Overbuilt concrete slab with Rigid insulation

[tonyiggy]

I have an elevated concrete slab, where a portion of the slab has a finished floor elevation that is 4' higher than the top of the slab elevation. Due to column locations, the easiest thing to do is the overbuild ontop of the structural slab. I have considered a few options, One option is building up 3.5' feet or so with rigid insulation and then pouring a 5" LW concrete slab on top of it to get to the F.F elevation. Is there any long term deflection issues with this option? by my calculations with a 100 psf LL 40 psi rigid insulation should be good enough.

Thanks

 

[KootK]

1) I've done similar things in the past successfully, albeit only for relatively small areas of floor.

2) The strength and stiffness of appropriate rigid insulation can well exceed that of the soils that typically support slabs on grade.

3) For long term deflection, you'll want to keep your loading well below that which would induce meaningful creep in the rigid insulation. This is pretty easy to do in practice and the manufacturer of the insulation that you go with should have recommendations.

4) It would be good if moisture didn't make it's way into the insulation cavity.

 

[Enable]

In the restoration industry we use rigid insulation fairly frequently to make up elevation differences. But for any application where long-term creep can be an issue, we use HL-100. If creep is not an issue and we are substituting for weight only, we use HL-40.

Insulation is quite expensive and depending on the size of the area, I am sure cheaper alternatives exist.

 

[XR250]

I have designed metal stud kneewalls with metal deck in similar situations.

 

[tonyiggy]

Thanks for your input. This has been helpful.