Edwardian solid floor refurb

[amin]

I'm refurbishing the floors on my Edwardian house. I've removed the old timber suspended floor and looking to put in an insulated floor with UFH. I have about a 350mm-400mm void and ideally don't want to dig to far below this. The original slate DPC is about 150mm below floor level. 

 

I have two options and wanted to validate what works:

 

Option 1: Foam glass aggregate (bottom up):

250mm Foam Glass aggregate compacted

75mm Sand Cement Screed (with UFH)

Total build up 325mm
 

I'm considering option 1 because of the level of the DPC being below floor level and bridging it with any other options - but maybe i'm overthinking it?

 

Option 2: 

100mm Compacted Hardcore

DPM lapped to wall and above screed
200mm EPS

75mm Sand Cement Screed (with UFH)
Total build up 375mm

 

Option 2 does it work without a concrete layer and is the hardcore enough? There are some posts on here that suggest concrete isn't required and the hardcore might be enough? Also what about the fact that the DPC might be bridged in this setup?

 

Any advice and thoughts on these options will be appreciated!

 

 

[Mr Punter]

Option 1 may need a DPM.  You normally put a thin sand layer over hardcore to cover the sharp bits before you lay the DPM.  Is foam glass expensive?

[Nickfromwales]

6 minutes ago, Mr Punter said:

Is foam glass expensive?

Yes, very.

 

Clients architect spec’d it to go around the subterranean parts of a walk out basement, and I remember them raising an eyebrow or three when the builder quoted for the quantity needed. 
 

I still think two layers of EPS would have done the job perfectly well, but their architect and SE were setting fire to money at an extraordinary rate of knots, and what they came up with was usually a pile of shite.

 

Foamglass wouldn’t take kindly to being compacted either. 

[amin]

I'm thinking about the aggregate version of foam glass so this stuff which can be compacted. Also supposed to be good with moisture so DPM doesn't always seem to be necessary. 

 

Price wise I don't think theres much in it between them - the foam glass might be marginally more.