Slab Ledge at Foundation Walls

[RFreund]

I'm curious to know others feelings on the attached detail where the foundation wall is notched for the slab. Is there any concern for cracking due to the soil settling more than the portion of the slab that is over the foundation wall? I would think that any difference would be small and not cause any issues. How about the thickened slab edge? Usually I'm not a fan due to the increased "drag" during shrinkage but maybe I'm wrong here.

I suppose this relates to this thread as well:

http://www.eng-tips.com/viewthread.cfm?qid=368578

EIT
www.HowToEngineer.com

 

[manstrom]

I assume that is an edge footing detail for a deep frost depth. I don't see a footing.

I prefer the slab to sit on the foundation wall as shown. Otherwise, the slab and footing will settle separately. I don't like the new trend of adding this insulation, but it is unavoidable. I usually leave out a chunk of insulation every 4' or so to give the slab positive contact with the wall.

If anything the slab will settle more than the footing since the slab subgrade isn't as well compacted and was probably disturbed during excavation of the footer.

The thickened slab edge gives them a little room for error. I don't see an issue.

 

[msquared48]

I do not like it for a couple of reasons:

1. The slab will need extra reinforcing to control cracking as the support at the wall is a hard point and differential deflection will occur, and

2. I do not know what the width of the stem wall for the footing is, but it does not seem to provide much width for either the installation of any sill plate anchor bolts or hold downs if there are any shear walls.

I would move the outside face of the insulation to the inside face of the wall and cover it with trim or a 1.5" skim coat of concrete. Damn the thermal aspects here. Structure controls.

Mike McCann, PE, SE (WA)

 

[KootK]

It makes me want to barf a little but I've used similar details in the past without issue. I've also done a ton of projects where the slab and wall were independent, facilitating a later SOG pour. No problems there either.

Interesting point about the drag on the downturn. I hadn't considered that before.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[RFreund]

Hmmm... These concrete joint and slab on grade details really seem to trip me up.
Interestingly enough the Dept. of Energy has no problem recommending this:

http://web.ornl.gov/sci/buildingsfoundations/handbook/section4-2.shtml

http://web.ornl.gov/sci/buildingsfoundations/handbook/section4-1.shtml

I really like to keep the slab isolated without bearing on the foundation wall. The slab does its thing the foundation does something a little different and no one knows the wiser.

In this case they are using some composite vinyl tile. I suppose if you have tile and a 5.5" metal stud wall with an 8" or 12" foundation wall thickness you probably want to have the ledge so that there is not a joint which may show up through the tile. Regardless of the insulation situation. Didn't we stop trying to reduce carbon output after we found out one vulcano eruption erases all our gains?

EIT

http://www.HowToEngineer.com

 

[slickdeals]

I recently did a detail similar to that one. Except that I did not have a turned down edge. It seemed to work okay so far.