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Rigid Insualtion Under Slab

Rigid Insualtion Under Slab

Rigid Insualtion Under Slab

(OP)
I am working on a "oh, by the way" project, you know, the ones where the client says,"oh, by the way, we are going to be doing xyz and I hope you are OK with this".

In this instance, the client is going to be putting 60psi compressive strength rigid insulation under the slab on grade and is asking me if this is OK. While this would normally raise a few eyebrows on my end, in this instance, we have some large moving loads on the slab and I am a bit worried about it. The slab was designed in accordance with the geotechnical report which gave a subgrade modulus of 200pci. I can't seem to find anything that will list either a subgrade modulus for the rigid insualtion or an equivalent E value.

Of course I am also getting the "we did it on a similar project so I don't get why you are so worried about this" from the client as well.

Does anyone have experience with adding rigid under a slab on grade?

RE: Rigid Insualtion Under Slab

I know its done all the time but I don't know if I will ever be comfortable with it. Seems it would be sensitive to the quality of the installation as far as flatness and smoothness of the sub-base otherwise you might get some bridging.

I had a foam "BTW" the other day on a house I am working on. "BTW, we are cladding the house in 1 1/2" foam and 7/4 (yes 7/4!) reverse board and batten. Tell us how to fasten it!"

RE: Rigid Insualtion Under Slab

Typically when we do insulation under a slab, we`ll put it on a 3"-4" mud mat. This is an unreinforced slab that provides a flat, smooth subbase for the insulation. In freezer applications, glycol or electric heating elements are run through in mud slab.

RE: Rigid Insualtion Under Slab

Generally use Type 4 or Type 6, Extruded Polystyrene... Dow Hi-40 or 60...

Dik

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