ICF Build with Main Floor Concrete
Last Post 02 Apr 2021 10:37 PM by GoGreenSelene. 4 Replies.
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RanManUser is Offline
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25 Mar 2021 01:49 PM
I have a residential build which is new to me.  There is a basement and main floor with roof trusses.  The house is in zone 5/6 going to be constructed close to, but not certified to Passive House Standards.  My problem is with a therm bridge on the main floor.

The build will include ICF walls from footing to rafter.  ICF walls have 7" of concrete with 2 1/8" EPS on each side.  The challenge in this case is the owner wants a 4" concrete floor on the main level with in floor heating.  I'm considering an ICF floor solution which creates "concrete beams"  Two vendors, Lite Deck and Quad Lock have such a system.  This system requires the basement wall to be completed first.  The floor panels are then placed to the inside edge (with lots of shoring) of the ICF wall which will connect the main floor concrete to the concrete walls.  Great supporting structure, but now we have a thermal bridge.

My understanding is that the ICF wall draws heat from the footings/ground all the way to the rafters in the winter and cooling in the summer.  What happens to this process when the wall is draining heat from the floor?  Does the in floor heat get drained all winter long?

I just do not see any way of preventing a thermal bridge without compromising the structure of the floor attaching to the wall.

Has anyone installed a suspended concrete floor in an ICF house without having a thermal bridge?

Any help here is greatly appreciated!
AltonUser is Offline
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25 Mar 2021 10:01 PM
If I understand your problem correctly, then I think the following approach will eliminate the thermal bridge, but do not use this until approved by a structural engineer. 1. Insulate under the footer with Expanded Polystyrene. Use the appropriate type that will support the load. 2. Build the basement wall with a 12" concrete core. 3. Place ICF floor on the ledge created by the thicker concrete core. 4. Build main floor with 7" concrete cores as planned.
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AltonUser is Offline
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27 Mar 2021 01:20 AM
The lifespan of a suspended floor slab depends upon maintaining the integrity of the reinforcing bar. I would rather not do that since the rebar may eventually rust and allow failure of the slab. One away around this without placing a thicker basement wall is to place the floor slab flush with the outside edge of the 7" concrete core in the basement wall. This still allows the slab to be tied to the wall with bent rebar, but I feel better knowing that the slab is bearing on top of the basement wall and not being suspended. I worry less about the rebar shearing off. This way allows the outer EPS of the ICF block to insulate the edge of the slab. Additional EPS can be glued on as a band to increase R-value. If interested, ask a structural engineer. Also, since the edge of the floor slab is supported by the basement wall, it might be a good idea to ask about using GatorBar instead of steel rebar.
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Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu Use email format with @ and period .
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GoGreenSeleneUser is Offline
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02 Apr 2021 10:36 PM
Posted By Alton on 25 Mar 2021 10:01 PM
If I understand your problem correctly, then I think the following approach will eliminate the thermal bridge, but do not use this until approved by a structural engineer. 1. Insulate under the footer with Expanded Polystyrene. Use the appropriate type that will support the load. 2. Build the basement wall with a 12" concrete core. 3. Place ICF floor on the ledge created by the thicker concrete core. 4. Build main floor with 7" concrete cores as planned.


Honest question here: Do you really think that insulating with Expanded Polystyrene will get the job done correctly?
GoGreenSeleneUser is Offline
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02 Apr 2021 10:37 PM
I haven’t done that. And while not exactly an expert on this matter, I do think that not having a thermal bridge can get things a little bit complicated.
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