Slab styrofoam insulation type for in floor heat

[Tracs]

I'm inching closer to starting my 40x60 shop.

Manitoba, Canada. -30f winters, 90f summers.

Heated floor.

I've lined up a concrete contractor to construct the thickened edge slab and he wants me to have the material on site for first weekend in August.

The material quote shows Styrobar Plus 4x8-4" Type 2 - EPS R16.16.

The engineers drawing of the slab shows 4x8-3" Type 4 - XPS R15

There is about a $1000 difference between the 2.

Taking into consideration slab heat retention, heating costs, initial purchase costs, and assuming both are acceptable, what is the benefit from one to another?

 

[WildBill]

I thought you wanted XPS for foundations because it's waterproof and stronger. And some other reason I can't remember. But I'm not an expert. I did use it for slab insulation on my shop after reading about them. Here's an article about it. https://www.soprema.co.uk/en/articl...isture, XPS,apply without irritating the skin.

 

[jack stand]

Just call your concrete guy and talk about this discrepancy between the two. It might just be a simple mistake.
I'd think that a thicker insulation (4") around your thickened edge detail would pay off with the 3" in the field.
I see "styro" in the name and think white, coffee cup foam. That's fine but it's less r value per inch but it's less expensive and it's made up with using a thicker sheet. AFAIK the only foam not recommended (under grade) is p-iso, it's hydroscopic - absorbs water.
Give your guy a call and see if this is his recommendation.

 

[ConCretin]

You can use either XPS or EPS as long as it meets ASTM C578. This is a pretty good article on the subject.

https://www.concreteconstruction.net/how-to/site-prep/choosing-between-eps-and-xps-rigid-insulation_o

XPS seems to be more common in commercial construction but its higher strength isn't really needed for residential applications (or most commercial ones for that matter.).

 

[WisJim]

Which is more expensive? EPS is the usually white expanded foam, similar to the white foam coffee cups. XPS is extruded foam, like Styrofoam brand blue sheets or the pink or yellow from other companies. They are all acceptable for under a slab as long as they meet the compressive strength requirements.

 

[kj_mustang]

And the problem is usually finding the higher compressive strength EPS foam sheets. I gave up and bought XPS locally.

 

[Tracs]

You can use either XPS or EPS as long as it meets ASTM C578. This is a pretty good article on the subject.

https://www.concreteconstruction.net/how-to/site-prep/choosing-between-eps-and-xps-rigid-insulation_o

XPS seems to be more common in commercial construction but its higher strength isn't really needed for residential applications (or most commercial ones for that matter.).

It appears the Styrobar Plus EPS does meet ASTM C578.

It is also made somewhat locally, to my surprise.

The specification sheet shows:
Styrobar Plus 22 is suitable for exterior and interior
sheathing above-grade, and below-grade applications
in Canada such as; under-slab, grade beam, perimeter,
radiant floor heating, frost shield protection and back
fill.