Grouting hollow CMU at change in thickness

I don't know of any requirements in TMS 402 (ACI 530) regarding this, but it is often good practice to have the thicker wall below be grouted at least at the top course. This gives more bearing area for the thinner wall since you would only have thin webs supporting the wall (potentially). If you have a thicker wall over a thinner wall (not likely), I would follow the corbelling requirements. And I think you have more issues with the vertical bar and where it is in each portion of the wall than with a solid course. That may be the biggest challenge.

Thanks. I usually see it grouted but not in this case! I think the math will work out regardless.

It'll come down to your effective net area calculation. The face shell hanging over the open cells will have virtually no contact area, thus spiking both your flexural and axial compressive and net tension flexural stresses there.

Beyond the strength concerns posted - without grouting at least the top course solid - you would have an empty cavity that could fill up with water, debris, bugs etc. Feels like a no-brainer to grout that section solid.

"Beyond the strength concerns posted - without grouting at least the top course solid - you would have an empty cavity that could fill up with water, debris, bugs etc.

There will be brick veneer in front of it so probably not a big issue.

"It'll come down to your effective net area calculation. The face shell hanging over the open cells will have virtually no contact area, thus spiking both your flexural and axial compressive and net tension flexural stresses there."

I haven't put numbers to it yet. I will have vertical rebar at 24" O.C. in grouted cells so that will take the bending and honestly, probably the axial as the wall will span between columns.

Thanks!

FYI, found this in the IRC....