Ray K wrote:
To clarify, I want to go no more than 1/2" in from the wallboard (the
base molding is 3/4" thick). So the gap to the sill plate would be the
thickness of the wallboard, plus the gap I cut. This is more than the
required 1/4" for the laminate, but the practical realities of the
presence of the wallboard must be considered.

If you have required clearance from the fixed sill plate I'd second the
previous suggestion of simply cutting the wallboard just above the floor
surface.

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