6" Wide Concrete Stem Wall 1

[bigmig]

I have been doing this awhile and had a question come across my horizon that I was surprised I had not heard before.
Someone suggested doing a 3 ft tall crawl space cast in place concrete wall in a 6" width, as opposed to the 8" that is what I have always used.

My location is in the mountains, so winter weather is a reality. My architect said it doesn't matter if the wall is 6 or 8" in terms of insulation.

The wall will be braced by the floor (wood) system in the condition where the joists are perpendicular to the wall. In the parallele to wall condition,
there would be no bracing from the floor system.....so it would be a 36" tall by 6" wide wall 'arching' 32 feet between transverse walls. Granted the back fill will not be sloped
and we are not anticipating any type of surcharge load.

Has anyone used a 6" wide reinforced concrete wall for such an application? Is there a good reason not to? Do we all just use 8" because that is "what everyone does"?

 

[jayrod12]

Can't you provide blocking at the parallel to wall condition to brace it?

I haven't done this, but I guess theoretically it's possible. I would likely design around a single layer of rebar in the centre of wall.

 

[kipfoot]

I agree that you should use blocking where joists run parallel to the wall, as jayrod12 suggests.

Also, have a look at the IRC: TABLE R404.1.2(2) MINIMUM VERTICAL REINFORCEMENT FOR 6-INCH NOMINAL FLAT CONCRETE BASEMENT WALLS

 

[msquared48]

I agree too, and, in the mountains, there is a surcharge - ground snow and ice loading.

Mike McCann, PE, SE (WA)

 

[KootK]

I started of thread of my own on 6" walls a while back: Link. My concerns mostly center around constructability and quality of the finished product. And some other folks, especially bridge guys, seem to share that concern. On the other hand, I recently did some work in the pacific northwest using precisely the system that you've described. Apparently it's ubiquitous there and has a satisfactory record of performance.

32' strikes me as a long way to span horizontally. I expect that your behavior would be closer to that of a cantilevered retaining wall to the extent that any real retaining actually takes place. I definitely agree with Jayrod and others regarding the recommendation to install blocking adjacent to the stem wall to secure its top edge. With or without the blocking, I suspect that the tops of the stem walls will wind up pushing against the diaphragm. Might as well have something competent there.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.