Would anyone recommend using an 8" core or is a 6" core sufficient enough to build a two story home in the state of Arkansas.  Please advise.

6" is sufficient for two story construction of single family dwellings. There may be some exceptions. We do most of our building above grade with 6" forms. We worked on a 4 story motel here in GA. and all forms were either 6" or 5".

Am building a two-storey house in Manitoba and builder recomends 8" for basement walls and 6" for upper walls.

You really need to talk with an engineer of record. There are so many points that must be understood before anyone can make a determination. Some questions would be  1)basement?, 2) fill to what height? 3) soil type? 4) window arrangement between floors, 5) steel spacing/size/grade.

Patrick T.

Ebuilder,

Patrick is correct that a local engineer would be your best resource. Here in the Pacific NW where we are in the worst siesmic zone and building on sand which has the worst carrying capacity, we are building a 4 story 6" core condo with concrete floors, concrete roof, and cantilevered concrete decks. So it can be done but you need to find an engineer that is comfortable with concrete construction. Engineers are like doctors they specialize in certain areas. You could go to a general surgeon for back surgery butt your results would vary greatly from going to a neurosurgeon.

ICF Contractor