapide" screen and cementinous rapid. Any reasons to choose one or the other?