There is no code requirement that I know of. A thickness of 1.5" has been standard practice in my experience, but 1" is okay if you can place the grout uniformly under the entire base plate.

I feel the same way. 1" is on the tight side for large/long foundations.

Thanks

In my experience, the grouts used for that purpose are high-strength and non-shrink, so they have compressive strengths greater than the concrete mix in the foundation. Their purpose is to permit the accurate setting of the leveling plate so that the column base is level and in full contact with the foundation for it. 1" should be an adequate thickness for this purpose.

The greater concern is to have the base plate and the leveling plate sized to accommodate the total design column load in order for the load to be distributed to the foundation in a way that does not exceed the compressive and shear strength of the concrete.

Thanks for the insight and recommendation. We do plan to specify levelling plates. Our initial approach is to specify base plate and shims only.