ICF Block 3

[I-beam]

I have a client who is using a ICF foundation wall system for a house, with conventional wood framing above. The form is 13" wide, with a 8" core for concrete, so side walls of the form are 2.5" thick. This arrangement will have the 2x6 sill plate of the 2-level house only bearing on 3" of concrete, and hanging 2.5" out over the form side wall. Doesn't seem like a good detail to me. The manufacturer's details only show ICF walls. Anybody have any experience with this …./ suggestions

 

[dhengr]

I-beam:
Boy, it’s been a long time since I’ve thought about that detail, and I’ve only seen and dealt with it a few times. What I’ve seen done or had done, was on the top course or two of the ICF blks., you cut off that outer 2.5” shell, cut it away, and form that area out to be filled with conc., to full width on the outside, almost like a brick ledge. Put a little extra rebar up there to sorta form a bond beam. On a formed conc. wall or a conc. blk. wall, I’ve also used the argument that I can let the 2x6 sill pl. and the 2x6 studs hang over by 2” to match and cover 2” of rigid foam insul. on outside of the found. wall. The reasoning…, I show that the remaining stud wall (same as a 2x4 stud wall) will check in bearing, compression perpendicular to the grain on the sill pl., etc., so there is no problem with the 2” overhang on the 2x6 wall. The reason I like the straight formed brick ledge detail on the ICF wall is that the 8” conc. core in those walls can really be irregular, so the 2x6 sill pl. overhang is often far more than 2 or 2.5”.

 

[JAE]

The 2x6 should be on the 8" concrete - not on the 2 1/2" foam. The "wall" is the concrete wall. The foam is only a form material and is not structural and should not be treated as "really there".

 

[darthsoilsguy2]

the problem is that envelope design for the basement is a continuous insulation system but above it is wall cavity above. Insulate the walls with rigid, bring the wall back to the core and flash it good, or create a concrete ledge like dhengr.

 

[XR250]

Cantilever the floor framing out over the foam to support the loads.

 

[phamENG]

If it's truly a sill plate (between the foundation wall below and the floor joist above) and not a sole plate (bottom plate of a wall), why does it have to be 2x6? Use a 2x10 aligned with the outside face of the foam and you'll have plenty bearing on the concrete. You get a little "cantilever" in the joist, but a 2x10 cantilevering a couple inches isn't worth losing sleep over.

If it's the sole plate you're referring to - can you bring it in, align with the concrete, and then work with the architect to adjust the finish? Maybe some trim that steps in the couple inches, or moving some of the wall insulation outside to align with the ICF below (which could maintain a more consistent envelope for them).

 

[Brad805]

Several manufacturers (Nudura, FOX..) have a taper top that will reduce the 2.5" dimension to 1/2".

https://www.nudura.com/divisions/nudura-products/icf-series

We have also used 2"x12" top plates or engineered lumber that is ripped down to size.

 

[North2South]

I like XR250’s idea of cantilevering joists. Another option would be to put the 2x6 plate on the concrete with full bearing on the concrete and frame the wall as usual. Then come back and add an offset 2x4 to each wall stud to get the face of wall 2.5” out.

 

[XR250]

You get a little "cantilever" in the joist, but a 2x10 cantilevering a couple inches isn't worth losing sleep over.

I agree as long as the floor system cantilevers out with it (the 2x10 sole plate). If not, then, yes, I would lose sleep over it.

 

[phamENG]

XR250 - yes, by cantilever I'm referring to the joist as you mentioned (I see the confusing by using 2x10 twice - could be a 2x12, TJI, truss, whatever). I don't think of the sill as being a cantilever - that might imply bending induced tension perpendicular to the grain and yes, I would also loose sleep over that.

I would use the wider sill to make sure that I have sufficient bearing on the concrete AND to make sure I have a good load path for sheathing the sheathing. If you set the sill back from the face of the wall, you have to take any shear through the ends of the joists to the sill and anchors, rather than straight to the sill.