wood wall over cmu low wall condition?

[radiocontrolhead]

I'm working with an existing condition where they constructed a wood framed wall over a cmu low wall.

Not a fan of the condition but the project is a 2nd story addition over an existing car port. The (E) roof framing will be removed but they would like to maintain as much of the existing perimeter (3 sided) wall structure as possible. These walls are also along three property lines.

I am leaning toward a design that does not rely on the existing wall for any substantial gravity support (nothing more than the original loads imposed prior to the new work).

However I would like to sheath the wall with plywood for new shear resistance. provided furring strips are provided at the cmu portion of the wall is there any issue with this as all the force is in plane and not out of plane? I can't seem to shake off the idea that if i'm introducing new elements to an existing element it becomes mine. If you are also in agreement with my thoughts what could be done to support the wall? What comes to mind are "vertical girts" at said spacing which effectively decouples the cmu wall entirely and is used primarily as a property wall but serves no structural value.

Sorry for the long post, thank you for your time!

 

[Backcheckrage]

Some thoughts:
1. If you're going to rely on the old CMU "parapet" to act as a cantilever from the floor to prevent "hinging" there should be adequate anchorage of the floor to the parapet (adequate out of plane ties).

2. If you're not going to rely on the CMU wall act as a cantilever, still need good out of plane anchorage but horizontal spanning girders or strong backs needed and then vertical strongbacks to transfer that girder reaction to the roof and floor diaphragm.

3. Depending on the scale of the project keeping the existing timber walls is a good idea, especially if they're in good condtion.

4. Yes if you're putting a new roof structure on top, it's new loads and the original building should be able to take that gravity and lateral loads.

Hope this helps?