Slab main floor on top of ICF foundation

[MN_JohnH]

I am wondering how I would set up my main floor to be like this picture, ICF foundation walls with slab floor sitting partially on top of the ICF but inside the main floor wall framing. The double treated sill plate is total 3" thick so the bottom of the 4" slab goes 1" below the top of the ICF wall.
Can this be set up or do I just have do do it with a CAD detail?

[tundra_dweller]

You just have to adjust your floor heights accordingly, and you'll probably get a message about a negative ceiling height in the foundation that you can ignore. Also changing to 3 bottom plates in you ext wall main layer, and adding your 4" insulation to the foundation floor structure. And there'll be some CAD work for the cross section but nothing too major.

 

Here's a sample plan with how I was able to do it.

MNJohn.zip

[MN_JohnH]

12 hours ago, tundra_dweller said:

You just have to adjust your floor heights accordingly, and you'll probably get a message about a negative ceiling height in the foundation that you can ignore. Also changing to 3 bottom plates in you ext wall main layer, and adding your 4" insulation to the foundation floor structure. And there'll be some CAD work for the cross section but nothing too major.

 

Here's a sample plan with how I was able to do it.

MNJohn.zip 654.34 kB · 17 downloads

Thanks Sir, this is awesome. I am studying it to figure out exactly what you did but this is great, I really didn't think it could be done.

[tundra_dweller]

You betcha. Here's a step-by-step.

 

In your foundation defaults, set your slab to be at top of stem wall.

 

In your exterior wall type definition set the main layer to have 3 bottom plates.

 

In your auto-built foundation room DBX set floor-to-SWT to -3" and ceiling to -3". Note that in the plan I attached earlier, I didn't change the ceiling to -3", so it caused the floor to move up to 3" elevation instead of 0". The detail where the slab meets the ICF is the same, but setting the ceiling to -3" forces the top of the slab to stay at 0" elevation.

 

Open up your floor structure for the foundation room and add a layer of rigid insulation below the slab.

 

Edited February 14, 2025 by tundra_dweller

[MN_JohnH]

I am looking back at this as I have to do this again with a new plan. 
I have my floor plan done and now I want to arrange my floor to be as we talked about above.
So one questions is, how can I select all the rooms at once instead of having to do each room by itself?
And I am not getting the floor structure in an editable mode even on the sample plan here.
It seems the setting might have changed since this question was first asked.

 

Edited April 15 by MN_JohnH

[tundra_dweller]

Hi John, since the room in this case is defined as "Floor Supplied by Foundation Room Below", you would have to go to your Floor 0 foundation level to edit the floor structure.

 

As for selecting multiple rooms at once, I would try using the "Match Properties" tool on your edit toolbar once you select a room. You can then select from a wide ranging list of properties to narrow down your room selection as needed.

[MN_JohnH]

On 4/15/2026 at 7:09 PM, tundra_dweller said:

Hi John, since the room in this case is defined as "Floor Supplied by Foundation Room Below", you would have to go to your Floor 0 foundation level to edit the floor structure.

 

As for selecting multiple rooms at once, I would try using the "Match Properties" tool on your edit toolbar once you select a room. You can then select from a wide ranging list of properties to narrow down your room selection as needed.

Thanks, I guess I was looking at the main floor for settings.
 Makes sense. I will probably forget and need to ask again in a year.
For selecting the rooms I just made a backup copy then eliminated walls until there was just one room and the made the changes and copied and pasted walls back. In the past when I have gone through and selected rooms there would always be a closet somewhere that you don't see and then later on it becomes evident that things are messed up.
Anyway, thanks for the help.