EPS compressive strengths

[BadgerBodger]

Hey, 

 

I’m looking to use EPS insulation (around 300mm) below by ground bearing slab within the existing structure. 
 

Having used the a Treanor Pujol insulated block and beam system I noticed that the “blocks” were EPS 70 but the overlay was EPS 100. 
 

It got me thinking, should I be using EPS 70 or 100 below by slab? 
 

There is a not insignificant cost difference (the lower density being cheaper) and my only reference point in having used EPS under a slab was a crew yard which was EPS 200 and when I used it as a void former/filler under a disabled access ramp which was EPS 100. 
 

 For reference the insulation will be laid onto “blinding” (old block paving) or compacted sand in two layers with the. DPM sandwiched between the layers to allow me to tack the UFH pipe work to the upper layer before mesh and pour. 
 

Badger 

Edited September 10 by BadgerBodger

[BotusBuild]

Badger,

What depth  and dimensions will the poured slab be? This may make a difference to what strength of EPS you require (hopefully one of the SE's will be along shortly, and they'll want to know anyway)

 

For reference, we poured a 250mm deep, 137m2 foundation slab with UFH pipes tied to the mesh. Our insulation was the Jackodur Atlas system (240 or 260mm thick), compressive strength of 130kPa if I recall correctly.

[Alan Ambrose]

The EPS grades are not so much density or a load bearing measure but ‘design load at 10% nominal compression’. That is, put 10 K N / m2 (approx 1 T/m2) on 100mm thick EPS100 and you expect it to compress by 10mm. So, what grade you need depends on what the load is and what compression you can tolerate. Probably a question for your SE in most cases unless this is., say, for a shed.

 

in true ‘ub fashion I’ll answer the question you didn’t ask - in that you might want to consider XPS (e.g. Ravatherm) rather than EPS as it has better long term thermal properties with time and moisture.

Design load at 10%

nominal compression

(kPa)

[BadgerBodger]

Interesting. Yes I had forgotten about this metric. I’ll ask my SE. 
 

It is around 90m2 (6x10) 100-125 thick (varies for to existing substrate and is easier to resolve with additional concrete) and is loaded with perimeter stud walls to FF and internal furniture including kitchen etc. 

 

XPS is even more expensive though no? 
 

At which point I might as well use PIR and build levels with stone?