Insulating Floor and side of Foundtion

[ckrzysko]

I have radiant floor heat in my attached garage. I used Double bubble on the floor and insulated the wall with 1 inch but didn't go up the foundation wall. So the concrete goes to foundation to foundation.

My question is two parts: I'm building a detached garage and was wondering if anyone ever put down 2 inch 4' x 8' - 250 series Owens foam board under the slab? I already have the 2 inch foam board on the foundation going to sill plate. My concrete guy tells me to leave it and then cut it back to the slab height. He stated, This will stop the floor from wicking to the outside wall. Friends tell me to just put it down on the floor and leave the sides as is. This method the 2 inch foam board is not showing around the perimeter.

Should I have the concrete guy pour the slab with insulated side walls or have the slab poured on top of the foam board (not exposing the foam board)?

Is 2 inch foam board overkill on the floor?

Thanks you for your input!

 

[OldNeons]

I would definitely insulate under the floor even if you aren't heating it. It makes a big difference! Make sure you maintain a thermal break between the foundation/outside concrete and th floor slab. You don't want conductivity bringing the cold in!

 

[K'ledgeBldr]

I think this should answer your question-

https://buildingscience.com/documents/insights/bsi-059-slab-happy

 

[Radix2]

Where are you located? Hard to get good advice not knowing if you are building in Arizona or Minnesota...

 

[rburke65]

Do a search for radiant floor heat. Asking if anyone has ever used 2" foam board under their concrete floor is like asking if anyone has ever used asphalt shingles on their roof. Yes it's been done thousands of times.

 

[ckrzysko]

Where are you located? Hard to get good advice not knowing if you are building in Arizona or Minnesota...

Live in the northern Illinois.