Concrete Basement Wall Extension

[GaStruct]

Hi All,

Long time reader, first time posting.

I have a client that wants to extend his 6" concrete basement wall 2'-0" to increase the ceiling height and re-grade his yard (the house has been demolished to the foundation).

How would you go about dealing with this hinge? The required embedment to lap and to develop a post installed #4 bar is about 30". Hilti only allows a 5" embedment for a 6" wall with HY-200 adhesive! My only thought would be to reduce the capacity by the ratio of 5/30 and see if that is greater than the applied forces (should be small this high up).

It just feels crazy to not try to get this to work as underpinning also creates a hinge even lower on the wall but that gets done semi-frequently. No way dowels are getting embedded the required length.

Let me know your thoughts. Rough sketch is attached.

 

[XR250]

I would figure out your actual demand on the rebar and see if it meets Hilt's published capacity.
There is more to it though, if he is regrading and adding fill, the demand on the middle portion of the wall will also increase. So that has to be checked.
Sounds like a risky job that I would turn away.

 

[SWComposites]

cripe, if its demo'd down to the foundation, why not just demo that also and build a proper foundation rather than trying to scab something onto the existing narrow wall. and they probably want to build a 2 - 3 story house? ugh.

 

[XR250]

That's what I was thinking. Pennywise and pound foolish.

 

[GaStruct]

@XR250 - Agreed on the increased loading of the wall. Was going to require X-ray of conc. for rebar spacing and check the IRC table for the smallest bar at that spacing. The sticking point for me is the post installed dowel probably won't work but I keep going back to every underpinning detail I have ever seen. Those dowels are not developed (sometimes not even present - just grout).

@SWComposites - They are replacing a one-story house with another one-story house (insane...i know). But, demolishing and rebuilding the fdn would be a big expense that is not required for the same loading.

Since I probably won't be able to get the numbers to work at the hinge, I got the client to agree to not re-grade his yard. They will just build a wood cripple wall to get the ceiling height and install full height steel tubes to take care of that hinge and have the conc. span horizontal.

 

[XR250]

You could also try building a 2x8 or 2x10 full-height stud wall inside to brace the concrete. I have done that before to repair bulging foundation walls. Was pretty effective.

 

[GaStruct]

I like that a lot. What's your connection of the studs to the conc? Or just bearing?

 

[XR250]

What ever the shear works out to be. Gotta do a freebody diagram.
Usually, 1/2"Ø epoxy anchor @ 12-16" O.C.and joist hangers between the studs and the bottom plate.
In your case, most of the load will be at the top though.

 

[GaStruct]

Gotcha but I was actually referring to the connection between the vertical studs and vertical conc. wall. Would technically work in bearing but I always like positive mechanical connections.

 

[XR250]

Ahh got it.
Bearing on the edge of the stud if the wall is straight. Otherwise, I usually show 2x6 stand-offs oriented horizontally and installed tight to the concrete and face nailed to the stud.

 

[lexpatrie]

Seems like you could make this work.

You may want them to excavate to add a drain tile at the base of the wall (if it's occupied space, IRC, etc), so then it gets less and less worthwhile. Exterior insulation on the foundation wall?