Floating slab on grade detail at exterior door 1

[gte447f]

For a floating slab on grade, what is best practice at an exterior door? I assume the slab edge should get extended to the outside face of the wall. Does the slab edge need to be thickened? If so, how much, or should it be turned down onto the strip footing/grade beam? It seems to me that if the slab is isolated from the footing/exterior wall at the typical perimeter section, then it should remain isolated from the strip footing at an exterior door? Do others agree or disagree? This is in an area where frost heave is not a big concern (frost depth typically 12" by code, but probably actually less than that). The slab is 5" thick. The strip footing is 1'-4" thick x 2'-6" wide and is 1'-4" below slab.

See attached sketch of basic alternatives that I am thinking about.

 

[Ron]

All of your options will work. Pick the easy one to prevent contractor brain damage. My preference is option 3

 

[gte447f]

Ron, thanks for your input. I am leaning toward option 3 also... and a star for you for making me laugh. Leave it to engineers to over complicate things.

Buggar, I can see the benefit in leaving a block out for the threshold sometimes. How deep (vertically) do you block out for the threshold when you do this?

HotRod10, good points. I think door performance (i.e. actually opening and closing without getting stuck, etc.) trumps other considerations like slab cracking. If the slab is tied to the foundation, then as you say, there won't be any issues with door operation, so I am leaning toward that option. As far as possible movement, assuming the subgrade is prepared properly, I would assume it would be the foundation that would settle more than the slab, since the foundation will typically have higher, more sustained loading than the slab. However, if the foundation is placed against undisturbed, in-situ soil and the slab is placed against fill that is maybe not well compacted, then maybe the slab could settle more than the foundation. Either way, assuming differential settlements will not be excessive (less than 1/2"), maybe their is no harm in connecting the slab to the foundation at the door.

 

[BridgeSmith]

"Either way, assuming differential settlements will not be excessive (less than 1/2"), maybe their is no harm in connecting the slab to the foundation at the door."

As long as the slab has sufficient strength. In the case of slab settlement, it may have to accommodate spanning from the foundation wall to where it is supported by the slab fill. In the case of foundation settlement, it will need sufficient strength for the slab to support itself at the doorway if the foundation doesn't.

That's assuming the slab only rests on the foundation and is not tied down to it. If the slab has a positive connection to the foundation, either intentionally or incidentally, it could put significant stress on the slab if the foundations settles. Actually isolating the slab from the foundation can be more difficult to accomplish in the field than on paper. Vertical joints in particular must be constructed carefully to avoid snag points.

 

[bones206]

Has anyone ever considered using plate dowels to support the slab from the stem wall in a case where there is heavy traffic loads through the door? I generally use WARose's detail at doors (i.e. top of stem wall flush with slab w/ 1/2" isolation joint). I've never heard of them being used in a stem wall before, but it seems like it would be a good option in some cases.

 

[hetgen]

I normally do what @WARose said and let the architect deal with the door threshold detail. ( see detail below)