Hi Scott,
It’s a good question, with regional answers based on the grid, the speed at which is gets renewable and what is considered in your embodied scope.
In our Path To Zero Carbon Series, we show a (mostly) Mass Timber building in a very clean electric grid with an overwhelming majority of emissions from embodied, admittedly a bit of a unicorn. It’s the third graphic down.
https://lmnarchitects.com/lmn-research/03-toward-zero-carbon-architecture
We looked at the 13 projects reported for the 2021 AIA 2030 reporting cycle, and here is the number of years before Annual Energy Use Carbon is greater than Embodied Carbon. This includes structure, envelope, most interiors, plus a simplistic +60MTCO2e/m2 for MEP.
Infinite, infinite, 41, 29, 23, 14, 13, 11, 7, 7, 7, 6, 3.
If we use the Cambium 2040 Blended data for energy use carbon decreasing over time, we get:
Infinite, 70, 48, 39, 32, 28, 27, 25, 24, 23, 15, 12, 4.
So with a 30-year timeframe and Cambium energy data, a 50/50 average is not that far off, though with significant deviation.
-Kjell